Major interaction on record — check this product against your medications before combining. Based on 8 of 9 ingredients. Check your meds →
Dietary supplement

L-Theanine Ingredients & Drug Interactions

by Dr. Berg

L-Theanine label
See full label image
Capsule Category: Other Combinations
Most serious interaction: Major
Clinical methodology reviewed by · Updated Sep 16, 2026 · Label data from the NIH DSLD
What is this page for?

First and foremost: checking L-Theanine against your medications. The heart of this page is the interaction checker and the full interaction report — how this product’s ingredients may interact with prescription and over-the-counter medicines you may be taking.

Around that, we add a pharmacist’s high-level view of the product as a whole — what’s inside, the evidence for its stated use, how transparent the label is, and what safety data exists — so you can see the full picture in one place. It’s educational information from our licensed clinical databases and the clinical staff at HelloPharmacist — not medical advice — and we don’t sell or endorse products. Our editorial policy

The interaction bottom line Most serious interaction: Major

L-Theanine is a dietary supplement by Dr. Berg with 9 active ingredients. Its ingredients are commonly taken for mental focus and alertness, coping with stress, fatigue and sleep loss.Based on those ingredients, 1,536 medications have a known interaction with it, the most serious rated major. The ingredients most likely to interact are Ashwagandha, Powder, Licorice, Powder, L-Theanine. Use the checker below to test your specific medication, or read the full HelloPharmacist Interaction Report.

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Check Your Meds Against L-Theanine by Dr. Berg

Ask about any prescription or over-the-counter medication and we check it for interactions with L-Theanine by Dr. Berg — and tell you which ingredient is responsible.

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HelloPharmacist Scorecard of L-Theanine by Dr. Berg

Our pharmacy team’s full take, with four database checks built into the cards below — a summary of what is known, not a grade of the product itself.

From our pharmacy team — supplement deep dive

Generated from HelloPharmacist’s pharmacist-curated databases and editorial rules · Last generated Jul 11, 2026

What’s inside

Low disclosure
Ingredient Transparency · database check
Low

Most active ingredients don't disclose an individual amount — you can't tell how much of each you're getting.

Why this rating?
  • The label discloses an exact amount for 4 of its 9 active ingredients.
  • “Proprietary Blend” is a proprietary blend — the label gives one combined amount (385 mg) without saying how much of each component you get.

Dr. Berg's L-Theanine is a capsule containing nine active and inactive ingredients.

The product includes a proprietary blend whose individual components are listed separately: L-theanine (an amino acid from tea), L-tyrosine (another amino acid), ashwagandha powder (an herbal adaptogen), zinc, manganese, copper, licorice powder, nutritional yeast, and desiccated bovine adrenal substance. The inactive ingredients are gelatin, microcrystalline cellulose, and magnesium stearate.

Does it work?

Moderate evidence
Evidence for Intended Use · database check
By FDA rules, dietary supplements can’t claim to treat, cure, or prevent disease — so labels speak in careful marketing language. We discern each product’s intended use from its name, label claims, and label statements, then grade the clinical evidence for that use. How these ratings are computed
Moderate

Some clinical evidence supports this product's ingredients for its stated purpose, but it isn't conclusive.

Why this rating?
  • The label markets this product for: Adrenal support.
  • We looked for evidence on: Addison disease, Adrenal insufficiency, Anxiety, Athletic performance, Chronic fatigue syndrome (CFS), Cognitive function — and 3 related terms.
  • The strongest evidence on file: Ashwagandha is rated "Possibly Effective" for Anxiety (Natural Medicines).
  • Also on file: Ashwagandha is rated "Possibly Effective" for Generalized anxiety disorder (GAD), Stress.
  • Also on file: Tyrosine is rated "Possibly Effective" for Cognitive function.

L-theanine is rated possibly effective for cognitive function, though the evidence base is limited. L-tyrosine is rated effective for phenylketonuria (PKU) and possibly effective for cognitive function and memory, but rated possibly ineffective for athletic performance.

Ashwagandha is possibly effective for insomnia, anxiety, stress, and generalized anxiety disorder. Zinc is effective for zinc deficiency and likely effective for Wilson disease, and possibly effective for acne, age-related macular degeneration, and diabetes.

Manganese is effective for manganese deficiency. Copper is likely effective for copper deficiency.

Licorice is possibly effective for atopic dermatitis (eczema) and canker sores. For several of these ingredients, the evidence is insufficient to rate their effects on conditions like Alzheimer disease, dementia, and bipolar disorder.

The evidence, ingredient by ingredient Tyrosine Ashwagandha Brewer's Yeast Licorice Zinc Theanine Manganese Copper

How safe is it?

Well-documented data
Safety Information · database check
Well characterized

Adverse-effect, pregnancy, and general safety data are on file for most of these ingredients.

Why this rating?
  • We hold adverse-effect (side-effect) data for 8 of the 8 matched ingredients.
  • Pregnancy & breastfeeding safety ratings cover 8 of 8.
  • General safety write-ups exist for 8 of 8.
  • Remember: this measures how much safety information exists. Thin data is not the same as being safe.

Zinc is generally well tolerated below the tolerable upper limit of 40 mg daily for adults; at higher doses it can cause abdominal cramps, diarrhea, metallic taste, nausea, and vomiting, and long-term high doses raise concern for copper deficiency. L-tyrosine is generally well tolerated but not well studied long-term; common side effects include fatigue, headache, heartburn, and nausea.

L-theanine is generally well tolerated short-term but long-term safety is unclear; it may cause headaches, drowsiness, and increased dream activity. Ashwagandha is generally well tolerated short-term in healthy adults, though it can cause diarrhea, gastrointestinal upset, nausea, and vomiting at typical doses, and rare cases of liver damage have been reported.

Manganese at high doses carries risk of Parkinson-like neurological symptoms. Licorice is well tolerated in small food amounts but high doses or long-term use of products containing glycyrrhizin can cause serious problems.

Pregnancy and breastfeeding safety data are limited for most of these ingredients; L-theanine and ashwagandha should be avoided during pregnancy and breastfeeding due to insufficient safety information. Licorice should be avoided in pregnancy due to links to harmful effects.

Side effects, ingredient by ingredient Tyrosine Ashwagandha Brewer's Yeast Licorice Zinc Theanine Manganese Copper

Meds to double-check

Major interaction found
Known Interaction Concern · database check
Major identified

At least one ingredient has a documented Major-severity interaction. Check your medications for a personalized result.

Why this rating?
  • 8 of the 8 matched ingredients can interact with medications — Manganese, Brewer's Yeast, Licorice, Copper, Ashwagandha, among others.
  • The most serious interaction on file is rated Major.
  • Some involve high-stakes drug classes: anticoagulant / antiplatelet drugs; immunosuppressants / transplant drugs; diabetes medications; heart-rhythm medications; lithium; Parkinson's medications.
  • For scale: 1,537 individual medications appear in the full list. A big number alone doesn't make a product dangerous — what matters is whether YOUR medication is on it, so run yours through the interaction checker on this page.

Before taking this product, check your medications against these drug types, listed from most to least serious: quinolone and tetracycline antibiotics, benzodiazepines, blood pressure and thyroid medications, blood thinners (warfarin), heart medications (digoxin), antidiabetes drugs, and antipsychotics. Also check any antidepressants, sedatives, or immunosuppressants.

If you take levodopa, do not combine it with this product without talking to your pharmacist first.

Check your own medication Run your meds through the checker above

The bottom line

Scorecard at a glanceFormula with limited ingredient disclosure with some supporting evidence for its stated purpose. Major medication interactions have been identified, and safety information is well characterized.

This product may help with cognitive function, anxiety, or sleep if you don't take medications for blood pressure, heart rhythm, blood clotting, antibiotics, thyroid function, diabetes, or mood — and especially if you're not on benzodiazepines or CNS depressants. If you're pregnant, breastfeeding, or on any regular prescription medication, talk to your pharmacist or doctor before starting; the multiple ingredients here interact with a wide range of drugs.

Run your exact medications through the checker on this page.

Educational only — not medical advice; always confirm with your pharmacist. Our editorial policy · How we use AI

Assessment coverage: 8 of 9 active ingredients matched to our full ingredient reviews (monographs). Based on the product label dated Jul 24, 2025.

This Scorecard evaluates available label information, ingredient evidence, and known medication-safety considerations. It does not independently verify product identity, purity, potency, contamination, or manufacturing quality. How these ratings are computed

At a glance

General information

Key facts about L-Theanine, straight from the product label.

Brand Dr. Berg
Net contents 90 Capsule(s)
Market status On market
Date entered into DSLD Jul 24, 2025
DSLD ID 337162
Product type Other Combinations
Supplement form Capsule
Dietary claims / uses Nutrient, All Other, Structure/Function
Intended target group(s) Adult (18 - 50 Years)
From the label
Everything in this section is reproduced from the manufacturer’s own product label — it’s the label speaking, not HelloPharmacist. We show it so you can see exactly what the maker states; we don’t verify or endorse those statements.

Supplement Facts

The label details for L-Theanine by Dr. Berg, sourced from the NIH Dietary Supplement Label Database.

Supplement Facts

Daily Value (DV) Target Group(s):
Adults and children 4 or more years of age
Minimum serving Sizes:
1 Capsule(s)
Maximum serving Sizes:
1 Capsule(s)
Servings per container
90
IngredientAmount% DV
Proprietary Blend385 mg--
Zinc0.4 mg4%
L-Tyrosine0 NP--
L-Theanine200 mg--
Ashwagandha, Powder0 NP--
Nutritional Yeast0 NP--
Manganese3 mg130%
Copper0.03 mg3%
Bovine Adrenal Substance, Desiccated0 NP--
Licorice, Powder0 NP--

Other ingredients: Gelatin, Microcrystalline Cellulose, Magnesium Stearate

Tap any ingredient to jump to its full detail below.

Label statements
These statements are the manufacturer’s wording, reproduced from the product label — the label is saying it, not HelloPharmacist. We don’t verify or endorse them.
Suggested/Recommended/Usage/Directions

Suggested use: As a dietary supplement, take 1 capsule, with meals, 3 times per day.

Precautions

Caution: Do not exceed recommended dose. Do not use if safety seal is damaged or missing.

Pregnant or nursing mothers, children under the age of 18, and individuals with known medical conditions should consult a physician before using this or any dietary supplement.

Pregnant or nursing mothers, children under the age of 18, and individuals with known medical conditions should consult a physician before using this or any dietary supplement.

FDA Disclaimer Statement

These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.

Storage

Store in a cool, dry place, with a lid.

General Statements

To reorder: shop.drberg.com

Brand IP Statement(s)

Dr. Berg The Knowledge Doc

Formulation

Adrenal support

Formula

L-theanine + L-tyrosine + Ashwagandha + Desiccated adrenal

FDA Statement of Identity

Dietary Supplement

Is this label outdated? Report a formula or label change and our pharmacy team will review it.

See for yourself

L-Theanine by Dr. Berg label

The label scan from the NIH Dietary Supplement Label Database. Tap to enlarge.

L-Theanine label

Label images are published by the NIH Dietary Supplement Label Database for the version of this product on file. Always read your actual product label.

View the full label (PDF)
What’s inside

The Ingredients in L-Theanine by Dr. Berg

These are the 9 active ingredients this product is made of. Select any to open its full monograph.

Serving size1 Capsule(s) Dosage formCapsule Servings per container90 Amounts shown are per serving.

Most supplement products combine several ingredients, and a medication can interact with the product through any one of them. Each ingredient below shows whether it has known drug interactions.

Proprietary Blend

385 mg per serving

Zinc

Interacts with
67 drugs
0.4 mg per serving Form: Zinc Amino Acid Chelate

Zinc is an essential mineral that your body needs for immune function, wound healing, taste, and smell. Most people get enough from food, but suppleme...

Zinc monograph & interactions

L-Theanine

Interacts with
565 drugs
200 mg per serving

Theanine (usually L-theanine) is an amino acid found naturally in tea leaves that many people take to feel calmer and less stressed without strong dro...

L-Theanine monograph & interactions

Manganese

Interacts with
83 drugs
3 mg per serving Form: Manganese Lactate

Manganese is an essential trace mineral your body needs in small amounts for bone formation, metabolism, and antioxidant defense, and most people get...

