Major interaction on record — check this product against your medications before combining. Check your meds →
Dietary supplement

HistaBlock Ingredients & Drug Interactions

by Nature's Sunshine

HistaBlock 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 HistaBlock 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

HistaBlock is a dietary supplement by Nature's Sunshine with 4 active ingredients. Its ingredients are commonly taken for inflammation and swelling, sinus and nasal congestion, digestion support.Based on those ingredients, 1,334 medications have a known interaction with it, the most serious rated major. The ingredients most likely to interact are Quercetin, Bitter Orange, Nettle. Use the checker below to test your specific medication, or read the full HelloPharmacist Interaction Report.

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Check Your Meds Against HistaBlock by Nature's Sunshine

Ask about any prescription or over-the-counter medication and we check it for interactions with HistaBlock by Nature's Sunshine — and tell you which ingredient is responsible.

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HelloPharmacist Scorecard of HistaBlock by Nature's Sunshine

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 6, 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 0 of its 4 active ingredients.
  • “Proprietary Blend” is a proprietary blend — the label gives one combined amount (540 mg) without saying how much of each component you get.

HistaBlock contains four active ingredients. Bromelain is an enzyme from pineapple that may help with inflammation.

Nettle (stinging nettle leaf) is an herb traditionally used for allergies and other conditions. Quercetin is a plant flavonoid (a type of antioxidant compound) found in many foods and plants.

Bitter orange is a citrus fruit extract. The product also contains inactive ingredients — dicalcium phosphate, cellulose, vegetable magnesium stearate, and silicon dioxide — which are binders and capsule materials.

Does it work?

Not established
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
Not established

The graded evidence we hold for these ingredients covers different conditions than the ones this product is marketed for, so there's no established rating for its stated use.

Why this rating?
  • The label markets this product for: support respiratory health and airways.
  • We looked for evidence on: Allergic rhinitis (hay fever), Asthma, Seasonal allergies, Nasal congestion.
  • The closest evidence on file: Quercetin is rated "Insufficient Reliable Evidence To Rate" for Allergic rhinitis (hay fever) (Natural Medicines).
  • Also on file: Quercetin is rated "Insufficient Reliable Evidence To Rate" for Asthma.
  • Also on file: Stinging Nettle is rated "Insufficient Reliable Evidence To Rate" for Allergic rhinitis (hay fever), Asthma.

The evidence for most of HistaBlock's ingredients is limited. Nettle is possibly effective for diabetes, though the data we hold rates other uses — including allergic rhinitis — as having insufficient evidence.

Quercetin's athletic performance use is rated possibly ineffective; its other indications lack reliable evidence in our data. Bromelain and bitter orange have insufficient evidence to rate for their listed uses.

None of the ingredients here has strong established proof for the role they may play in this formula.

The evidence, ingredient by ingredient Bromelain Stinging Nettle Quercetin Bitter Orange

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 4 of the 4 matched ingredients.
  • Pregnancy & breastfeeding safety ratings cover 4 of 4.
  • General safety write-ups exist for 4 of 4.
  • Remember: this measures how much safety information exists. Thin data is not the same as being safe.

Bromelain is generally well tolerated short-term, but long-term safety data are scarce. Common side effects include diarrhea, flatulence, and upset stomach.

Allergic reactions (IgE-mediated) can occur, especially if inhaled; if you're sensitive to pineapple, mention that to your pharmacist. Nettle is generally well tolerated for most adults when used as directed, though constipation or diarrhea may occur; fresh plant contact causes itching and rash.

Rare reports of liver injury exist. Quercetin at food and typical supplement doses is generally well tolerated; high-dose safety is unclear.

Bitter orange is the most cautious ingredient — at medicinal doses it may be unsafe, with reports of high blood pressure, rapid heart rate, heart attack, stroke, and irregular heartbeats, especially when combined with caffeine or other stimulants. During pregnancy, nettle is likely unsafe and bitter orange is possibly unsafe; bromelain and quercetin lack sufficient safety data.

During breastfeeding, all four ingredients either lack safety data or are advised against. Talk with your doctor or pharmacist before use if you are pregnant or nursing.

Side effects, ingredient by ingredient Bromelain Stinging Nettle Quercetin Bitter Orange

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?
  • 4 of the 4 matched ingredients can interact with medications — Quercetin, Stinging Nettle, Bromelain, Bitter Orange.
  • 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.
  • For scale: 1,335 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 HistaBlock, check with your doctor or pharmacist if you take monoamine oxidase inhibitors (MAOIs), sedatives like midazolam, or heart drugs that prolong the QT interval — these carry serious risks with bitter orange. Also double-check if you're on blood thinners (warfarin or others), antidiabetes drugs, stimulants, caffeine in medicinal amounts, certain antibiotics (quinolone or tetracycline), cholesterol drugs like pravastatin, diuretics, or lithium — all have documented interactions with one or more ingredients here.

Check your own medication Run your meds through the checker above

The bottom line

Scorecard at a glanceFormula with limited ingredient disclosure with no established evidence rating for its marketed use. Major medication interactions have been identified, and safety information is well characterized.

HistaBlock combines herbs and plant extracts whose effectiveness for their listed uses isn't well established in our data. More importantly, it carries multiple medication interactions — some serious — that you need to check carefully.

