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Dietary supplement

L-Theanine Ingredients & Drug Interactions

by Hard Rhino

L-Theanine label
See full label image
Powder Category: Non-nutrient/non-botanical
Most serious interaction: Moderate
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: Moderate

L-Theanine is a dietary supplement by Hard Rhino with 1 active ingredient. Its ingredients are commonly taken for anxiety and stress, relaxation and calm, sleep support.Based on those ingredients, 565 medications have a known interaction with it, the most serious rated moderate. The ingredients most likely to interact are 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 Hard Rhino

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

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HelloPharmacist Scorecard of L-Theanine by Hard Rhino

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 Aug 13, 2026

What’s inside

Full disclosure
Ingredient Transparency · database check
Full

Every active ingredient lists its own amount on the label.

Why this rating?
  • The label discloses an exact amount for 1 of its 1 active ingredient.
  • No proprietary blends here — you can verify the dose of every single component.

This is a single-ingredient product: L-Theanine, an amino acid found naturally in tea leaves. L-Theanine is thought to promote relaxation and support mental clarity without causing drowsiness, though the science on exactly how it works in the brain is still being studied.

The product contains no inactive ingredients or fillers.

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

This product doesn't appear to be marketed for a specific use, so we graded Theanine's overall clinical evidence instead.

Moderate

Some clinical evidence supports Theanine for:

Why this rating?
  • We looked at the product name, claims, and label statements and couldn't find a stated purpose to grade.
  • Since the label doesn't commit to one use, we graded the ingredient's overall clinical evidence instead.
  • On file: Cognitive function — rated "Possibly Effective" (Natural Medicines).

The evidence supports L-Theanine as possibly effective for supporting cognitive function. For other uses—age-related cognitive decline, Alzheimer's disease, generalized anxiety disorder, obsessive-compulsive disorder, and cancer—the data we hold shows insufficient reliable evidence to rate whether it works.

If you're considering L-Theanine for any of these purposes, talk with your doctor about what the current research shows and whether it's a fit for your situation.

The evidence, ingredient by ingredient Theanine

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 1 of the 1 matched ingredient.
  • Pregnancy & breastfeeding safety ratings cover 1 of 1.
  • General safety write-ups exist for 1 of 1.
  • Remember: this measures how much safety information exists. Thin data is not the same as being safe.

L-Theanine is generally well tolerated in healthy adults when used short-term, though long-term safety hasn't been thoroughly studied. The most common side effects reported are headaches, drowsiness, and changes to sleep patterns—including longer sleep duration and more vivid dreams.

One case of facial tics was reported in a child taking a high dose, but the tics stopped when the supplement was discontinued, and the child had a history of tics unrelated to the supplement. The safety data available advises against use during pregnancy and breastfeeding because there isn't enough information to know whether it's safe for the baby.

If you're pregnant, planning to become pregnant, or breastfeeding, talk with your doctor or pharmacist before taking this supplement.

Side effects, ingredient by ingredient Theanine

Meds to double-check

Moderate interaction found
Known Interaction Concern · database check
Moderate identified

The most serious documented interaction for these ingredients is Moderate. Check your medications for a personalized result.

Why this rating?
  • 1 of the 1 matched ingredient can interact with medications — Theanine.
  • The most serious interaction on file is rated Moderate.
  • For scale: 565 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 you start, double-check L-Theanine with your doctor or pharmacist if you take blood pressure medications—the most serious interaction risk here. Also flag any sedating drugs (sleep aids, anxiety meds, pain relievers that make you drowsy).

Serotonergic drugs (antidepressants) are a lower-priority concern based on the evidence, but it doesn't hurt to mention it.

Check your own medication Run your meds through the checker above

The bottom line

Scorecard at a glanceFully disclosed formula with some supporting evidence behind its ingredients' uses. Moderate medication interactions have been identified, and safety information is well characterized.

L-Theanine may help with focus and mental clarity if the research bears out for your needs, but it's best suited for otherwise healthy adults taking it short-term. If you're on blood pressure medication or any sedating drugs, check with your doctor or pharmacist first—the interactions are real and worth confirming won't affect your treatment.

Pregnant or breastfeeding? Skip it until you've talked things through with your healthcare provider.

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

Assessment coverage: 1 of 1 active ingredient matched to our full ingredient reviews (monographs). Based on the product label dated Apr 25, 2017.