Manganese monograph & interactions

Copper

Interacts with
31 drugs
0.03 mg per serving Form: Copper Amino Acid Chelate

Copper is an essential trace mineral your body needs in small amounts for making red blood cells, supporting nerves and bones, and helping enzymes wor...

Copper monograph & interactions

Other (inactive) ingredients: Gelatin, Microcrystalline Cellulose, Magnesium Stearate. These complete the product’s ingredient list but are not active constituents.

Interaction report

L-Theanine by Dr. Berg Drug Interactions

Want to check YOUR meds against L-Theanine?

Ask about interactions with your drugs in plain English — “Can I take it with lisinopril?” — and we find you the answer in seconds, ingredient by ingredient.

 Go to the checker
1,536Drugs
9 Major 1,431 Moderate 96 Minor

Ingredients driving the most interactions

Ashwagandha, Powder 1,372
Licorice, Powder 1,040
L-Theanine 565
Nutritional Yeast 136
Manganese 83

Individual Drug Interactions

The ingredients in L-Theanine interact with 1,536 drugs. Click any drug to see the details.

8 of the 9 ingredients in L-Theanine interact with drugs. Each result below shows which ingredient is responsible. Ashwagandha, Powder Licorice, Powder L-Theanine Nutritional Yeast Manganese Zinc Copper L-Tyrosine

Each ingredient & the kinds of drugs it affects

For each ingredient in L-Theanine with known interactions, here are the types of medications they can affect. Open any type for the detail — or search your exact drug in the checker above.

Ashwagandha, Powder10 drug types · 1,372 drugs

Antidiabetes Drugs

Theoretically, taking ashwagandha with antidiabetes drugs might increase the risk of hypoglycemia.
There is preliminary clinical evidence suggesting that ashwagandha might lower blood glucose levels. Theoretically, ashwagandha might have additive effects when used with antidiabetes drugs and increase the risk of hypoglycemia.

Likelihood Possible Evidence B
Antihypertensive Drugs

Theoretically, taking ashwagandha with antihypertensive drugs might increase the risk of hypotension.
Animal research suggests that ashwagandha might lower systolic and diastolic blood pressure. Theoretically, ashwagandha might have additive effects when used with antihypertensive drugs and increase the risk of hypotension.

Likelihood Possible Evidence D
Benzodiazepines

Theoretically, taking ashwagandha might increase the sedative effects of benzodiazepines.
There is preliminary evidence that ashwagandha might have an additive effect with diazepam (Valium) and clonazepam (Klonopin). This may also occur with other benzodiazepines.

Likelihood Possible Evidence D
Cns Depressants

Theoretically, taking ashwagandha might increase the sedative effects of CNS depressants.
Ashwagandha seems to have sedative effects. Theoretically, this may potentiate the effects of barbiturates, other sedatives, and anxiolytics.

Likelihood Possible Evidence D
Hepatotoxic Drugs

Theoretically, taking ashwagandha with hepatotoxic drugs might increase the risk of liver damage.
Ashwagandha has been linked to cases of acute hepatitis, liver failure, hepatic encephalopathy, autoimmune hepatitis, the need for liver transplantation, and death due to liver failure.

Likelihood Possible Evidence D
Immunosuppressants

Theoretically, taking ashwagandha might decrease the effects of immunosuppressants.
Ashwagandha has demonstrated immunostimulant effects in humans. Animal research has shown that ashwagandha can attenuate the immunosuppression caused by cyclophosphamide.

Likelihood Possible Evidence D
Thyroid Hormone

Ashwagandha might increase the effects and adverse effects of thyroid hormone.
Concomitant use of ashwagandha with thyroid hormones may cause additive therapeutic and adverse effects. Preliminary clinical research and animal studies suggest that ashwagandha boosts thyroid hormone synthesis and secretion. In one clinical study, ashwagandha increased triiodothyronine (T3) and thyroxine (T4) levels by 41.5% and 19.6%, respectively, and reduced serum TSH levels by 17.4% from baseline in adults with subclinical hypothyroidism.

Likelihood Probable Evidence B
Cytochrome P450 1A2 (Cyp1A2) Substrates

Theoretically, ashwagandha might decrease the levels and clinical effects of CYP1A2 substrates.
In vitro research shows that ashwagandha extract induces CYP1A2 enzymes.

Likelihood Possible Evidence D
Cytochrome P450 3A4 (Cyp3A4) Substrates

Theoretically, ashwagandha might decrease the levels and clinical effects of CYP3A4 substrates.
In vitro research shows that ashwagandha extract induces CYP3A4 enzymes.

Likelihood Possible Evidence D
Serotonergic Drugs

Some animal studies have reported that ashwagandha can enhance serotonergic transmission by altering certain serotonin (5-HT) receptors. However, there is no evidence to suggest that ashwagandha increases the risk of serotonin-related effects, and there have been no published case reports of serotonin syndrome when combined with other serotonergic drugs. Nevertheless, due to the lack of extensive studies on the matter and the fact that ashwagandha appears to affect serotonergic pathways, it would be prudent to exercise caution when combining it with drugs that affect serotonin. [References: - Effects of Withania somnifera (Ashwaga ndha) on Stress and the Stress-Related Neuropsychiatric Disorders Anxiety, Depression, and Insomnia. Curr Neuropharmacol. 2021 Sep 14; 19: 1468–1495. - A Prospective, Randomized Double-Blind, Placebo-Controlled Study of Safety and Efficacy of a High-Concentration Full-Spectrum Extract of Ashwagandha Root in Reducing Stress and Anxiety in Adults. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3573577/]

Likelihood Possible Evidence C
Ashwagandha, Powder full monograph & interactions

Licorice, Powder18 drug types · 1,040 drugs

Antihypertensive Drugs

Theoretically, licorice might reduce the effects of antihypertensive drugs.
In human research, licorice increases blood pressure in a dose-dependent manner.

Likelihood Possible Evidence B
Cisplatin (Platinol-Aq)

Theoretically, licorice might reduce the effects of cisplatin.
In animal research, licorice diminished the therapeutic efficacy of cisplatin.

Likelihood Possible Evidence D
Corticosteroids

Theoretically, concomitant use of licorice and corticosteroids might increase the side effects of corticosteroids.
Case reports suggest that concomitant use of licorice and oral corticosteroids, such as hydrocortisone, can potentiate the duration of activity and increase blood levels of corticosteroids. Additionally, in one case report, a patient with neurogenic orthostatic hypertension stabilized on fludrocortisone 0.1 mg twice daily developed pseudohyperaldosteronism after recent consumption of large amounts of black licorice.

Likelihood Possible Evidence D
Cytochrome P450 2B6 (Cyp2B6) Substrates

Theoretically, licorice might increase levels of drugs metabolized by CYP2B6.
In vitro research shows that licorice extract and glabridin, a licorice constituent, inhibit CYP2B6 isoenzymes. Licorice extract from the species G. uralensis seems to inhibit CYP2B6 isoenzymes to a greater degree than G. glabra extract in vitro. Theoretically, these species of licorice might increase levels of drugs metabolized by CYP2B6; however, these interactions have not yet been reported in humans.

Likelihood Possible Evidence D
Cytochrome P450 2C19 (Cyp2C19) Substrates

Theoretically, licorice might increase levels of drugs metabolized by CYP2C19.
In vitro, licorice extracts from the species G. glabra and G. uralensis inhibit CYP2C19 isoenzymes in vitro. Theoretically, these species of licorice might increase levels of drugs metabolized by CYP2C19; however, this interaction has not yet been reported in humans.

Likelihood Possible Evidence D
Cytochrome P450 2C8 (Cyp2C8) Substrates

Theoretically, licorice might increase levels of drugs metabolized by CYP2C8.
In vitro, licorice extract from the species G. glabra and G. uralensis inhibits CYP2C8 isoenzymes. Theoretically, these species of licorice might increase levels of drugs metabolized by CYP2C8; however, this interaction has not yet been reported in humans.

Likelihood Possible Evidence D
Cytochrome P450 2C9 (Cyp2C9) Substrates

Theoretically, licorice might increase or decrease levels of drugs metabolized by CYP2C9.
There is conflicting evidence about the effect of licorice on CYP2C9 enzyme activity. In vitro research shows that extracts from the licorice species G. glabra and G. uralensis moderately inhibit CYP2C9 isoenzymes. However, evidence from an animal model shows that licorice extract from the species G. uralensis can induce hepatic CYP2C9 activity. Until more is known, licorice should be used cautiously in people taking CYP2C9 substrates.

Likelihood Possible Evidence D
Cytochrome P450 3A4 (Cyp3A4) Substrates

Theoretically, licorice might increase or decrease levels of drugs metabolized by CYP3A4.
Pharmacokinetic research shows that the licorice constituent glycyrrhizin, taken in a dosage of 150 mg orally twice daily for 14 days, modestly decreases the area under the concentration-time curve of midazolam by about 20%. Midazolam is a substrate of CYP3A4, suggesting that glycyrrhizin modestly induces CYP3A4 activity. Animal research also shows that licorice extract from the species G. uralensis induces CYP3A4 activity. However, licorice extract from G. glabra species appear to inhibit CYP3A4-induced metabolism of testosterone in vitro. It is thought that the G. glabra inhibits CYP3A4 due to its constituent glabridin, which is a moderate CYP3A4 inhibitor in vitro and not present in other licorice species. Until more is known, licorice should be used cautiously in people taking CYP3A4 substrates.

Likelihood Possible Evidence B
Digoxin (Lanoxin)

Theoretically, concomitant use of licorice with digoxin might increase the risk of cardiac toxicity.
Overuse or misuse of licorice with cardiac glycoside therapy might increase the risk of cardiac toxicity due to potassium loss.

Likelihood Possible Evidence D
Diuretic Drugs

Theoretically, concomitant use of licorice with diuretic drugs might increase the risk of hypokalemia.
Overuse of licorice might compound diuretic-induced potassium loss. In one case report, a 72-year-old male with a past medical history of hypertension, type 2 diabetes, hyperlipidemia, arrhythmia, stroke, and hepatic dysfunction was hospitalized with severe hypokalemia and uncontrolled hypertension due to pseudohyperaldosteronism. This was thought to be provoked by concomitant daily consumption of a product containing 225 mg of glycyrrhizin, a constituent of licorice, and hydrochlorothiazide 12.5 mg for 1 month.

Likelihood Possible Evidence D
Estrogens

Theoretically, licorice might increase or decrease the effects of estrogen therapy.
Theoretically, licorice might interfere with estrogen therapy due to estrogenic and anti-estrogenic effects.

Likelihood Possible Evidence D
Loop Diuretics

Theoretically, loop diuretics might increase the mineralocorticoid effects of licorice.
Theoretically, loop diuretics might enhance the mineralocorticoid effects of licorice by inhibiting the enzyme that converts cortisol to cortisone; however, bumetanide (Bumex) does not appear to have this effect.

Likelihood Possible Evidence D
Midazolam (Versed)

Theoretically, licorice might decrease levels of midazolam.
In humans, the licorice constituent glycyrrhizin appears to moderately induce the metabolism of midazolam. This is likely due to induction of cytochrome P450 3A4 by licorice. Until more is known, licorice should be used cautiously in people taking midazolam.

Likelihood Possible Evidence B
P-Glycoprotein Substrates

Theoretically, licorice might decrease the absorption of P-glycoprotein substrates.
In vitro research shows that licorice can increase P-glycoprotein activity.

Likelihood Possible Evidence D
Paclitaxel (Abraxane, Onxol)

Theoretically, licorice might decrease plasma levels and clinical effects of paclitaxel.
Multiple doses of licorice taken concomitantly with paclitaxel might reduce the effectiveness of paclitaxel. Animal research shows that licorice 3 grams/kg given orally for 14 days before intravenous administration of paclitaxel decreases the exposure to paclitaxel and increases its clearance. Theoretically, this occurs because licorice induces cytochrome P450 3A4 enzymes, which metabolize paclitaxel. Notably, a single dose of licorice did not affect exposure or clearance of paclitaxel.