If you take any prescription drugs, especially antidepressants, blood thinners, heart medications, sedatives, diabetes drugs, or stimulants, run them through the interaction checker below or discuss this product with your doctor or pharmacist before starting it.

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

Assessment coverage: 4 of 4 active ingredients matched to our full ingredient reviews (monographs). Based on the product label dated Oct 24, 2022.

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 HistaBlock, straight from the product label.

Brand Nature's Sunshine
Barcode (UPC) 099904007765
Net contents 90 Capsule(s)
Market status On market
Date entered into DSLD Oct 24, 2022
DSLD ID 278116
Product type Other Combinations
Supplement form Capsule
Dietary claims / uses 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 HistaBlock by Nature's Sunshine, 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:
2 Capsule(s)
Maximum serving Sizes:
2 Capsule(s)
Servings per container
45
UPC/BARCODE
099904007765
IngredientAmount% DV
Proprietary Blend540 mg--
Bromelain0 NP--
Nettle0 NP--
Quercetin0 NP--
Bitter Orange0 NP--

Other ingredients: Dicalcium Phosphate, Capsule, Cellulose, Vegetable Magnesium Stearate, Silicon Dioxide

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.
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.

General Statements

Bottle made from 100% post consumer recycled material. We are committed to you and our planet. Scan to learn more.

New look! Same great product

Formulation

Powerful antioxidants help support the health of the airway passages and mucous membrane.

Supports the respiratory system Supports healthy airways Supports mucous membranes

Formula

Stinging nettle, quercetin, bromelain and bitter orange offer natural help with seasonal irritants.

Precautions

Do not use if inner seal is missing or damaged.

FDA Statement of Identity

Dietary Supplement

Brand IP Statement(s)

Natures Sunshine Herbal experts since 1972

Suggested/Recommended/Usage/Directions

Recommended Use: Take 2 capsules twice daily.

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

See for yourself

HistaBlock by Nature's Sunshine label

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

HistaBlock 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 HistaBlock by Nature's Sunshine

These are the 4 active ingredients this product is made of. Select any to open its full monograph.

Serving size2 Capsule(s) Dosage formCapsule Servings per container45 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

540 mg per serving

Other (inactive) ingredients: Dicalcium Phosphate, Capsule, Cellulose, Vegetable Magnesium Stearate, Silicon Dioxide. These complete the product’s ingredient list but are not active constituents.

Interaction report

HistaBlock by Nature's Sunshine Drug Interactions

Want to check YOUR meds against HistaBlock?

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
1,334Drugs
10 Major 1,320 Moderate 4 Minor

Ingredients driving the most interactions

Quercetin 1,169
Bitter Orange 957
Nettle 164
Bromelain 141

Individual Drug Interactions

The ingredients in HistaBlock interact with 1,334 drugs. Click any drug to see the details.

4 of the 4 ingredients in HistaBlock interact with drugs. Each result below shows which ingredient is responsible. Quercetin Bitter Orange Nettle Bromelain

Each ingredient & the kinds of drugs it affects

For each ingredient in HistaBlock 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.

Quercetin21 drug types · 1,169 drugs

Antidiabetes Drugs

Theoretically, concomitant use of quercetin and antidiabetes drugs might increase the risk of hypoglycemia.

Clinical research suggests that a combination of quercetin, myricetin, and chlorogenic acid reduce levels of fasting glucose in patients with type 2 diabetes, including those already taking antidiabetes agents. The effect of quercetin alone is unknown.

Likelihood Possible Evidence B
Antihypertensive Drugs

Theoretically, taking quercetin with antihypertensive drugs might increase the risk of hypotension.

Quercetin can modestly decrease blood pressure in people with mild hypertension. Theoretically, it might have additive blood pressure lowering effects when used with antihypertensive drugs.

Likelihood Possible Evidence B
Cyclosporine (Neoral, Sandimmune)

Theoretically, concomitant use might increase the levels and adverse effects of cyclosporine.

A small study in healthy volunteers shows that pretreatment with quercetin increases plasma levels and prolongs the half-life of a single dose of cyclosporine, possibly due to inhibition of p-glycoprotein or cytochrome P450 3A4 (CYP3A4), which metabolizes cyclosporin.

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

Theoretically, concomitant use might increase the levels and adverse effects of CYP2C8 substrates.

In vitro research shows that quercetin inhibits CYP2C8. Inhibition of paclitaxel (Taxol) metabolism via CYP2C8 has been reported in vitro. However, a small study in humans found no effect of quercetin on rosiglitazone (Avandia), which is also a CYP2C8 substrate.

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

Theoretically, concomitant use might increase the levels and adverse effects of CYP2C9 substrates.

A small clinical study in healthy volunteers shows that taking quercetin 500 mg twice daily for 10 days prior to taking diclofenac, a CYP2C9 substrate, increases diclofenac plasma levels by 75% and prolongs the half-life by 32.5%. Animal research also shows that pretreatment with quercetin increases plasma levels and prolongs the half-life of losartan (Cozaar), a substrate of CYP2C9. Furthermore, laboratory research shows that quercetin inhibits CYP2C9.

Likelihood Possible Evidence B
Cytochrome P450 2D6 (Cyp2D6) Substrates

Theoretically, concomitant use might increase the levels and adverse effects of CYP2D6 substrates.

In vitro research show that quercetin inhibits CYP2D6. This effect has not been reported in humans.