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 Hard Rhino
Barcode (UPC) 818132471997
Net contents 125 Gram(s); 4.4 Oz(s)
Market status On market
Date entered into DSLD Apr 25, 2017
DSLD ID 72644
Product type Non-nutrient/non-botanical
Supplement form Powder
Dietary claims / uses All Other, Structure/Function
Intended target group(s) Adult (18 - 50 Years), Gluten Free, Dairy Free
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 Hard Rhino, 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:
200 mg
Maximum serving Sizes:
200 mg
Servings per container
625
UPC/BARCODE
818132471997
IngredientAmount% DV
L-Theanine200 mg--

Other ingredients: None

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.
Formulation

No added fillers

Allergens: This product contains no soy, dairy, dairy byproducts, eggs, shellfish, wheat, gluten, tree nuts, or sesame seeds.

This is a non-GMO ingredient.

General Statements

Only pure ingredients

Pure powder

Suggested/Recommended/Usage/Directions

Suggested Use: As a dietary supplement, take 200 mg with 6-8 ounces of water or suitable beverage. Taken 1-2 times daily, or as directed by a qualified health professional. A micro scale is recommended for accurate measuring.

1 Carefully measure out suggested serving size using a microscale. 2 Add to preferred beverage. 3 Mix well. 4 Drink within 10-15 minutes. How to use

Storage: Store in a cool, dry place. Re-seal zipper immediately after use to preserve freshness.

FDA Disclaimer Statement

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

Precautions

Warning: Keep out of the reach of children. Do not take this or any other supplement if under the age of 18, pregnant or nursing a baby, or if you have any known or suspected medical conditions and/or taking prescription drug(s) or OTC medication(s).

Do not take this or any other supplement if under the age of 18, pregnant or nursing a baby, or if you have any known or suspected medical conditions and/or taking prescription drug(s) or OTC medication(s).

Always consult with a qualified health physician before taking any new dietary supplement.

Do not use or consume if pressure seal is broken.

Do not use or consume if seal is broken.

Seals/Symbols

Lab tested for purity and quality

Packaged in USA

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 Hard Rhino 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 Hard Rhino

This is the 1 active ingredient this product is made of. Select it to open its full monograph.

Serving size200 mg Dosage formPowder Servings per container625 Amounts shown are per serving.

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

Other (inactive) ingredients: None. These complete the product’s ingredient list but are not active constituents.

Interaction report

L-Theanine by Hard Rhino 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
565Drugs
172 Moderate 393 Minor

Ingredients driving the most interactions

L-Theanine 565

Individual Drug Interactions

The ingredients in L-Theanine interact with 565 drugs. Click any drug to see the details.

1 of the 1 ingredient in L-Theanine interact with drugs. Each result below shows which ingredient is responsible. L-Theanine

Each ingredient & the kinds of drugs it affects

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

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
The maker

Brand information

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

Hard Rhino

See all Hard Rhino products
Name
Guardian Wholesale
Street Address
1607 West Whispering Wind Drive
City
Phoenix
State
AZ
ZipCode
85085
Phone Number
(866) 961-8378
Web Address
HardRhino.com
Pharmacist Counseling Corner

L-Theanine by Hard Rhino: Common Questions

Does L-Theanine by Hard Rhino interact with any medications?
Yes. Based on its ingredients, L-Theanine has a known interaction with 565 medications. Use the checker to see how it interacts with a specific drug.
How can one product interact with so many drugs?
L-Theanine contains a single active ingredient, and that one ingredient can interact with many different medications on its own. We check it against each medication and show the mechanism 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.
Will L-Theanine make me drowsy?
L-Theanine is designed to promote relaxation without making you sleepy, but some people do report drowsiness as a side effect. Others have noticed longer sleep duration and more vivid dreams. Start with a lower dose to see how it affects you personally.
Can I take L-Theanine while pregnant or breastfeeding?
The safety data advises against it—there isn't enough information to know whether it's safe for the baby. Talk with your doctor or pharmacist before taking it if you're pregnant, planning to become pregnant, or breastfeeding.
What is L-Theanine and where does it come from?
L-Theanine is an amino acid naturally found in tea leaves. It's thought to promote relaxation and support mental clarity, though researchers are still working out exactly how it affects the brain.
Does L-Theanine actually improve focus and thinking?
The evidence supports it as possibly effective for cognitive function, so there's some promise. For other brain-related concerns like Alzheimer's or age-related decline, the research we have isn't strong enough yet to say whether it works.
What side effects should I watch for?
Headaches, drowsiness, and changes to sleep (longer sleep or more vivid dreams) are the most commonly reported. One case of facial tics was reported but stopped once the supplement was discontinued. If you experience anything unusual, stop taking it and let your doctor know.
Is this safe to use long-term?
L-Theanine is generally well tolerated in the short term, but the long-term safety data just isn't there. If you're thinking of taking it regularly over months or years, chat with your pharmacist or doctor about monitoring your use.

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

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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

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 →
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 6 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.

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 →

Parts of this content are provided by the Therapeutic Research Center, LLC.

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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