Likelihood Possible Evidence D
Warfarin (Coumadin)

Theoretically, licorice might decrease plasma levels and clinical effects of warfarin.
Licorice seems to increase metabolism and decrease levels of warfarin in animal models. This is likely due to induction of cytochrome P450 2C9 (CYP2C9) metabolism by licorice. Advise patients taking warfarin to avoid taking licorice.

Likelihood Possible Evidence D
Cytochrome P450 1A2 (Cyp1A2) Substrates

Theoretically, licorice might decrease the levels and clinical effects of CYP1A2 substrates.
In vitro research shows that licorice induces CYP1A2 enzymes.

Likelihood Possible Evidence D
Methotrexate (Trexall, Others)

Theoretically, licorice might increase levels of methotrexate.
Animal research suggests that intravenous administration of glycyrrhizin, a licorice constituent, and high-dose methotrexate may delay methotrexate excretion and increase systemic exposure, leading to transient elevations in liver enzymes and total bilirubin. This interaction has not yet been reported in humans.

Likelihood Unlikely Evidence D
Licorice, Powder full monograph & interactions

L-Theanine3 drug types · 565 drugs

Antihypertensive Drugs

Theanine might lower blood pressure, potentiating the effects of antihypertensive drugs.
Animal research shows that theanine can lower blood pressure in spontaneously hypertensive animals. Theoretically, concomitant use of theanine and antihypertensive drugs might potentiate the antihypertensive activity.

Likelihood Possible Evidence D
Cns Depressants

Theoretically, theanine might have additive sedative effects when used in conjunction with CNS depressants. However, it is unclear if this concern is clinically relevant.
Theoretically, theanine may compete with glutamate and/or increase plasma gamma-aminobutyric acid (GABA) levels, which could cause CNS depression. In one clinical study, some subjects taking oral theanine reported drowsiness.

Likelihood Unlikely Evidence D
Serotonergic Drugs

Clinical studies regarding the effects of L-theanine on serotonin levels are conflicting. Some studies suggest it can increase serotonin levels in the brain while others report that it may decrease them. Nevertheless, there have been no reports of l-theanine being a causative agent in serotonergic-related side effects or serotonin syndrome.

Likelihood Unlikely Evidence C
L-Theanine full monograph & interactions

Nutritional Yeast4 drug types · 136 drugs

Monoamine Oxidase Inhibitors (Maois)

Theoretically, taking brewer's yeast with MAOIs might increase the risk of hypertension.
Brewer's yeast contains tyramine. Taking brewer's yeast with MAOIs might increase the risk for hypertensive crisis.

Likelihood Likely Evidence D
Antidiabetes Drugs

Taking brewer's yeast with antidiabetes drugs might increase the risk of hypoglycemia.
Clinical research shows that taking chromium-containing brewer's yeast can decrease levels of blood glucose in diabetic patients being treated with antidiabetes drugs.

Likelihood Possible Evidence B
Lithium

Theoretically, taking brewer's yeast with lithium might cause additive effects and side effects.
Some brewer's yeast products contains lithium.

Likelihood Possible Evidence D
Antifungals

Theoretically, taking antifungals with some brewer's yeast products might decrease the effectiveness of brewer's yeast.
Some brewer's yeast products contain live yeast. Therefore, simultaneously taking antifungals might kill a significant number of the organisms.

Likelihood Possible Evidence D
Nutritional Yeast full monograph & interactions

Manganese3 drug types · 83 drugs

Antipsychotic Drugs

Theoretically, the risk for manganese toxicity might increase when taken with antipsychotic drugs.
Hallucinations and behavioral changes have been reported in a patient with liver disease who was taking haloperidol and manganese. Researchers speculate that taking manganese along with haloperidol, phenothiazine-derivatives, or other antipsychotic medications might increase the risk of manganese toxicity in some patients.

Likelihood Possible Evidence D
Quinolone Antibiotics

Theoretically, manganese might reduce the absorption of quinolone antibiotics.
Manganese is a multivalent cation. Interactions resulting in reduced quinolone absorption have been reported between quinolones and other multivalent cations, such as calcium and iron.

Likelihood Probable Evidence D
Tetracycline Antibiotics

Theoretically, manganese might reduce the absorption of tetracycline antibiotics.
Manganese is a multivalent cation. Interactions resulting in reduced tetracycline absorption have been reported between tetracyclines and other multivalent cations, such as calcium and iron.

Likelihood Probable Evidence D
Manganese full monograph & interactions

Zinc10 drug types · 67 drugs

Bictegravir/Emtricitabine/Tenofovir Alafenamide (Biktarvy)

Theoretically, zinc might decrease levels of bictegravir/emtricitabine/tenofovir alafenamide by reducing its absorption.
Advise patients that bictegravir/emtricitabine/tenofovir alafenamide should be taken at least 2 hours before or 6 hours after zinc containing products.

Likelihood Probable Evidence D
Cephalexin (Keflex)

Zinc might decrease cephalexin levels by chelating with cephalexin in the gut and preventing its absorption.
A pharmacokinetic study shows that zinc sulfate 250 mg taken concomitantly with cephalexin 500 mg decreases peak levels of cephalexin by 31% and reduces the exposure to cephalexin by 27%. Also, taking zinc sulfate 3 hours before cephalexin decreases peak levels of cephalexin by 11% and reduces the exposure to cephalexin by 18%. By decreasing cephalexin levels, zinc might increase the risk of treatment failure. This effect does not occur when zinc is taken 3 hours after the cephalexin dose. To avoid an interaction, advise patients take zinc sulfate 3 hours after taking cephalexin.

Likelihood Probable Evidence B
Cisplatin (Platinol-Aq)

Theoretically, zinc might interfere with the therapeutic effects of cisplatin.
Animal research suggests that zinc stimulates tumor cell production of the protein metallothionein, which binds and inactivates cisplatin. It is not known whether zinc supplements or high dietary zinc intake can cause clinically significant interference with cisplatin therapy. Cisplatin might also increase zinc excretion.

Likelihood Possible Evidence D
Integrase Inhibitors

Theoretically, taking zinc along with integrase inhibitors might decrease the levels and clinical effects of these drugs.
Zinc is a divalent cation. Pharmacokinetic studies have shown that other divalent cations such as calcium and iron can decrease blood levels of the integrase inhibitor dolutegravir through chelation.

Likelihood Possible Evidence D
Penicillamine (Cuprimine, Depen)

Zinc might reduce the levels and clinical effects of penicillamine.
By forming an insoluble complex with penicillamine, zinc interferes with penicillamine absorption and activity. Zinc supplements reduce the efficacy of low-dose penicillamine (0.5-1 gram/day), but do not seem to affect higher doses (1-2.75 gram/day), provided dosing times are separated. Advise patients to take zinc and penicillamine at least 2 hours apart.

Likelihood Probable Evidence B
Quinolone Antibiotics

Zinc can decrease the levels and clinical effects of quinolones antibiotics.
Quinolones form complexes with zinc in the gastrointestinal tract, reducing absorption of both the quinolone and zinc if taken at the same time. Advise patients to take these drugs at least 2 hours before, or 4-6 hours after, zinc supplements.

Likelihood Probable Evidence B
Ritonavir (Norvir)

Zinc modestly reduces levels of ritonavir.
Clinical research shows that zinc might reduce serum ritonavir levels by chelating with ritonavir in the gut and preventing its absorption. In patients with HIV, ritonavir is taken with atazanavir to prevent the metabolism and increase the effects of atazanavir. A pharmacokinetic study shows that, in patients being treated with atazanavir/ritonavir, co-administration of zinc sulfate (Solvazinc tablets) 125 mg as a single dose or as multiple daily doses for 2 weeks reduces plasma levels of ritonavir by about 16%. However, atazanavir levels still remains high enough to prevent HIV virus replication. Therefore, the decrease in ritonavir levels is not likely to be clinically significant.

Likelihood Probable Evidence B
Tetracycline Antibiotics

Zinc might reduce levels of tetracycline antibiotics.
Tetracyclines form complexes with zinc in the gastrointestinal tract, which can reduce absorption of both the tetracycline and zinc when taken at the same time. Taking zinc sulfate 200 mg with tetracycline reduces absorption of the antibiotic by 30% to 40%. Demeclocycline and minocycline cause a similar interaction. However, doxycycline does not seem to interact significantly with zinc. Advise patients to take tetracyclines at least 2 hours before, or 4-6 hours after, zinc supplements to avoid any interactions.

Likelihood Probable Evidence B
Amiloride (Midamor)

Amiloride can modestly reduce zinc excretion and increase zinc levels.
Clinical research shows that amiloride can reduce urinary zinc excretion, especially at doses of 10 mg per day or more. This zinc-sparing effect can help to counteract zinc losses caused by thiazide diuretics, but it is unlikely to cause zinc toxicity at usual amiloride doses. The other potassium-sparing diuretics, spironolactone (Aldactone) and triamterene (Dyrenium), do not seem to have a zinc-sparing effect.

Likelihood Probable Evidence B
Atazanavir (Reyataz)

Zinc modestly reduces levels of atazanavir, although this effect does not seem to be clinically significant.
Clinical research shows that zinc might decrease serum atazanavir levels by chelating with atazanavir in the gut and preventing its absorption. Although a single dose of zinc sulfate (Solvazinc tablets) 125 mg orally does not affect atazanavir concentrations in patients being treated with atazanavir/ritonavir, co-administration of zinc sulfate 125 mg daily for 2 weeks reduces plasma levels of atazanavir by about 22% in these patients. However, despite this decrease, atazanavir levels still remain at high enough concentrations for the prevention of HIV virus replication.

Likelihood Probable Evidence B
Zinc full monograph & interactions

Copper2 drug types · 31 drugs

Penicillamine (Cuprimine, Depen)

Theoretically, taking copper with penicillamine might decrease the absorption of penicillamine; separate dosing by at least 2 hours.
Copper chelates penicillamine, which decreases its absorption and may reduce its clinical effects.

Likelihood Probable Evidence D
Contraceptive Drugs

Theoretically, taking copper with contraceptive drugs might increase the levels and toxic effects of copper.
A meta-analysis of clinical studies suggests that chronic use of oral contraceptives increases serum copper levels by a mean of 57 mcg/dL. In most people, this resulted in levels above the normal reference range for copper.

Likelihood Possible Evidence D
Copper full monograph & interactions

L-Tyrosine2 drug types · 21 drugs

Levodopa

Theoretically, tyrosine might decrease the effectiveness of levodopa.
Tyrosine and levodopa compete for absorption in the proximal duodenum by the large neutral amino acid (LNAA) transport system. Advise patients to separate doses of tyrosine and levodopa by at least 2 hours.

Likelihood Probable Evidence D
Thyroid Hormone

Theoretically, tyrosine might have additive effects with thyroid hormone medications.
Tyrosine is a precursor to thyroxine and might increase levels of thyroid hormones.

Likelihood Probable Evidence D
L-Tyrosine full monograph & interactions
The maker

Brand information

Manufacturer and brand details for L-Theanine, from the product label.

Dr. Berg

Name
Dr. Berg Nutritionals
Street Address
4501 Ford Avenue
City
Alexandria
State
VA
ZipCode
22302
Phone Number
800-816-8184
Web Address
shop.drberg.com
Pharmacist Counseling Corner

L-Theanine by Dr. Berg: Common Questions

Does L-Theanine by Dr. Berg interact with any medications?
Yes. Based on its ingredients, L-Theanine has a known interaction with 1,536 medications, including 9 rated major. Use the checker to see how it interacts with a specific drug.
How can one product interact with so many drugs?
L-Theanine contains 9 active ingredients, and an interaction can come from any of them. We check every ingredient, combine the results into one list per medication, and show which ingredient and mechanism is responsible.
Where does this information come from?
The product label data comes from the NIH Dietary Supplement Label Database (DSLD); the interaction data is built on the Natural Medicines database and reviewed by HelloPharmacist pharmacists.
Is this safe to take if I'm pregnant or breastfeeding?
L-theanine and ashwagandha should be avoided during pregnancy and breastfeeding — the safety data isn't there. Licorice should also be avoided in pregnancy. For the other ingredients, we don't have enough pregnancy and breastfeeding safety information on file. Talk to your pharmacist or OB provider before starting.
What does L-theanine do?
L-theanine is an amino acid from tea that's possibly effective for cognitive function — it may help with mental clarity and focus. It's generally well tolerated, though it can cause headaches or drowsiness in some people.
Why is zinc in this product if it blocks antibiotics?
Zinc is included because it's effective for zinc deficiency and likely effective for Wilson disease. The key is timing: if you're on quinolone, tetracycline, or other antibiotics affected by zinc, take them at least 2 hours before or 4–6 hours after this product, and your pharmacist can help you plan that.
Can I take this with my blood pressure or anxiety medication?
Both L-theanine and ashwagandha may lower blood pressure and have sedative effects, so combining them with blood pressure meds or anti-anxiety drugs could cause your levels to drop too far. Check your specific medications with the tool on this page and talk to your pharmacist — don't stop your medication, but your dose may need adjusting.
What are the most common side effects?
Zinc can cause abdominal cramps, diarrhea, nausea, metallic taste, or vomiting — usually dose-related. L-tyrosine may cause fatigue, headache, heartburn, or nausea. L-theanine may cause headaches or drowsiness. Ashwagandha can cause diarrhea, nausea, or vomiting at typical doses, though these are not common.