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

Theoretically, concomitant use might alter the effects and adverse effects of CYP3A4 substrates.
A small clinical study in healthy volunteers shows that pretreatment with quercetin increases plasma levels and prolongs the half-life of a single dose of cyclosporine (Neoral, Sandimmune), a substrate of CYP3A4. Animal research also shows that pretreatment with quercetin increases plasma levels and prolongs the half-life of losartan (Cozaar) and quetiapine (Seroquel), substrates of CYP3A4. Other laboratory research also shows that quercetin inhibits CYP3A4. However, one clinical study shows that quercetin can increase the metabolism of midazolam, a substrate of CYP3A4, and decrease serum concentrations of midazolam by about 24% in some healthy individuals, suggesting possible induction of CYP3A4.

Likelihood Possible Evidence D
Diclofenac (Voltaren, Others)

Theoretically, concomitant use might increase the levels and adverse effects of diclofenac.

A small clinical study in healthy volunteers shows that taking quercetin 500 mg twice daily for 10 days prior to taking diclofenac increases diclofenac plasma levels by 75% and prolongs the half-life by 32.5%. This is thought to be due to inhibition of CYP2C9 by quercetin.

Likelihood Probable Evidence B
Losartan (Cozaar)

Theoretically, concomitant use might increase the effects and adverse effects of losartan and decrease the effects of its active metabolite.

Animal research shows that pretreatment with quercetin increases plasma levels and prolongs the half-life of losartan (Cozaar) while decreasing plasma levels of losartan's active metabolite. This metabolite, which is around 10-fold more potent than losartan, is the result of cytochrome P450 (CYP) 2C9- and CYP3A4-mediated transformation of losartan. Additionally, in vitro research shows that quercetin may inhibit P-glycoprotein-mediated efflux of losartan from the intestines, resulting in increased absorption of losartan. These results suggest that concomitant use of quercetin and losartan might increase systemic exposure to losartan while also decreasing plasma concentrations of losartan's active and more potent metabolite.

Likelihood Possible Evidence D
Midazolam (Versed)

Theoretically, concomitant use might decrease the levels and effects of midazolam.

A small clinical study in healthy volunteers shows that quercetin can increase the metabolism of midazolam, with a decrease in AUC of about 24%.

Likelihood Possible Evidence B
Mitoxantrone

Theoretically, quercetin might increase the effects and adverse effects of mitoxantrone.
In vitro research shows that quercetin increases the intracellular accumulation and cytotoxicity of mitoxantrone, possibly through inhibition of breast cancer resistance protein (BCRP), of which mitoxantrone is a substrate. So far, this interaction has not been reported in humans.

Likelihood Possible Evidence D
Organic Anion Transporter 1 (Oat1) Substrates

Theoretically, concomitant use might increase the effects and adverse effects of OAT1 substrates.

In vitro research shows that quercetin is a strong non-competitive inhibitor of OAT1, with half-maximal inhibitory concentration (IC50) values less than 10 mcM. So far, this interaction has not been reported in humans.

Likelihood Possible Evidence D
Organic Anion Transporter 3 (Oat3) Substrates

Theoretically, concomitant use might increase the effects and adverse effects of OAT3 substrates.

In vitro research shows that quercetin is a strong non-competitive inhibitor of OAT3, with half-maximal inhibitory concentration (IC50) values as low as 0.75 mcM. So far, this interaction has not been reported in humans.

Likelihood Possible Evidence D
Organic Anion-Transporting Polypeptide Substrates (Oatp)

Theoretically, concomitant use might increase the effects and adverse effects of OATP substrates.

In vitro evidence shows that quercetin can inhibit organic anion-transporting peptide (OATP) 1B1-mediated uptake of estrone-3-sulfate and pravastatin. Furthermore, clinical research in healthy males shows that intake of quercetin along with pravastatin increases the AUC of pravastatin by 24%, prolongs its half-life by 14%, and decreases its apparent clearance by 18%, suggesting that quercetin modestly inhibits the uptake of pravastatin in hepatic cells.

Likelihood Possible Evidence B
P-Glycoprotein Substrates

Theoretically, concomitant use might alter the effects and adverse effects of P-glycoprotein substrates.

There is preliminary evidence that quercetin inhibits the gastrointestinal P-glycoprotein efflux pump, which might increase the bioavailability and serum levels of drugs transported by the pump. A small study in healthy volunteers reported that pretreatment with quercetin increased bioavailability and plasma levels after a single dose of cyclosporine (Neoral, Sandimmune). Also, two small studies have shown that quercetin might decrease the absorption of talinolol, a substrate transported by the gastrointestinal P-glycoprotein efflux pump. However, in another small study, several days of quercetin treatment did not significantly affect the pharmacokinetics of saquinavir (Invirase). The reason for these discrepancies is not entirely clear. Until more is known, use quercetin cautiously in combination with P-glycoprotein substrates.

Likelihood Possible Evidence B
Pravastatin (Pravachol)

Theoretically, concomitant use might increase the effects and adverse effects of pravastatin.
In vitro evidence shows that quercetin can inhibit OATP 1B1-mediated uptake of pravastatin. Also, preliminary clinical research in healthy males shows that intake of quercetin along with pravastatin increases the maximum concentration of pravastatin by 24%, prolongs its half-life by 14%, and decreases its apparent clearance by 18%, suggesting that quercetin modestly inhibits the uptake of pravastatin in hepatic cells.