Written and reviewed by the HelloPharmacist editorial staff. Our editorial policy

Not sure if L-Theanine is safe with your meds?

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Label information is sourced from the NIH Dietary Supplement Label Database and reflects the product version on file; always read your actual product label. This page is for education only and is not a substitute for professional medical advice. Confirm with your pharmacist or doctor before combining supplements and medications.

L-Theanine label
Go deeper

The Full Monographs Behind L-Theanine’s Ingredients

Every ingredient we hold a full HelloPharmacist monograph for — uses, evidence, safety, and the complete interaction list.

Herb & supplement monograph

Tyrosine

Interacts with 21 drugs

L-tyrosine is an amino acid your body uses to make brain chemicals like dopamine and norepinephrine. Some studies suggest it may help mental performance during short-term stress, sleep loss,...

Read the full Tyrosine monograph → Herb & supplement monograph

Ashwagandha

Interacts with 1,372 drugs

Ashwagandha is an Ayurvedic herb most often taken to help with stress, anxiety, and sleep, and some small studies suggest it may help, though the evidence is still limited. It is generally w...

Read the full Ashwagandha monograph → Herb & supplement monograph

Brewer's Yeast

Interacts with 136 drugs

Brewer's yeast is a nutrient-rich fungus that provides B vitamins, protein, and minerals, and a related yeast product (S. boulardii) is used for some types of diarrhea. Most other health cla...

Read the full Brewer's Yeast monograph → Herb & supplement monograph

Licorice

Interacts with 1,040 drugs

Licorice root is a traditional remedy used for sore throats, coughs, and digestive complaints, but solid human evidence is limited for most uses. Regular licorice contains glycyrrhizin, whic...

Read the full Licorice monograph → Herb & supplement monograph

Zinc

Interacts with 67 drugs

Zinc is an essential mineral that your body needs for immune function, wound healing, taste, and smell. Most people get enough from food, but supplements can help correct or prevent a defici...

Read the full Zinc monograph → Herb & supplement monograph

Theanine

Interacts with 565 drugs

Theanine (usually L-theanine) is an amino acid found naturally in tea leaves that many people take to feel calmer and less stressed without strong drowsiness. Early research suggests it may...

Read the full Theanine monograph → Herb & supplement monograph

Manganese

Interacts with 83 drugs

Manganese is an essential trace mineral your body needs in small amounts for bone formation, metabolism, and antioxidant defense, and most people get enough from a normal diet. Supplements m...

Read the full Manganese monograph → Herb & supplement monograph

Copper

Interacts with 31 drugs

Copper is an essential trace mineral your body needs in small amounts for making red blood cells, supporting nerves and bones, and helping enzymes work. Most people get enough copper from fo...

Read the full Copper monograph →
Sources

Sources & How We Checked

L-Theanine's label data comes from the NIH Dietary Supplement Label Database; the ingredient interaction data is from the Natural Medicines database, reviewed by our pharmacists.

Content is written and reviewed by licensed HelloPharmacist pharmacists. See our data sources and editorial standards for how this information is built and checked.

The 260 references behind this product’s interaction data

Every citation that drives the interaction findings for this product’s ingredients, from the evidence-graded Natural Medicines (TRC Healthcare) database. Open an ingredient to browse its citations — links open the study on PubMed or the publisher’s site.

Zinc 88 references
  1. Barceloux DG. Zinc. J Toxicol Clin Toxicol 1999;37:279-92.
  2. Eby GA, Davis DR, Halcomb WW. Reduction in duration of common colds by zinc gluconate lozenges in a double-blind study. Antimicrob Agents Chemother 1984;25:20-4. DOI
  3. Smith DS, Helzner EC, Nuttall CE Jr, et al. Failure of zinc gluconate in treatment of acute upper respiratory tract infections. Antimicrob Agents Chemother 1989;33:646-8. PubMed
  4. Blondeau JM. Expanded activity and utility of the new fluoroquinolones: a review. Clin Ther 1999;21:3-40. PubMed
  5. Reyes AJ, Olhaberry JV, Leary WP, et al. Urinary zinc excretion, diuretics, zinc deficiency and some side-effects of diuretics. S Afr Med J 1983;64:936-41.
  6. Kugelmas M. Preliminary observation: oral zinc sulfate replacement is effective in treating muscle cramps in cirrhotic patients. J Am Coll Nutr 2000;19:13-5. PubMed
  7. Hebel SK, ed. Drug Facts and Comparisons. 52nd ed. St. Louis: Facts and Comparisons, 1998.
  8. Chan S, Gerson B, Subramaniam S. The role of copper, molybdenum, selenium, and zinc in nutrition and health. Clin Lab Med 1998;18:673-85. DOI
  9. Brewer GJ, Yuzbasiyan-Gurkan V, Johnson V, et al. Treatment of Wilson's disease with zinc: XI. Interaction with other anticopper agents. J Am Coll Nutr 1993;12:26-30. PubMed
  10. Fosmire GJ. Zinc toxicity. Am J Clin Nutr 1990;51:225-7.
  11. Lomaestro BM, Bailie GR. Absorption interactions with fluoroquinolones. 1995 update. Drug Saf 1995;12:314-33. PubMed
  12. Hansten PD, Horn JR. Drug Interactions Analysis and Management. Vancouver, WA: Applied Therapeutics Inc., 1997 and updates.
  13. Seelig MS. Auto-immune complications of D-penicillamine - A possible result of zinc and magnesium depletion and of pyridoxine inactivation. J Am Coll Nutr 1982;1:207-14. PubMed
  14. Neuvonen PJ. Interactions with the absorption of tetracyclines. Drugs 1976;11:45-54.. PubMed
  15. Hirt M, Nobel S, Barron E. Zinc nasal gel for the treatment of common cold symptoms: A double-blind, placebo-controlled trial. Ear Nose Throat J 2000;79:778-82.. DOI
  16. Simkin PA. Oral zinc sulphate in rheumatoid arthritis. Lancet 1976;2:539-42. PubMed
  17. Wray D. A double-blind trial of systemic zinc sulfate in recurrent aphthous stomatitis. Oral Surg Oral Med Oral Pathol 1982;53:469-72. PubMed
  18. Douglas RM, Miles HB, Moore BW, et al. Failure of effervescent zinc acetate lozenges to alter the course of upper respiratory tract infections in Australian adults. Antimicrob Agents Chemother 1987;31:1263-5. PubMed
  19. Lagiou P, Wuu J, Trichopoulou A, et al. Diet and benign prostatic hyperplasia: a study in Greece. Urology 1999;54:284-90. PubMed
  20. Ewing CI, Gibbs AC, Ashcroft C, David TJ. Failure of oral zinc supplementation in atopic eczema. Eur J Clin Nutr 1991;45:507-10.
  21. Food and Nutrition Board, Institute of Medicine. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington, DC: National Academy Press, 2002.
  22. Age-Related Eye Disease Study Research Group. A randomized, placebo-controlled, clinical trial of high-dose supplementation with vitamins C and E, beta carotene, and zinc for age-related macular degeneration and vision loss. AREDS report no. 8. Arch Oph
  23. Greenberg JE, Lynn M, Kirsner RS, et al. Mucocutaneous pigmented macule as a result of zinc deposition. J Cutan Pathol 2002;29:613-5. PubMed
  24. Godfrey HR, Godfrey NJ, Godfrey JC, Riley D. A randomized clinical trial on the treatment of oral herpes with topical zinc oxide/glycine. Altern Ther Health Med 2001;7:49-56.
  25. Turner RB. Ineffectiveness of intranasal zinc gluconate for prevention of experimental rhinovirus colds. Clin Infect Dis 2001;33:1865-70. PubMed
  26. Belongia EA, Berg R, Liu K. A randomized trial of zinc nasal spray for the treatment of upper respiratory illness in adults. Am J Med 2001;111:103-8. PubMed
  27. Mossad SB. Effect of zincum gluconicum nasal gel on the duration and symptom severity of the common cold in otherwise healthy adults. QJM 2003;96:35-43. DOI
  28. Leitzmann MF, Stampfer MJ, Wu K, et al. Zinc supplement use and risk of prostate cancer. J Natl Cancer Inst 2003;95:1004-7.. PubMed
  29. Jafek BW, Linschoten M, Murrow BW. Zicam Induced Anosmia. American Rhinologic Society 49th Annual Fall Scientific Meeting abstract. Orlando, Florida. September 20, 2003. http://app.american-rhinologic.org/programs/2003ARSFallProgram071503.pdf (Accessed 24
  30. Uebayashi H, Hatanaka T, Kanemura F, Tonosaki K. Acute anosmia in the mouse: behavioral discrimination among the four basic taste substances. Physiol Behav 2001;72:291-6.. PubMed
  31. Barrett S. Zicam Marketers Sued. United States District Court Western District of Michigan Southern Division, Filed October 14, 2003, Case No. 4:03CV0146.
  32. Bilici M, Yildirim F, Kandil S, et al. Double-blind, placebo-controlled study of zinc sulfate in the treatment of attention deficit hyperactivity disorder. Prog Neuropsychopharmacol Biol Psychiatry 2004;28:181-90.. PubMed
  33. Polk RE, Healy DP, Sahai J, et al. Effect of ferrous sulfate and multivitamins with zinc on absorption of ciprofloxacin in normal volunteers. Antimicrob Agents Chemother 1989;33:1841-4. PubMed
  34. Mery C, Delrieu F, Ghozlan R, et al. Controlled trial of D-penicillamine in rheumatoid arthritis. Dose effect and the role of zinc. Scand J Rheumatol 1976;5:241-7. PubMed
  35. Penttila O, Hurme H, Neuvonen PJ. Effect of zinc sulfate on the absorption of tetracycline and doxycycline in man. Eur J Clin Pharmacol 1975;9:131-4.
  36. Kondo Y, Yamagata K, Satoh M, et al. Optimal administration schedule of cisplatin for bladder tumor with minimal induction of metallothionein. J Urol 2003;170:2467-70. PubMed
  37. Doz F, Berens ME, Deschepper CF, et al. Experimental basis for increasing the therapeutic index of cis-diamminedicarboxylatocyclobutaneplatinum(II) in brain tumor therapy by a high-zinc diet. Cancer Chemother Pharmacol 1992;29:219-26.
  38. Wester PO. Urinary zinc excretion during treatment with different diuretics. Acta Med Scand 1980;208:209-12. PubMed
  39. Golik A, Modai D, Weissgarten J, et al. Hydrochlorothiazide-amiloride causes excessive urinary zinc excretion. Clin Pharmacol Ther 1987;42:42-4. PubMed
  40. Leary WP, Reyes AJ, Van der Byl K. Urinary magnesium and zinc excretion after two different single doses of amiloride in healthy adults. Curr Ther Res 1983;34:205-16.
  41. McBride K, Slotnick B, Margolis FL. Does intranasal application of zinc sulfate produce anosmia in the mouse? An olfactometric and anatomical study. Chem Senses 2003;28:659-70. PubMed
  42. Burd GD. Morphological study of the effects of intranasal zinc sulfate irrigation on the mouse olfactory epithelium and olfactory bulb. Microsc Res Tech 1993;24:195-213. PubMed
  43. Ducray A, Bondier JR, Michel G, et al. Recovery following peripheral destruction of olfactory neurons in young and adult mice. Eur J Neurosci 2002;15:1907-17. PubMed
  44. Mayer AD, Rosenblatt JS. Peripheral olfactory deafferentation of the primary olfactory system in rats using ZnSO4 nasal spray with special reference to maternal behavior. Physiol Behav 1993;53:587-92. PubMed
  45. DeCook CA, Hirsch AR. Anosmia due to inhalational zinc: a case report (abstract). Chem Senses 2000;25:659.
  46. Tisdall FF, Brown A, Defries RD. Persistent anosmia following zinc sulfate nasal spraying. JPed 1938;18:60-2. DOI
  47. Lawson KA, Wright ME, Subar A, et al. Multivitamin use and risk of prostate cancer in the National Institutes of Health-AARP Diet and Health Study. J Natl Cancer Inst 2007;99:754-64. PubMed
  48. Public Health Advisory. Loss of sense of smell with intranasal cold remedies containing zinc. U.S. Food and Drug Administration, June 16, 2009. Available at: http://www.fda.gov/Drugs/DrugSafety/PublicHealthAdvisories/ucm166059.htm (Accessed 16 June 2009)
  49. Dooren JC. FDA warns against use of Zicam. The Wall Street Journal, June 16, 2009. Available at: http://online.wsj.com/article/SB124516778692319231.html#mod=djemHL?mg=com-wsj (Accessed 16 June 2009).
  50. Alexander TH, Davidson TM. Intranasal zinc and anosmia: the zinc-induced anosmia syndrome. Laryngoscope 2006;116:217-20.
  51. Health Canada / GlaxoSmithKline Consumer Healthcare. Association of long-term, excessive use of zinc-containing Poli-Grip products with myeloneuropathy and blood dyscrasias. February 18, 2010. Available at: http://hc-sc.gc.ca/dhp-mps/alt_formats/pdf/medef
  52. GlaxoSmithKline Consumer Advisory. GlaxoSmithKline (GSK) warns about a potential health risk associated with long-term, excessive use of GSK's zinc-containing denture adhesives Super Polygrip Original, Ultra Fresh and Extra Care. February 18, 2010. Availa
  53. Science M, Johnstone J, Roth DE, et al. Zinc for the treatment of the common cold: a systematic review and meta-analysis of randomized controlled trials. CMAJ 2012;184:E551-61. PubMed
  54. Castilla-Higuero, L., Romero-Gomez, M., Suarez, E., and Castro, M. Acute hepatitis after starting zinc therapy in a patient with presymptomatic Wilson's disease. Hepatology 2000;32(4 Pt 1):877. PubMed
  55. Sharquie, K. E., Najim, R. A., Farjou, I. B., and Al Timimi, D. J. Oral zinc sulphate in the treatment of acute cutaneous leishmaniasis. Clin.Exp.Dermatol. 2001;26(1):21-26. PubMed
  56. Dreno, B., Moyse, D., Alirezai, M., Amblard, P., Auffret, N., Beylot, C., Bodokh, I., Chivot, M., Daniel, F., Humbert, P., Meynadier, J., and Poli, F. Multicenter randomized comparative double-blind controlled clinical trial of the safety and efficacy of
  57. Moore, R. Bleeding gastric erosion after oral zinc sulphate. Br.Med J 3-25-1978;1(6115):754. PubMed
  58. Jafek, B. W., Linschoten, M. R., and Murrow, B. W. Anosmia after intranasal zinc gluconate use. Am J Rhinol. 2004;18(3):137-141. DOI
  59. Simonart, T. and de, Maertelaer, V. Systemic treatments for cutaneous warts: a systematic review. J Dermatolog.Treat. 2012;23(1):72-77. PubMed
  60. Cochran, R. J., Tucker, S. B., and Flannigan, S. A. Topical zinc therapy for acne vulgaris. Int.J Dermatol. 1985;24(3):188-190. DOI
  61. Morgan, A. A. Bleeding gastric erosion after oral zinc sulphate. Br.Med.J. 5-13-1978;1(6122):1283-1284. PubMed
  62. Murphy, J. V. Intoxication following ingestion of elemental zinc. JAMA 6-22-1970;212(12):2119-2120.
  63. Lang, C. J., Rabas-Kolominsky, P., Engelhardt, A., Kobras, G., and Konig, H. J. Fatal deterioration of Wilson's disease after institution of oral zinc therapy. Arch Neurol. 1993;50(10):1007-1008. PubMed
  64. Fjellner, B. Drug-induced lupus erythematosus aggravated by oral zinc therapy. Acta Derm.Venereol. 1979;59(4):368-370. DOI
  65. Varas Lorenzo, M. J. Zinc acexamate and ranitidine in the short- and mid-term management of gastroduodenal ulcers. Curr Ther Res 21986;39:19-29.
  66. Bosch, F. and Jimenez, E. Post-marketing surveillance of zinc acexamate in peptic ulcer treatment. Clin Trials J 1990;27:301-312.
  67. DeCook, C. A. and Hirsch, A. R. Anosmia due to inhalational zinc: a case report (abstract). Chem Senses 2000;25:659.
  68. Crown LA, May JA. Zinc toxicity: denture adhesives, bone marrow failure and polyneuropathy. Tenn Med. 2012 Feb;105(2):39-40, 42.
  69. Dadamio J, Van Tournout M, Teughels W, Dekeyser C, Coucke W, Quirynen M. Efficacy of different mouthrinse formulations in reducing oral malodour: a randomized clinical trial. J Clin Periodontol. 2013 May;40(5):505-13. PubMed
  70. Moyle G, Else L, Jackson A, Back D, Yapa MH, Seymour N, Ringner-Nackter L, Karolia Z, Gazzard B, Boffito M. Coadministration of atazanavir-ritonavir and zinc sulfate: impact on hyperbilirubinemia and pharmacokinetics. Antimicrob Agents Chemother. 2013 Aug PubMed
  71. Zittel S, Ufer F, Gerloff C, Münchau A, Rosenkranz M. Severe myelopathy after denture cream use--is copper deficiency or excess zinc the cause? Clin Neurol Neurosurg. 2014 Jun;121:17-8. PubMed
  72. Jalloh MA, Gregory PJ, Hein D, et al. Dietary supplement interactions with antiretrovirals: a systematic review. Int J STD AIDS. 2017 Jan;28(1):4-15. PubMed
  73. Guidelines for the Use of Antiretroviral Agents in HIV-1-Infected Adults and Adolescents: Drug Interactions between Integrase Inhibitors and Other Drugs. AIDSinfo. July 14, 2016. Available at: https://aidsinfo.nih.gov/guidelines/html/1/adult-and-adolescen
  74. Ding Y, Jia YY, Li F, et al. The effect of staggered administration of zinc sulfate on the pharmacokinetics of oral cephalexin. Br J Clin Pharmacol. 2012 Mar;73(3):422-7. PubMed
  75. Fallah R, Sabbaghzadegan S, Karbasi SA, Binesh F. Efficacy of zinc sulfate supplement on febrile seizure recurrence prevention in children with normal serum zinc level: A randomised clinical trial. Nutrition. 2015;31(11-12):1358-61. PubMed
  76. Lazzerini M, Wanzira H. Oral zinc for treating diarrhoea in children. Cochrane Database Syst Rev. 2016;12:CD005436. PubMed
  77. Mahmoud AM, Al-Alem U, Dabbous F, et al. Zinc intake and risk of prostate cancer: Case-control study and meta-analysis. PLoS One. 2016;11(11):e0165956. PubMed
  78. Nagraj SK, George RP, Shetty N, Levenson D, Ferraiolo DM, Shrestha A. Interventions for managing taste disturbances. Cochrane Database Syst Rev. 2017 Dec 20;12(12):CD010470. PubMed
  79. Yee BE, Richards P, Sui JY, Marsch AF. Serum zinc levels and efficacy of zinc treatment in acne vulgaris: A systematic review and meta-analysis. Dermatol Ther. 2020:e14252. PubMed
  80. Janyajirawong R, Vilaichone RK, Sethasine S. Efficacy of zinc supplement in minimal hepatic encephalopathy: A prospective, randomized controlled study (Zinc-MHE Trial). Asian Pac J Cancer Prev 2021;22(9):2879-2887. PubMed
  81. Nakano M, Nakamura Y, Miyazaki A, Takahashi J. Zinc pharmacotherapy for elderly osteoporotic patients with zinc deficiency in a clinical setting. Nutrients 2021;13(6):1814. PubMed
  82. Tolino E, Skroza N, Mambrin A, et al. An open-label study comparing oral zinc to lymecycline in the treatment of acne vulgaris. J Clin Aesthet Dermatol 2021;14(5):56-58.
  83. Hunter J, Arentz S, Goldenberg J, et al. Zinc for the prevention or treatment of acute viral respiratory tract infections in adults: a rapid systematic review and meta-analysis of randomised controlled trials. BMJ Open. 2021;11(11):e047474. PubMed
  84. Yamazaki K, Kageyama H, Fujiyama T, Ito T, Urano S, Honda T. A case of systemic contact dermatitis due to zinc supplements. Int J Dermatol 2022. PubMed
  85. Magham K, Han J, Eilbert W, Bunney EB. Severe copper deficiency anemia caused by zinc supplement use. Am J Emerg Med 2023;72:222. PubMed
  86. Sivakumar RR, Chinnaiah Govindareddy D, Sahoo J, Bobby Z, Chinnakali P. Effect of daily zinc supplementation for 12 weeks on serum thyroid auto-antibody levels in children and adolescents with autoimmune thyroiditis - a randomized controlled trial. J Pedi PubMed
  87. AlDhasee O, AlMalki H, AlKharashi N, AlJeraisy N, Al Deeb M. Acute zinc sulfate overdose: clinical presentation and management. BMJ Case Rep 2025;18(1):e263899. PubMed
  88. US Food and Drug Administration (FDA). Biktarvy Prescribing Information. October 2024. Available at: https://www.accessdata.fda.gov/drugsatfda_docs/label/2024/210251Orig1s020lbl.pdf. Accessed July 16, 2025.

See these in context on the Zinc monograph →

Tyrosine 4 references
  1. Meyer JS, Welch KM, Deshmukh VD, et al. Neurotransmitter precursor amino acids in the treatment of multi-infarct dementia and Alzheimer's disease. J Amer Geriat Soc 1977;25:289-98.
  2. DiPiro JT, Talbert RL, Yee GC, et al; eds. Pharmacotherapy: A pathophysiologic approach. 4th ed. Stamford, CT: Appleton & Lange, 1999.
  3. Wood DR, Reimherr FW, Wender PH. Amino acid precursors for the treatment of attention deficit disorder, residual type. Psychopharmacol Bull 1985;21:146-9.
  4. van Spronsen FJ, van Rijn M, Bekhof J. Phenylketonuria: tyrosine supplementation in phenylalanine-restricted diets. Am J Clin Nutr 2001;73:153-7. PubMed

See these in context on the Tyrosine monograph →

Theanine 6 references
  1. Yokogoshi H, Kobayashi M. Hypotensive effect of gamma-glutamylethylamide in spontaneously hypertensive rats. Life Sci 1998;62:1065-8.
  2. Haskell, C. F., Kennedy, D. O., Milne, A. L., Wesnes, K. A., and Scholey, A. B. The effects of L-theanine, caffeine and their combination on cognition and mood. Biol.Psychol. 2008;77(2):113-122. PubMed
  3. Yokogoshi, H., Kato, Y., Sagesaka, Y. M., Takihara-Matsuura, T., Kakuda, T., and Takeuchi, N. Reduction effect of theanine on blood pressure and brain 5-hydroxyindoles in spontaneously hypertensive rats. Biosci.Biotechnol.Biochem. 1995;59(4):615-618. PubMed
  4. Lyon MR, Kapoor MP, Juneja LR. The effects of L-theanine (Suntheanine®) on objective sleep quality in boys with attention deficit hyperactivity disorder (ADHD): a randomized, double-blind, placebo-controlled clinical trial. Altern Med Rev. 2011;16(4):348-
  5. Hidese S, Ota M, Wakabayashi C, et al. Effects of chronic l-theanine administration in patients with major depressive disorder: an open-label study. Acta Neuropsychiatr 2017;29(2):72-9.
  6. Tsuchiya T, Honda H, Oikawa M, et al. Oral administration of the amino acids cystine and theanine attenuates the adverse events of S-1 adjuvant chemotherapy in gastrointestinal cancer patients. Int J Clin Oncol 2016;21(6):1085-90. PubMed