Likelihood Possible Evidence B
Prazosin (Minipress)

Theoretically, quercetin might increase the effects and adverse effects of prazosin.
In vitro research shows that quercetin inhibits the transcellular efflux of prazosin, possibly through inhibition of breast cancer resistance protein (BCRP), of which prazosin is a substrate. BCRP is an ATP-binding cassette efflux transporter in the intestines, kidneys, and liver. So far, this interaction has not been reported in humans.

Likelihood Possible Evidence D
Quetiapine (Seroquel)

Theoretically, concomitant use might increase the effects and adverse effects of quetiapine.
Animal research shows that pretreatment with quercetin can increase plasma levels of quetiapine and prolong its clearance, possibly due to inhibition of cytochrome P450 3A4 (CYP3A4) by quercetin. Additionally, the brain-to-plasma ratio of quetiapine concentrations increased, possibly due to inhibition of P-glycoprotein at the blood-brain barrier. This interaction has not been reported in humans.

Likelihood Possible Evidence D
Quinolone Antibiotics

Theoretically, concomitant use might inhibit the effects of quinolone antibiotics.
In vitro, quercetin binds to the DNA gyrase site on bacteria, which may interfere with the activity of quinolone antibiotics.

Likelihood Possible Evidence B
Sulfasalazine (Azulfidine)

Theoretically, quercetin might increase the effects and adverse effects of sulfasalazine.
Animal research shows that quercetin increases the maximum serum concentration (Cmax) and area under the curve (AUC) of sulfasalazine, possibly through inhibition of breast cancer resistance protein (BCRP), of which sulfasalazine is a substrate. So far, this interaction has not been reported in humans.

Likelihood Possible Evidence D
Warfarin (Coumadin)

Theoretically, quercetin may increase the risk of bleeding if used with warfarin.
Animal and in vitro studies show that quercetin might increase serum levels of warfarin. Quercetin and warfarin have the same human serum albumin (HSA) binding site, and in vitro research shows that quercetin has stronger affinity for the HSA binding site and can theoretically displace warfarin, causing higher serum levels of warfarin. Animal research shows that taking quercetin for 2 weeks before initiating warfarin increases the maximum serum level of warfarin by 30%, the half-life by 10%, and the overall exposure by 63% when compared with control. Concomitant administration of quercetin and warfarin, without quercetin pre-treatment, also increased these measures, but to a lesser degree. Researchers theorize that inhibition of CYP3A4 by quercetin may explain these effects. So far, this interaction has not been reported in humans.

Likelihood Possible Evidence D
Quercetin full monograph & interactions

Bitter Orange13 drug types · 957 drugs

Midazolam (Versed)

Bitter orange might increase blood levels of midazolam.
One small clinical study shows that bitter orange juice can increase midazolam levels, likely through inhibition of cytochrome P450 3A4 (CYP3A4). Theoretically, bitter orange might increase the risk of midazolam-related adverse effects.

Likelihood Probable Evidence B
Monoamine Oxidase Inhibitors (Maois)

Theoretically, taking MAOIs with synephrine-containing bitter orange preparations might increase the hypertensive effects of synephrine, potentially leading to hypertensive crisis.
Bitter orange contains tyramine, octopamine, and synephrine, which are MAO substrates.

Likelihood Probable Evidence D
Antidiabetes Drugs

Theoretically, bitter orange might increase the risk of hypoglycemia when taken with antidiabetes drugs.
Some clinical research shows that drinking a tea containing bitter orange and Indian snakeroot reduces fasting and postprandial glucose levels in patients with type 2 diabetes who are using antidiabetes drugs. However, it is unclear if these effects are due to bitter orange, Indian snakeroot, or the combination. An animal study also shows that p-synephrine in combination with gliclazide , a sulfonylurea, causes an additional 20% to 44% decrease in glucose levels when compared with gliclazide alone.

Likelihood Possible Evidence B
Caffeine

Bitter orange might increase blood pressure and heart rate when taken with caffeine.
Small clinical studies show that taking bitter orange in combination with caffeine can increase blood pressure and heart rate in otherwise healthy normotensive adults. Theoretically, this might increase the risk of serious cardiovascular adverse effects.

Likelihood Possible Evidence B
Colchicine

Bitter orange might affect colchicine levels.
Colchicine is a substrate of P-glycoprotein and cytochrome P450 3A4 (CYP3A4). Bitter orange has been reported to inhibit CYP3A4 and increase levels of CYP3A4 substrates. However, one small clinical study in healthy adults shows that drinking bitter orange juice 240 mL twice daily for 4 days and taking a single dose of colchicine 0.6 mg on the 4th day decreases colchicine peak serum levels by 24%, time to peak serum level by 1 hour, and overall exposure to colchicine by 20%. The clinical significance of this finding is unclear.

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

Bitter orange might increase levels of drugs metabolized by CYP3A4.
Small clinical studies suggest that single or multiple doses of freshly squeezed bitter orange juice 200-240 mL can inhibit CYP3A4 metabolism of drugs, causing increased drug levels and potentially increasing the risk of adverse effects. However, the extent of the effect of bitter orange on CYP3A4-mediated drug interactions is unknown. Some evidence suggests that bitter orange selectively inhibits intestinal CYP3A4, but not hepatic CYP3A4. Its effect on P-glycoprotein, which strongly overlaps with CYP3A4 interactions, is unclear. One small clinical study shows that drinking 8 ounces of freshly squeezed bitter orange juice has no effect on cyclosporine, which seems to be more dependent on hepatic CYP3A4 and P-glycoprotein than intestinal CYP3A4.