See these in context on the Theanine monograph →

Ashwagandha 32 references
  1. McGuffin M, Hobbs C, Upton R, Goldberg A, eds. American Herbal Products Association's Botanical Safety Handbook. Boca Raton, FL: CRC Press, LLC 1997.
  2. Upton R, ed. Ashwagandha Root (Withania somnifera): Analytical, quality control, and therapuetic monograph. Santa Cruz, CA: American Herbal Pharmacopoeia 2000:1-25.
  3. Davis L, Kuttan G. Effect of Withania somnifera on cyclophosphamide-induced urotoxicity. Cancer Lett 2000;148:9-17. PubMed
  4. Davis L, Kuttan G. Suppressive effect of cyclophosphamide-induced toxicity by Withania somnifera extract in mice. J Ethnopharmacol 1998;62:209-14. PubMed
  5. Mishra LC, Singh BB, Dagenais S. Scientific basis for the therapeutic use of Withania somnifera (ashwagandha): a review. Altern Med Rev 2000;5:334-46. DOI
  6. Andallu B, Radhika B. Hypoglycemic, diuretic and hypocholesterolemic effect of winter cherry (Withania somnifera, Dunal) root. Indian J Exp Biol 2000;38:607-9.
  7. Kulkarni RR, Patki PS, Jog VP, et al. Treatment of osteoarthritis with a herbomineral formulation: a double-blind, placebo-controlled, cross-over study. J Ethnopharmacol 1991;33:91-5. PubMed
  8. Ahumada F, Aspee F, Wikman G, Hancke J. Withania somnifera exract. Its effects on arterial blood pressure in anaesthetized dogs. Phytother Res 1991;5:111-14.
  9. Panda S, Kar A. Withania somnifera and Bauhinia purpurea in the regulation of circulating thyroid hormone concentrations in female mice. J Ethnopharmacol 1999;67:233-39. PubMed
  10. Panda S, Kar A. Changes in thyroid hormone concentrations after administration of ashwagandha root extract to adult male mice. J Pharm Pharmacol 1998;50:1065-68. PubMed
  11. Sehgal, V. N., Verma, P., and Bhattacharya, S. N. Fixed-drug eruption caused by ashwagandha (Withania somnifera): a widely used Ayurvedic drug. Skinmed. 2012;10(1):48-49.
  12. Agnihotri AP, Sontakke SD, Thawani VR, Saoji A, Goswami VS. Effects of Withania somnifera in patients of schizophrenia: a randomized, double blind, placebo controlled pilot trial study. Indian J Pharmacol. 2013;45(4):417-8. PubMed
  13. Biswal BM, Sulaiman SA, Ismail HC, Zakaria H, Musa KI. Effect of Withania somnifera (Ashwagandha) on the development of chemotherapy-induced fatigue and quality of life in breast cancer patients. Integr Cancer Ther. 2013;12(4):312-22.
  14. Sharma AK, Basu I, Singh S. Efficacy and safety of Ashwagandha root extract in subclinical hypothyroid patients: a double-blind, randomized placebo-controlled trial. J Altern Complement Med. 2018 Mar;24(3):243-248. PubMed
  15. Durg S, Bavage S, Shivaram SB. Withania somnifera (Indian ginseng) in diabetes mellitus: A systematic review and meta-analysis of scientific evidence from experimental research to clinical application. Phytother Res. 2020;34(5):1041-1059.
  16. Björnsson HK, Björnsson ES, Avula B, et al. Ashwagandha-induced liver injury: A case series from Iceland and the US Drug-Induced Liver Injury Network. Liver Int. 2020;40(4):825-829. PubMed
  17. Tharakan A, Shukla H, Benny IR, Tharakan M, George L, Koshy S. Immunomodulatory Effect of Withania somnifera (Ashwagandha) Extract-A Randomized, Double-Blind, Placebo Controlled Trial with an Open Label Extension on Healthy Participants. J Clin Med 2021;1 PubMed
  18. Ireland PJ, Hardy T, Burt AD, Donnelly MC. Drug-induced hepatocellular injury due to herbal supplement ashwagandha. J R Coll Physicians Edinb. 2021;51(4):363-365. PubMed
  19. Kamal HI, Patel K, Brdak A, Heffernan J, Ahmad N. Ashwagandha as a unique cause of thyrotoxicosis presenting with supraventricular tachycardia. Cureus. 2022 Mar 25;14(3):e23494. PubMed
  20. Suryawanshi G, Abdallah M, Thomson M, Desai N, Chauhan A, Lim N. Ashwagandha-Associated Acute Liver Failure Requiring Liver Transplantation. Am J Ther 2023;30(1):e80-e83. PubMed
  21. Pusec CM, Wolsky R, Llerena C, Sura P. A Case of Supplement-Induced Hepatitis. Cureus 2022;14(10):e30433. PubMed
  22. Ajgaonkar A, Jain M, Debnath K. Efficacy and Safety of Ashwagandha (Withania somnifera) Root Extract for Improvement of Sexual Health in Healthy Women: A Prospective, Randomized, Placebo-Controlled Study. Cureus 2022;14(10):e30787. PubMed
  23. Haron MH, Dale O, Martin K, et al. Evaluation of the Herb-Drug Interaction Potential of Commonly Used Botanicals on the US Market with Regard to PXR- and AhR-Mediated Influences on CYP3A4 and CYP1A2. J Diet Suppl 2022. PubMed
  24. Lubarska M, Halasinski P, Hryhorowicz S, et al. Liver Dangers of Herbal Products: A Case Report of Ashwagandha-Induced Liver Injury. Int J Environ Res Public Health 2023;20(5):3921. PubMed
  25. Tóth M, Benedek AE, Longerich T, Seitz HK. Ashwagandha-induced acute liver injury: A case report. Clin Case Rep 2023;11(3):e7078.
  26. Bokan G, Glamocanin T, Mavija Z, et al. Herb-Induced Liver Injury by Ayurvedic Ashwagandha as Assessed for Causality by the Updated RUCAM: An Emerging Cause. Pharmaceuticals (Basel) 2023;16(8):1129. PubMed
  27. Patel PA, Sanborn E, Then R, Williams DM. Recurrent Reversible Cerebral Vasoconstriction Syndrome: A Report of Two Cases. Cureus 2023;15(8):e42992. PubMed
  28. Majeed M, Nagabhushanam K, Murali A, Vishwanathan DT, Mamidala RV, Mundkur L. A Standardized Withania somniferra (Linn.) Root Extract with Piperine Alleviates the Symptoms of Anxiety and Depression by Increasing Serotonin Levels: A Double-Blind, Randomize
  29. Philips CA, Valsan A, Theruvath AH, et al. Ashwagandha-induced liver injury-A case series from India and literature review. Hepatol Commun 2023;7(10):e0270. PubMed
  30. Hayashi M, Hamada H, Azuma SI, Hayashi K. Painless Thyroiditis by Withania somnifera (Ashwagandha). Cureus 2024;16(3):e55352. PubMed
  31. Vazirani S, Kothari A, Fujimoto J, Gomez M. Supplements Are Not a Synonym for Safe: Suspected Liver Injury From Ashwagandha. Fed Pract 2023;40(9):315-319. PubMed
  32. Patel M, Newell R, Hillier M, Ramalingam R. Herbal remedies as a potential cause of hypoadrenalism. Br J Hosp Med (Lond) 2024;85(6):1-4. PubMed

See these in context on the Ashwagandha monograph →

Brewer's Yeast 6 references
  1. Blumenthal M, ed. The Complete German Commission E Monographs: Therapeutic Guide to Herbal Medicines. Trans. S. Klein. Boston, MA: American Botanical Council, 1998.
  2. Lewis SJ, Freedman AR. Review article: the use of biotherapeutic agents in the prevention and treatment of gastrointestinal disease. Aliment Pharmacol Ther 1998;12:807-22. PubMed
  3. Bahijiri, S. M., Mira, S. A., Mufti, A. M., and Ajabnoor, M. A. The effects of inorganic chromium and brewer's yeast supplementation on glucose tolerance, serum lipids and drug dosage in individuals with type 2 diabetes. Saudi.Med.J. 2000;21(9):831-837. DOI
  4. Schrauzer, G. N. and de, Vroey E. Effects of nutritional lithium supplementation on mood. A placebo-controlled study with former drug users. Biol.Trace Elem.Res. 1994;40(1):89-101. PubMed
  5. Gayathri R, Aruna T, Malar S, Shilpa B, Dhanasekar KR. Efficacy of Saccharomyces cerevisiae CNCM I-3856 as an add-on therapy for irritable bowel syndrome. Int J Colorectal Dis. 2020;35(1):139-145. PubMed
  6. Mourey F, Decherf A, Jeanne JF, et al. Saccharomyces cerevisiae I-3856 in irritable bowel syndrome with predominant constipation. World J Gastroenterol 2022;28(22):2509-2522.

See these in context on the Brewer's Yeast monograph →

Manganese 21 references
  1. Hansten PD, Horn JR. Hansten and Horn's Drug Interactions Analysis and Management. Vancouver, CAN:Appl Therapeut, 1999.
  2. Barrington WW, Angle CR, Willcockson NK, et al. Autonomic function in manganese alloy workers. Environ Res 1998;78:50-8. PubMed
  3. Hauser RA, Zesiewicz TA, Martinez C, et al. Blood manganese correlates with brain magnetic resonance imaging changes in patients with liver disease. Can J Neurol Sci 1996;23:95-8. PubMed
  4. Food and Nutrition Board, Institute of Medicine. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington, DC: National Academy Press, 2002.
  5. Lee JW. Manganese intoxication. Arch Neurol 2000;57:597-9.. PubMed
  6. Powers KM, Smith-Weller T, Franklin GM, et al. Parkinson's disease risks associated with dietary iron, manganese, and other nutrient intakes. Neurology 2003;60:1761-6.. PubMed
  7. McMillan, D. E. A brief history of the neurobehavioral toxicity of manganese: some unanswered questions. Neurotoxicology 1999;20(2-3):499-507.
  8. Gerber, G. B., Leonard, A., and Hantson, P. Carcinogenicity, mutagenicity and teratogenicity of manganese compounds. Crit Rev Oncol Hematol. 2002;42(1):25-34. PubMed
  9. Jiang, Y. and Zheng, W. Cardiovascular toxicities upon manganese exposure. Cardiovasc.Toxicol 2005;5(4):345-354. PubMed
  10. Mehta, R. and Reilly, J. J. Manganese levels in a jaundiced long-term total parenteral nutrition patient: potentiation of haloperidol toxicity? Case report and literature review. JPEN J Parenter.Enteral Nutr 1990;14(4):428-430. PubMed
  11. Nemery, B. Metal toxicity and the respiratory tract. Eur Respir.J 1990;3(2):202-219. DOI
  12. Vanek VW, Borum P, Buchman A, et al. A.S.P.E.N. position paper: recommendations for changes in commercially available parenteral multivitamin and multi-trace element products. Nutr Clin Pract. 2012;27:440-491.doi: 10.1177/0884533612446706 PubMed
  13. Schuh MJ. Possible Parkinson's disease induced by chronic manganese supplement ingestion. Consult Pharm. 2016;31(12):698-703. doi: 10.4140/TCP.n.2016.698. PubMed
  14. Baker B, Ali A, Isenring L. Recommendations for manganese supplementation to adult patients receiving long-term home parenteral nutrition: an analysis of the supporting evidence. Nutr Clin Pract 2016;31(2):180-5. doi: 10.1177/0884533615591600. PubMed
  15. Ho CSH, Ho RCM, Quek AML. Chronic manganese toxicity associated with voltage-gated potassium channel complex antibodies in a relapsing neuropsychiatric disorder. Int J Environ Res Public Health 2018;15(4). pii: E783. doi: 10.3390/ijerph15040783. PubMed
  16. Yamamoto M, Sakurai K, Eguchi A, et al.; Japan Environment and Children's Study Group: Association between blood manganese level during pregnancy and birth size: the Japan environment and children's study (JECS). Environ Res 2019;172:117-26. PubMed
  17. Li D, Ge X, Liu Z, et al. Association between long-term occupational manganese exposure and bone quality among retired workers. Environ Sci Pollut Res Int 2020;27(1):482-9. PubMed
  18. Martin KV, Sucharew H, Dietrich KN, et al. Co-exposure to manganese and lead and pediatric neurocognition in East Liverpool, Ohio. Environ Res 2021;202:111644. PubMed
  19. Racette BA, Nelson G, Dlamini WW, et al. Depression and anxiety in a manganese-exposed community. Neurotoxicology 2021;85:222-33. PubMed
  20. Ruiz-Azcona L, Fernández-Olmo I, Expósito A, et al. Impact of environmental airborne manganese exposure on cognitive and motor functions in adults: a systematic review and meta-analysis. Int J Environ Res Public Health 2021;18(8):4075. PubMed
  21. Uyar E, Gurkas E, Aksu AU, et al. Can therapeutic plasma exchange be life-saving in life-threatening manganese intoxication?. Transfus Apher Sci 2022;61(4):103417. PubMed