Likelihood Possible Evidence B
Dextromethorphan (Robitussin Dm, Others)

Bitter orange might increase blood levels of dextromethorphan.
One small clinical study shows that bitter orange juice increases dextromethorphan levels, likely through cytochrome P450 3A4 (CYP3A4) inhibition. Theoretically, bitter orange might increase the risk for dextromethorphan-related adverse effects.

Likelihood Possible Evidence B
Felodipine (Plendil)

Bitter orange might increase blood levels of felodipine.
One small clinical study shows that bitter orange juice increases felodipine levels, likely through cytochrome P450 3A4 (CYP3A4) inhibition. Theoretically, bitter orange might increase the risk for felodipine-related adverse effects.

Likelihood Probable Evidence B
Indinavir (Crixivan)

Bitter orange might increase blood levels of indinavir.
One small clinical study shows that bitter orange juice slightly increases indinavir levels, but this effect is likely to be clinically insignificant. Bitter orange selectively inhibits intestinal cytochrome P450 3A4 (CYP3A4); however, the metabolism of indinavir seems to be more dependent on hepatic CYP3A4. The effect of bitter orange on other protease inhibitors has not been studied.

Likelihood Possible Evidence B
Qt Interval-Prolonging Drugs

Theoretically, bitter orange might have an additive effect when combined with drugs that prolong the QT interval, potentially increasing the risk of ventricular arrhythmias.
One case report suggests that taking bitter orange in combination with other stimulants such as caffeine might prolong the QT interval in some patients.

Likelihood Possible Evidence D
Sildenafil (Viagra)

Bitter orange juice might increase blood levels of sildenafil.
A small clinical study in healthy adult males shows that drinking freshly squeezed bitter orange juice 250 mL daily for 3 days and taking a single dose of sildenafil 50 mg on the 3rd day increases the peak plasma concentration of sildenafil by 18% and the overall exposure to sildenafil by 44%. Theoretically, this may be due to inhibition of cytochrome P450 3A4 by bitter orange.

Likelihood Probable Evidence B
Stimulant Drugs

Theoretically, bitter orange might increase the risk of hypertension and adverse cardiovascular effects when taken with stimulant drugs.
Bitter orange appears to have stimulant effects.

Likelihood Possible Evidence B
Cytochrome P450 2D6 (Cyp2D6) Substrates

Theoretically, bitter orange might increase levels of drug metabolized by CYP2D6.
In vitro research shows that octopamine, a constituent of bitter orange, weakly inhibits CYP2D6 enzymes. This effect has not been reported in humans.

Likelihood Possible Evidence D
Bitter Orange full monograph & interactions

Nettle4 drug types · 164 drugs

Antidiabetes Drugs

Theoretically, stinging nettle might have additive effects with antidiabetes drugs.
Clinical research shows that stinging nettle might decrease blood glucose levels in patients with diabetes.

Likelihood Possible Evidence B
Diuretic Drugs

Theoretically, combining stinging nettle with diuretic drugs may have additive effects.
Animal research suggests that the above ground parts and roots of stinging nettle may have a diuretic effect.

Likelihood Possible Evidence D
Lithium

Theoretically, stinging nettle might reduce excretion and increase levels of lithium.
Animal research suggests that stinging nettle has diuretic and natriuretic properties, which could alter the excretion of lithium. The dose of lithium might need to be decreased.

Likelihood Possible Evidence D
Warfarin (Coumadin)

There is some concern that stinging nettle might decrease the effects of anticoagulant drugs such as warfarin.
Stinging nettle contains a significant amount of vitamin K. When taken in large quantities, this might interfere with the activity of warfarin.

Likelihood Possible Evidence D
Nettle full monograph & interactions

Bromelain2 drug types · 141 drugs

Anticoagulant/Antiplatelet Drugs

Bromelain may have antiplatelet effects and may increase the risk of bleeding if used with anticoagulant or antiplatelet drugs.
There is one case report of a patient experiencing minor bruising while taking bromelain with naproxen. Bromelain is thought to have antiplatelet activity. Whether this interaction is of concern with topical bromelain is unclear. Interference with coagulation of burn wounds has been reported in a patient receiving bromelain-based enzymatic debridement. However, observational research has found that topical bromelain debridement is not associated with increases or decreases in laboratory markers of coagulation when compared with surgical debridement.

Likelihood Possible Evidence D
Tetracycline Antibiotics

Theoretically, bromelain might increase levels of tetracycline antibiotics.
Laboratory research suggests that bromelain might increase the absorption of tetracycline antibiotics. However, a study in healthy adults reported no difference in tetracycline plasma levels when a 500 mg dose was taken with or without bromelain 80 mg.

Likelihood Possible Evidence B
Bromelain full monograph & interactions
The maker

Brand information

Manufacturer and brand details for HistaBlock, from the product label.