See these in context on the Manganese monograph →

Copper 11 references
  1. Murry JJ, Healy MD. Drug-mineral interactions: a new responsibility for the hospital dietician. J Am Diet Assoc 1991;91:66-73.
  2. Campbell IA, Elmes PC. Ethambutol and the eye: zinc and copper (letter). Lancet 1975;2:711. DOI
  3. Segal S, Kaminski S. Drug-nutrient interactions. American Druggist 1996 Jul;42-8.
  4. Kozak SF, Inderlied CB, Hsu HY, et al. The role of copper on ethambutol's antimicrobial action and implications for ethambutol-induced optic neuropathy. Diag Microbiol Infect Dis 1998;30:83-7. PubMed
  5. Food and Nutrition Board, Institute of Medicine. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington, DC: National Academy Press, 2002.
  6. Cantilena LR, Klaassen CD. The effect of chelating agents on the excretion of endogenous metals. Toxicol Appl Pharmacol 1982;63:344-50.
  7. Babic Z, Tariba B, Kovacic J, Pizent A, Varnai VM, Macan J. Relevance of serum copper elevation induced by oral contraceptives: a meta-analysis. Contraception. 2013 Jun;87(6):790-800. PubMed
  8. Qui Q, Zhang F, Zhu W, Wu J, Liang M. Copper in diabetes mellitus: a meta-analysis and systematic review of plasma and serum studies. Biol Trace Elem Res 2017;177(1):53-63.
  9. Walker-Smith PK, Keith DJ, Kennedy CT, Sansom JE. Allergic contact dermatitis caused by copper. Contact Dermatitis 2016;75(3):186-7. PubMed
  10. Gallentine A. Third-degree burn on the neuropathic lower extremity in a patient with diabetes while wearing a copper-containing compression sock: a case report. Wound Manag Prev 2021;67(12):26-29. DOI
  11. Chung KJ, Chin YM, Wong MS, Sanmugam A, Singaravel S, Nah SA. Effectiveness of table salt versus copper sulphate in treating umbilical granuloma: A pilot randomized controlled trial. J Pediatr Surg 2022;57(2):261-265. PubMed