Nature's Sunshine

See all Nature's Sunshine products
Name
Nature's Sunshine Products, Inc.
City
Spanish Fork
State
Utah
ZipCode
84660
Phone Number
1-800-223-8225
Web Address
www.naturessunshine.com
Pharmacist Counseling Corner

HistaBlock by Nature's Sunshine: Common Questions

Does HistaBlock by Nature's Sunshine interact with any medications?
Yes. Based on its ingredients, HistaBlock has a known interaction with 1,334 medications, including 10 rated major. Use the checker to see how it interacts with a specific drug.
How can one product interact with so many drugs?
HistaBlock contains 4 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.
Will HistaBlock help with my allergies?
Nettle is possibly effective for diabetes, but for allergic rhinitis (hay fever) — the main allergy use listed — we don't have reliable evidence that it works. The other three ingredients also lack established proof for allergy relief in our data. Talk with your doctor about whether this product is right for your allergies.
What are the most common side effects?
From bromelain, you might experience diarrhea, flatulence, or upset stomach. Nettle may cause constipation or diarrhea. Quercetin can cause headache or tingling in the hands and feet. Bitter orange — especially at higher doses — raises blood pressure and heart rate, and is the ingredient with the most cautionary adverse effects on file.
Can I take this if I'm pregnant or breastfeeding?
No, not safely based on the data we hold. Nettle is likely unsafe in pregnancy, and bitter orange is possibly unsafe. Bromelain and quercetin lack enough safety information — meaning we can't say it's safe either way. Talk with your doctor or pharmacist about your specific situation before taking any supplement during pregnancy or while nursing.
What is bromelain, and does it have side effects?
Bromelain is an enzyme from pineapple that may help with inflammation. It's generally well tolerated when taken by mouth, but can cause diarrhea, gas, and stomach upset. If you're allergic to pineapple, mention that — allergic reactions to bromelain are possible, especially if inhaled.
Why does bitter orange have a 'Major' warning with some medications?
Bitter orange contains compounds (synephrine, octopamine, and tyramine) that can dramatically raise blood pressure, especially when combined with certain older antidepressants (MAOIs) or sedatives. It also blocks how your liver breaks down some drugs, causing them to build up to dangerous levels. That's why it's critical to check it with your medications before taking it.
Is HistaBlock safe to take long-term?
Long-term safety data for these ingredients — particularly bromelain and bitter orange — are limited or unknown. The evidence we hold advises caution with long-term use. If you're considering taking it regularly, discuss the duration and your personal health picture with your doctor or pharmacist.

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.

HistaBlock label
Go deeper

The Full Monographs Behind HistaBlock’s Ingredients

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

Herb & supplement monograph

Bromelain

Interacts with 141 drugs

Bromelain is a group of protein-digesting enzymes from pineapple that people take mainly for inflammation, swelling, and sinus problems. Some early studies are promising, but the overall evi...

Read the full Bromelain monograph → Herb & supplement monograph

Stinging Nettle

Interacts with 164 drugs

Stinging nettle is a common plant used as food and in traditional medicine, most often for prostate symptoms, allergies, and joint pain. The evidence is mixed and mostly preliminary, so it i...

Read the full Stinging Nettle monograph → Herb & supplement monograph

Quercetin

Interacts with 1,169 drugs

Quercetin is a plant flavonoid with antioxidant and anti-inflammatory properties found in many common foods and sold as a supplement. While early research is interesting for allergies, blood...

Read the full Quercetin monograph → Herb & supplement monograph

Bitter Orange

Interacts with 957 drugs

Bitter orange is a citrus fruit whose extracts contain synephrine, a mild stimulant often added to weight-loss and energy supplements. Evidence that it works for weight loss or performance i...

Read the full Bitter Orange monograph →
Sources

Sources & How We Checked

HistaBlock'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 115 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.

Bromelain 19 references
  1. Nettis E, Napoli G, Ferrannini A, Tursi A. IgE-mediated allergy to bromelain. Allergy 2001;56:257-8. PubMed
  2. Taussig SJ, Batkin S. Bromelain, the enzyme complex of pineapple (Ananas comosus) and its clinical application. An update. J Ethnopharmacol 1988;22:191-203.. PubMed
  3. Bradbrook ID, Morrison PJ, Rogers HJ. The effect of bromelain on the absorption of orally administered tetracycline. Br J Clin Pharmacol 1978;6:552-4. PubMed
  4. Bush TM, Rayburn KS, Holloway SW, et al. Adverse interactions between herbal and dietary substances and prescription medications: a clinical survey. Altern Ther Health Med 2007;13:30-5.
  5. Brien S, Lewith G, Walker AF, et al. Bromelain as an adjunctive treatment for moderate-to-severe osteoarthritis of the knee: a randomized placebo-controlled pilot study. QJM 2006;99:841-50. PubMed
  6. Mori S, Ojima Y, Hirose T, et al. The clinical effect of proteolytic enzyme containing bromelain and trypsin on urinary tract infection evaluated by double blind method. Acta Obstet Gynaecol Jpn 1972;19:147-53.
  7. Glaser D, Hilberg T. The influence of bromelain on platelet count and platelet activity in vitro. Platelets 2006;17:37-41. PubMed
  8. Heinicke R M, van der Wal L, Yokoyama M. Effect of bromelain (Ananase) on human platelet aggregation. Experientia 1972;28:844-5. PubMed
  9. Gailhofer, G., Wilders-Truschnig, M., Smolle, J., and Ludvan, M. Asthma caused by bromelain: an occupational allergy. Clin Allergy 1988;18(5):445-450. PubMed
  10. Mattei, O., Fabri, G., and Farina, G. [Occupational health experience regarding four cases of asthma due to bromelain (author's transl)]. Medicina del Lavoro 1979;70(5):404-409.
  11. Galleguillos, F. and Rodriguez, J. C. Asthma caused by bromelin inhalation. Clin Allergy 1978;8(1):21-24. PubMed
  12. Perez-Camo I, Quirce S, Duran MA, and et al. Latex allergy: evidence of cross-reactivity with papain and bromelain [abstract]. Allergy 1996;51(suppl 31):48.
  13. Martin GJ, Ehrenreich J, and Asbell N. Bromelain: pineapple proteases with anti-edema activity. Exp Med Surg 1962;20:227-247.
  14. Kasemsuk T, Saengpetch N, Sibmooh N, Unchern S. Improved WOMAC score following 16-week treatment with bromelain for knee osteoarthritis. Clin Rheumatol. 2016 Oct;35(10):2531-40. PubMed
  15. Kutlu Ö, DemirbaS A, Elmas ÖF, Güvenç U, Metin A. Fixed drug eruption: a new side effect of bromelain. Contact Dermatitis 2020. Online ahead of print. PubMed
  16. Shoham Y, Shapira E, Haik J, et al. Bromelain-based enzymatic debridement of chronic wounds: Results of a multicentre randomized controlled trial. Wound Repair Regen 2021;29(6):899-907. PubMed
  17. Pfister P, Garcia Wendel PD, Kim BS, et al. Coagulation side effects of enzymatic debridement in burned patients. Burns 2022. PubMed
  18. Hasham S, Riyat H, Fletcher A, O'Boyle CP, Alexander S. To bleed or not to bleed? Case series and discussion of haemorrhage risk with enzymatic debridement in burn injuries. Scars Burn Heal 2023;9:20595131231168333. PubMed
  19. Leelakanok N, Petchsomrit A, Janurai T, Saechan C, Sunsandee N. Efficacy and safety of bromelain: A systematic review and meta-analysis. Nutr Health 2023. PubMed

See these in context on the Bromelain monograph →

Stinging Nettle 23 references
  1. Monographs on the medicinal uses of plant drugs. Exeter, UK: European Scientific Co-op Phytother, 1997.
  2. Newall CA, Anderson LA, Philpson JD. Herbal Medicine: A Guide for Healthcare Professionals. London, UK: The Pharmaceutical Press, 1996.
  3. The Review of Natural Products by Facts and Comparisons. St. Louis, MO: Wolters Kluwer Co., 1999.
  4. Schulz V, Hansel R, Tyler VE. Rational Phytotherapy: A Physician's Guide to Herbal Medicine. Terry C. Telger, transl. 3rd ed. Berlin, GER: Springer, 1998.
  5. Leung AY, Foster S. Encyclopedia of Common Natural Ingredients Used in Food, Drugs and Cosmetics. 2nd ed. New York, NY: John Wiley & Sons, 1996.
  6. Brinker F. Herb Contraindications and Drug Interactions. 2nd ed. Sandy, OR: Eclectic Medical Publications, 1998.
  7. Mittman P. Randomized, double-blind study of freeze-dried Urtica dioica in the treatment of allergic rhinitis. Planta Med 1990;56:44-7.
  8. Vontobel HP, Herzog R, Rutishauser G, Kres H. [Results of a double-blind study on the effectiveness of ERU (extractum radicis Urticae) capsules in conservative treatment of benign prostatic hyperplasia]. (Abstract). Urologe A 1985;24:49-51.
  9. Randall C, Randall H, Dobbs F, et al. Randomized controlled trial of nettle sting for treatment of base-of-thumb pain. J R Soc Med 2000;93:305-9. PubMed
  10. Caliskaner Z, Karaayvaz M, Ozturk S. Misuse of a herb: stinging nettle (Urtica urens) induced severe tongue oedema. Complement Ther Med 2004;12:57-8. PubMed
  11. Krzeski, T., Kazon, M., Borkowski, A., Witeska, A., and Kuczera, J. Combined extracts of Urtica dioica and Pygeum africanum in the treatment of benign prostatic hyperplasia: double-blind comparison of two doses. Clin Ther 1993;15(6):1011-1020.
  12. Randall, C., Meethan, K., Randall, H., and Dobbs, F. Nettle sting of Urtica dioica for joint pain--an exploratory study of this complementary therapy. Complement Ther Med 1999;7(3):126-131. PubMed
  13. Tahri, A., Yamani, S., Legssyer, A., Aziz, M., Mekhfi, H., Bnouham, M., and Ziyyat, A. Acute diuretic, natriuretic and hypotensive effects of a continuous perfusion of aqueous extract of Urtica dioica in the rat. J Ethnopharmacol 2000;73(1-2):95-100. PubMed
  14. Sahin, M., Yilmaz, H., Gursoy, A., Demirel, A. N., Tutuncu, N. B., and Guvener, N. D. Gynaecomastia in a man and hyperoestrogenism in a woman due to ingestion of nettle (Urtica dioica). N.Z.Med.J. 2007;120(1265):U2803.
  15. Randall, C., Dickens, A., White, A., Sanders, H., Fox, M., and Campbell, J. Nettle sting for chronic knee pain: a randomised controlled pilot study. Complement Ther.Med. 2008;16(2):66-72. PubMed
  16. Rayburn, K., Fleischbein, E., Song, J., Allen, B., Kundert, M., Leiter, C., and Bush, T. Stinging nettle cream for osteoarthritis. Altern.Ther.Health Med. 2009;15(4):60-61.
  17. Oliver, F., Amon, E. U., Breathnach, A., Francis, D. M., Sarathchandra, P., Black, A. K., and Greaves, M. W. Contact urticaria due to the common stinging nettle (Urtica dioica)-- histological, ultrastructural and pharmacological studies. Clin Exp Dermato PubMed
  18. Kulze, A. and Greaves, M. Contact urticaria caused by stinging nettles. Br.J Dermatol. 1988;119(2):269-270. PubMed
  19. Patten G. Medicinal plant review: Urtica. Aust J Med Herbalism 1993;5(1):5-13.
  20. Maor D, Little M. Skin contact with a stinging tree requiring intensive care unit admission. Contact Dermatitis. 2017 Nov;77(5):335-37. PubMed
  21. Easton L, Vaid S, Nagel AK, Venci JV, Fortuna RJ. Stinging Nettle (Urtica dioica): An Unusual Case of Galactorrhea. Am J Case Rep 2021;22:e933999. PubMed
  22. Niazi B, Ahmed K, Ahmed M, Ali S, Song K, Elias S. Drug-Induced Liver Injury from Herbal Liver Detoxification Tea. Case Rep Gastroenterol 2022;16(3):612-617. PubMed
  23. Nnamani I, Tolu-Akinnawo O, Dufera RR, Akintunde A, Maliakkal B. Tinospora cordifolia (Guduchi/Giloy)-Induced Liver Injury: A Case Review. Cureus 2023;15(5):e39793. PubMed