See these in context on the Copper monograph →

Licorice 92 references
  1. Farese RV Jr, Biglieri EG, Shackleton CH, et al. Licorice-induced hypermineralocorticoidism. N Engl J Med 1991;325:1223-7. PubMed
  2. Sigurjonsdottir HA, Ragnarsson J, Franzson L, Sigurdsson G. Is blood pressure commonly raised by moderate consumption of liquorice? J Hum Hypertens 1995;9:345-8.
  3. Armanini D, Lewicka S, Pratesi C, et al. Further studies on the mechanism of the mineralocorticoid action of licorice in humans. J Endocrinol Invest 1996;19:624-9. PubMed
  4. Zhang YD, Lorenzo B, Reidenberg MM. Inhibition of 11 beta hydroxysteroid dehydrogenase obtained from guinea pig kidney by furosemide, naringenin and some other compounds. J Steroid Biochem Mol Biol 1994;49:81-5.
  5. Strandberg TE, Jarvenpaa AL, Vanhanen H, McKeigue PM. Birth outcome in relation to licorice consumption during pregnancy. Am J Epidemiol 2001;153:1085-8. PubMed
  6. Sigurjonsdottir HA, Franzson L, Manhem K, et al. Liquorice-induced rise in blood pressure: a linear dose-response relationship. J Hum Hypertens 2001;15:549-52. PubMed
  7. Amato P, Christophe S, Mellon PL. Estrogenic activity of herbs commonly used as remedies for menopausal symptoms. Menopause 2002;9:145-50. PubMed
  8. Kent UM, Aviram M, Rosenblat M, Hollenberg PF. The licorice root derived isoflavan glabridin inhibits the activities of human cytochrome P450S 3A4, 2B6, and 2C9. Drug Metab Dispos 2002;30:709-15.. PubMed
  9. Yoshida S, Takayama Y. Licorice-induced hypokalemia as a treatable cause of dropped head syndrome. Clin Neurol Neurosurg 2003;105:286-7.. PubMed
  10. Strandberg TE, Andersson S, Jarvenpaa AL, et al. Preterm birth and licorice consumption during pregnancy. Am J Epidemiol 2002;156:803-5.. PubMed
  11. Hussain RM. The sweet cake that reaches parts other cakes can't! Postgrad Med J 2003;79:115-6.. PubMed
  12. Morris DJ, Davis E, Latif SA. Licorice, tobacco chewing, and hypertension. N Engl J Med 1990;322:849-50. PubMed
  13. Quinkler M, Stewart PM. Hypertension and the cortisol-cortisone shuttle. J Clin Endocrinol Metab 2003;88:2384-92. PubMed
  14. Westman EC, Guthrie GP. Licorice, tobacco chewing, and hypertension. N Engl J Med 1990;322:850. PubMed
  15. Mu Y, Zhang J, Zhang S, et al. Traditional Chinese medicines Wu Wei Zi (Schisandra chinensis Baill) and Gan Cao (Glycyrrhiza uralensis Fisch) activate pregnane X receptor and increase warfarin clearance in rats. J Pharmacol Exp Ther 2006;316:1369-77. PubMed
  16. Yasue H, Itoh T, Mizuno Y, Harada E. Severe hypokalemia, rhabdomyolysis, muscle paralysis, and respiratory impairment in a hypertensive patient taking herbal medicines containing licorice. Intern Med 2007;46:575-8. PubMed
  17. Brayley J, Jones J. Life-threatening hypokalemia associated with excessive licorice ingestion (letter). Am J Psychiatry 1994;151:617-8. PubMed
  18. de Klerk GJ, Nieuwenhuis G, Beutler JJ. Hypokalaemia and hypertension associated with use of liquorice flavoured chewing gum. BMJ 1997;314:731-2.
  19. Dellow EL, Unwin RJ, Honour JW. Pontefract cakes can be bad for you: refractory hypertension and liquorice excess. Nephol Dial Transplant 1999;14:218-20. PubMed
  20. Elinav E, Chajek-Shaul T. Licorice consumption causing severe hypokalemic paralysis. Mayo Clin Proc 2003;78:767-8. PubMed
  21. Eriksson JW, Carlberg B, Hillom V. Life-threatening ventricular tachycardia due to liquorice-induced hypokalemia. J Intern Med 1999;245:307-10.
  22. Janse A, van Iersel M, Hoefnagels WH, Olde Rikker MG. The old lady who liked liquorice: hypertension due to chronic intoxication in a memory-impaired patient. Neth J Med 2005;63:149-50.
  23. Lin SH, Yang SS, Chau T, Halperin ML. An unusual cause of hypokalemic paralysis: chronic licorice ingestion. Am J Med Sci 2003;325:153-6. PubMed
  24. van den Bosch AE, van der Klooster JM, Zuidgeest DM, et al. Severe hypokalemic paralysis and rhabdomyolysis due to ingestion of liquorice. Neth J Med 2005;63:146-8.
  25. van Uum SH. Liquorice and hypertension. Neth J Med 2005;63:119-20.
  26. Russo S, Mastropasqua M, Mosetti MA, et al. Low doses of liquorice can induce hypertension encephalopathy. Am J Nephrol 2000;20:145-8. PubMed
  27. Stormer FC, Reistad R, Alexander J. Glycyrrhizic acid in liquorice - evaluation of health hazard. Food Chem Toxicol 1993;31:303-12. PubMed
  28. Sontia B, Mooney J, Gaudet L, Touyz RM. Pseudohyperaldosteronism, liquorice, and hypertension. J Clin Hypertens (Greenwich) 2008;10:153-7. PubMed
  29. Francini-Pesenti F, Puato M, Piccoli A, Brocadello F. Liquorice-induced hypokalaemia and water retention in the absence of hypertension. Phytother Res 2008;22:563-5. PubMed
  30. Lapi F, Gallo E, Bernasconi S, et al. Myopathies associated with red yeast rice and liquorice: spontaneous reports from the Italian Surveillance System of Natural Health Products. Br J Clin Pharmacol 2008;66:572-4. PubMed
  31. Chen MF, Shimada F, Kato H, Yano S, Kanaoka M. Effect of glycyrrhizin on the pharmacokinetics of prednisolone following low dosage of prednisolone hemisuccinate. Endocrinol Jpn 1990;37:331-41. PubMed
  32. Teelucksingh S, Mackie AD, Burt D, McIntyre MA, Brett L, Edwards CR. Potentiation of hydrocortisone activity in skin by glycyrrhetinic acid. Lancet 1990;335(8697):1060-3. PubMed
  33. Heidemann HT, Kreuzfelder E. Hypokalemic rhabdomyolysis with myoglobinuria due to licorice ingestion and diuretic treatment. Klin Wochenschr 1983;61:303-5. PubMed
  34. Hukkanen J, Ukkola O, Savolainen MJ. Effects of low-dose liquorice alone or in combination with hydrochlorothiazide on the plasma potassium in healthy volunteers. Blood Press 2009;18:192-5. PubMed
  35. Bisogni V, Rossi GP, Calò LA. Apparent mineralcorticoid excess syndrome, an often forgotten or unrecognized cause of hypokalemia and hypertension: case report and appraisal of the pathophysiology. Blood Press. 2014 Jun;23(3):189-92. PubMed
  36. Dehours E, Vallé B, Rougé-Bugat ME, Florent B, Bounes V, Franchitto N. Suspected hypokalaemia following liquorice ingestion on board ship. J Telemed Telecare. 2013 Jun;19(4):227-8. PubMed
  37. Kormann R, Languille E, Amiot HM, Hertig A. Dying for a cup of tea. BMJ Case Rep. 2012 Oct 19;2012. PubMed
  38. Panduranga P, Al-Rawahi N. Licorice-induced severe hypokalemia with recurrent torsade de pointes. Ann Noninvasive Electrocardiol. 2013 Nov;18(6):593-6. PubMed
  39. Räikkönen K, Seckl JR, Heinonen K, Pyhälä R, Feldt K, Jones A, Pesonen AK, Phillips DI, Lahti J, Järvenpää AL, Eriksson JG, Matthews KA, Strandberg TE, Kajantie E. Maternal prenatal licorice consumption alters hypothalamic-pituitary-adrenocortical axis fu
  40. Robles BJ, Sandoval AR, Dardon JD, Blas CA. Lethal liquorice lollies (liquorice abuse causing pseudohyperaldosteronism). BMJ Case Rep. 2013 Sep 19;2013. PubMed
  41. Chamberlain, J. J. and Abolnik, I. Z. Pulmonary edema following a licorice binge. West J Med 1997;167(3):184-185.
  42. Barrella, M., Lauria, G., Quatrale, R., and Paolino, E. Hypokaliemic rhabdomyolysis associated with liquorice ingestion: report of an atypical case. Ital.J Neurol.Sci 1997;18(4):217-220. PubMed
  43. Fugh-Berman, A. Herb-drug interactions. Lancet 2000;355(9198):134-138. PubMed
  44. Hasegawa, J., Suyama, Y., Kinugawa, T., Morisawa, T., and Kishimoto, Y. Echocardiographic findings of the heart resembling dilated cardiomyopathy during hypokalemic myopathy due to licorice-induced pseudoaldosteronism. Cardiovasc.Drugs Ther 1998;12(6):59 PubMed
  45. van Rossum, T. G., Vulto, A. G., Hop, W. C., Brouwer, J. T., Niesters, H. G., and Schalm, S. W. Intravenous glycyrrhizin for the treatment of chronic hepatitis C: a double-blind, randomized, placebo-controlled phase I/II trial. J Gastroenterol Hepatol 199 PubMed
  46. Lozano, P., Flores, D., Martinez, S., Artigues, I., Rimbau, E. M., and Gomez, F. Upper limb ischemia induced by chronic licorice ingestion. J Cardiovasc.Surg (Torino) 2000;41(4):631-632.
  47. Brouwers, A. J. and van der, Meulen J. ['Licorice hypertension' also caused by licorice tea]. Ned.Tijdschr Geneeskd. 4-14-2001;145(15):744-747.
  48. van Rossum, T. G., Vulto, A. G., Hop, W. C., and Schalm, S. W. Glycyrrhizin-induced reduction of ALT in European patients with chronic hepatitis C. Am J Gastroenterol 2001;96(8):2432-2437. PubMed
  49. Sigurjonsdottir, H. A., Manhem, K., Axelson, M., and Wallerstedt, S. Subjects with essential hypertension are more sensitive to the inhibition of 11 beta-HSD by liquorice. J Hum Hypertens 2003;17(2):125-131.
  50. Shintani, S., Murase, H., Tsukagoshi, H., and Shiigai, T. Glycyrrhizin (licorice)-induced hypokalemic myopathy. Report of 2 cases and review of the literature. Eur Neurol 1992;32(1):44-51. PubMed
  51. Chen, M. F., Shimada, F., Kato, H., Yano, S., and Kanaoka, M. Effect of oral administration of glycyrrhizin on the pharmacokinetics of prednisolone. Endocrinol Jpn 1991;38(2):167-174. PubMed
  52. Lee, C. K., Park, K. K., Lim, S. S., Park, J. H., and Chung, W. Y. Effects of the licorice extract against tumor growth and cisplatin-induced toxicity in a mouse xenograft model of colon cancer. Biol Pharm Bull 2007;30(11):2191-2195. PubMed
  53. Isaia, G. C., Pellissetto, C., Ravazzoli, M., and Tamone, C. Acute adrenal crisis and hypercalcemia in a patient assuming high liquorice doses. Minerva Med 2008;99(1):91-94.
  54. Bocker, D. and Breithardt, G. [Induction of arrhythmia by licorice abuse]. Z Kardiol 1991;80(6):389-391.
  55. Tacconi, P., Paribello, A., Cannas, A., and Marrosu, M. G. Carpal tunnel syndrome triggered by excessive licorice consumption. J Peripher.Nerv.Syst. 2009;14(1):64-65. PubMed
  56. Tu, J. H., He, Y. J., Chen, Y., Fan, L., Zhang, W., Tan, Z. R., Huang, Y. F., Guo, D., Hu, D. L., Wang, D., and Hong-Hao Zhou. Effect of glycyrrhizin on the activity of CYP3A enzyme in humans. Eur J Clin Pharmacol 2010;66(8):805-810. PubMed
  57. Goultschin, J., Palmon, S., Shapira, L., Brayer, L., and Gedalia, I. Effect of glycyrrhizin-containing toothpaste on dental plaque reduction and gingival health in humans. A pilot study. J Clin Periodontol 1991;18(3):210-212. PubMed
  58. Scali, M., Pratesi, C., Zennaro, M. C., Zampollo, V., and Armanini, D. Pseudohyperaldosteronism from liquorice-containing laxatives. J Endocrinol Invest 1990;13(10):847-848. PubMed
  59. Chatterjee, N., Domoto-Reilly, K., Fecci, P. E., Schwamm, L. H., and Singhal, A. B. Licorice-associated reversible cerebral vasoconstriction with PRES. Neurology 2010;75(21):1939-1941. PubMed
  60. Imtiaz, K. E. Sweet root, bitter pill: liquorice-induced hyperaldosteronism. QJM 2011;104(12):1093-1095. PubMed
  61. van Beers, E. J., Stam, J., and van den Bergh, W. M. Licorice consumption as a cause of posterior reversible encephalopathy syndrome: a case report. Crit Care 2011;15(1):R64. PubMed
  62. MacKenzie, M. A., Hoefnagels, W. H., Jansen, R. W., Benraad, T. J., and Kloppenborg, P. W. The influence of glycyrrhetinic acid on plasma cortisol and cortisone in healthy young volunteers. J Clin Endocrinol Metab 1990;70(6):1637-1643. PubMed
  63. Bardhan, K. D., Cumberland, D. C., Dixon, R. A., and Holdsworth, C. D. Clinical trial of deglycyrrhizinised liquorice in gastric ulcer. Gut 1978;19(9):779-782. PubMed
  64. Koster, M. and David, G. K. Reversible severe hypertension due to licorice ingestion. N Engl J Med 1968;278(25):1381-1383. PubMed
  65. Corse, F. M., Galgani, S., Gasparini, C., Giacanelli, M., and Piazza, G. Acute hypokalemic myopathy due to chronic licorice ingestion: report of a case. Ital J Neurol Sci 1983;4(4):493-497. PubMed
  66. Berlango Jimenez A., Jimenez Murillo L., Montero Perez F. J., Munoz Avila J. A., Torres Murillo J., and Calderon de la Barca Gazquez J. M. [Acute rhabdomyolysis and tetraparesis secondary to hypokalemia due to ingested licorice]. An Med Interna 1995;12(1)
  67. Bernardi, M., D'Intino, P. E., Trevisani, F., Cantelli-Forti, G., Raggi, M. A., Turchetto, E., and Gasbarrini, G. Effects of prolonged ingestion of graded doses of licorice by healthy volunteers. Life Sci 1994;55(11):863-872. PubMed
  68. van der Zwan A. Hypertension encephalopathy after liquorice ingestion. Clin Neurol Neurosurg 1993;95(1):35-37. PubMed
  69. Werner, S., Brismar, K., and Olsson, S. Hyperprolactinaemia and liquorice. Lancet 2-10-1979;1(8111):319.
  70. Nishioka, K. and Seguchi, T. Contact allergy due to oil-soluble licorice extracts in cosmetic products. Contact Dermatitis 1999;40(1):56. PubMed
  71. Yoshino T, Yanagawa T, Watanabe K. Risk factors for pseudoaldosteronism with rhabdomyolysis caused by consumption of drugs containing licorice and differences between incidence of these conditions in Japan and other countries: case report and literature r
  72. Li G, Simmler C, Chen L, et al. Cytochrome P450 inhibition by three licorice species and fourteen licorice constituents. Eur J Pharm Sci. 2017;109:182-190. PubMed
  73. Li J, Fan X, Wang Q. Hypertensive crisis with 2 target organ impairment induced by glycyrrhizin: a case report. Medicine (Baltimore) 2018;97(11):e0073. PubMed
  74. Foster CA, Church KS, Poddar M, Van Uum SH, Spaic T. Licorice-induced hypertension: a case of pseudohyperaldosteronism due to jelly bean ingestion. Postgrad Med 2017;129(3):329-31. PubMed
  75. Gallacher SD, Tsokolas G, Dimitropoulos I. Liquorice-induced apparent mineralocorticoid excess presenting in the emergency department. Clin Med (Lond) 2017;17(1):43-5. PubMed
  76. Dai DW, Singh I, Hershman JM. Lozenge-induced hypermineralcorticoid state--a unique case of licorice lozenges resulting in hypertension and hypokalemia. J Clin Hypertens (Greenwich) 2016;18(2):159-60.
  77. O'Connell K, Kinsella J, McMahon C, Holian J, O'Riordan S. Posterior reversible encephalopathy syndrome (PRES) associated with liquorice consumption. Ir J Med Sci 2016;185(4):945-7. PubMed
  78. Hataya Y, Oba A, Yamashita T, Komatsu Y. Hyponatremia in an elderly patient due to isolated hypoaldosteronism occurring after licorice withdrawal. Intern Med 2017;56(2):175-9. PubMed
  79. Ha Y, Wang T, Li J, et al. Herb-Drug Interaction Potential of Licorice Extract and Paclitaxel: A Pharmacokinetic Study in Rats. Eur J Drug Metab Pharmacokinet. 2020;45(2):257-264. PubMed
  80. Edelman ER, Butala NM, Avery LL, Lundquist AL, Dighe AS. Case 30-2020: A 54-Year-Old Man with Sudden Cardiac Arrest. N Engl J Med. 2020;383(13):1263-1275. PubMed
  81. Wang H, Dong L, Qu F, et al. Effects of glycyrrhizin on the pharmacokinetics of nobiletin in rats and its potential mechanism. Pharm Biol. 2020 Dec;58(1):352-356. PubMed
  82. Attou R, Redant S, Honore PM, Preseau T, Hantson P, De Bels D. Liquorice intoxication can lead to cardiac arrest! Case Rep Emerg Med. 2020;2020:3727682. PubMed
  83. Benge E, Shah P, Yamaguchi L, Josef V. Trick or Treat? Licorice-Induced Hypokalemia: A Case Report. Cureus 2020;12(11):e11656. PubMed
  84. Abe K, Higurashi T, Takahashi M, et al. Concomitant Use of High-dose Methotrexate and Glycyrrhizin Affects Pharmacokinetics of Methotrexate, Resulting in Hepatic Toxicity. In Vivo 2021;35(4):2163-2169. PubMed
  85. Awad N, Makar G, Burroughs V, Ravi P, Burroughs SR. Licorice-induced apparent mineralocorticoid excess causing persistent hypertension and hypokalemia. Acta Endocrinol (Buchar) 2020;16(4):508-510. PubMed
  86. Patel P, Aknouk M, Dawson A, et al. How Much Is Too Much? Exploring Pseudohyperaldosteronism in Glycyrrhizic Acid Toxicity From Chronic Licorice Root Consumption. Cureus 2021;13(7):e16454. PubMed
  87. Fan ZJ, Liu JM, Li XX, et al. Glycyrrhizin-Induced Pseudohyperaldosteronism: A Case Report. Chin J Integr Med 2022. PubMed
  88. Gatica-Ortega ME, Pastor-Nieto MA. Allergic contact dermatitis to Glycyrrhiza inflata root extract in an anti-acne cosmetic product. Contact Dermatitis 2021;85(4):454-455.
  89. Wang JB, Huang A, Wang Y, et al. Corticosteroid plus glycyrrhizin therapy for chronic drug- or herb-induced liver injury achieves biochemical and histological improvements: a randomised open-label trial. Aliment Pharmacol Ther 2022;55(10):1297-1310. PubMed
  90. Puaratanaarunkon T, Washrawirul C, Chuenboonngarm N, Noppakun N, Asawanonda P, Kumtornrut C. Efficacy and safety of a facial serum containing snail secretion filtrate, Calendula officinalis, and Glycyrrhiza glaba root extract in the treatment of maskne: A
  91. Haron MH, Dale O, Martin K, et al. Evaluation of the Herb-Drug Interaction Potential of Commonly Used Botanicals on the US Market with Regard to PXR- and AhR-Mediated Influences on CYP3A4 and CYP1A2. J Diet Suppl 2022. PubMed
  92. Han EJ, Park JS. Lethal Arrhythmia Induced by Licorice. J Korean Med Sci 2023;38(12):e107. PubMed

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DISCLAIMER: Currently this does not check for drug-drug interactions. This is not an all-inclusive comprehensive list of potential interactions and is for informational purposes only. Not all interactions are known or well-reported in the scientific literature, and new interactions are continually being reported. Input is needed from a qualified healthcare provider including a pharmacist before starting any therapy. Application of clinical judgment is necessary.

© 2021 Therapeutic Research Center, LLC

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