See these in context on the Stinging Nettle monograph →

Quercetin 26 references
  1. Shoskes DA, Zeitlin SI, Shahed A, Rajfer J. Quercetin in men with category III chronic prostatitis: A preliminary prospective, double-blind, placebo-controlled trial. Urol 1999;54:960-3. PubMed
  2. Starvic B. Quercetin in our diet: from potent mutagen to probable anticarcinogen. Clin Biochem 1994;27:245-8. PubMed
  3. Ferry DR, Smith A, Malkhandi J, et al. Phase I clinical trial of the flavonoid quercetin: Pharmacokinetics and evidence for in vivo tyrosine kinase inhibition. Clin Cancer Res 1996;2:659-67..
  4. Obach RS. Inhibition of human cytochrome P450 enzymes by constituents of St. John's wort, an herbal preparation used in the treatment of depression. J Pharmacol Exp Ther 2000;294:88-95. DOI
  5. Edwards RL, Lyon T, Litwin SE, et al. Quercetin reduces blood pressure in hypertensive subjects. J Nutr 2007;137:2405-11.
  6. Kim KA, Park PW, Kim HK, et al. Effect of quercetin on the pharmacokinetics of rosiglitazone, a CYP2C8 substrate, in healthy subjects. J Clin Pharmacol 2005;45:941-6. PubMed
  7. DiCenzo R, Frerichs V, Larppanichpoonphol P, et al. Effect of quercetin on the plasma and intracellular concentrations of saquinavir in healthy adults. Pharmacotherapy 2006;26:1255-61. PubMed
  8. Choi JS, Choi BC, Choi KE. Effect of quercetin on the pharmacokinetics of oral cyclosporine. Am J Health Syst Pharm 2004;61:2406-9. PubMed
  9. Choi JS, Jo BW, Kim YC. Enhanced paclitaxel bioavailability after oral administration of paclitaxel or prodrug to rats pretreated with quercetin. Eur J Pharm Biopharm 2004;57:313-8. PubMed
  10. Vaclavikova R, Horsky S, Simek P, Gut I. Paclitaxel metabolism in rat and human liver microsomes is inhibited by phenolic antioxidants. Naunyn Schmiedebergs Arch Pharmacol 2003;368:200-9. PubMed
  11. Di Bari L, Ripoli S, Pradhan S, Salvadori P. Interactions between quercetin and warfarin for albumin binding: A new eye on food/drug interference. Chirality 2010;22:593-6. PubMed
  12. Lamson, D. W. and Brignall, M. S. Antioxidants and cancer, part 3: quercetin. Altern.Med.Rev. 2000;5(3):196-208.
  13. Duan KM, Wang SY, Ouyang W, Mao YM, Yang LJ. Effect of quercetin on CYP3A activity in Chinese healthy participants. J Clin Pharmacol 2012;52(6):940-6. PubMed
  14. Wang SY, Duan KM, Li Y, et al. Effect of quercetin on P-glycoprotein transport ability in Chinese healthy subjects. Eur J Clin Nutr 2013;67(4):390-4. PubMed
  15. Nguyen MA, Staubach P, Wolffram S, Langguth P. Effect of single-dose and short-term administration of quercetin on the pharmacokinetics of talinolol in humans - Implications for the evaluation of transporter-mediated flavonoid-drug interactions. Eur J Pha PubMed
  16. Wu LX, Guo CX, Chen WQ, et al. Inhibition of the organic anion-transporting polypeptide 1B1 by quercetin: an in vitro and in vivo assessment. Br J Clin Pharmacol 2012;73(5):750-7.
  17. Ahrens MJ, Thompson DL. Effect of emulin on blood glucose in type 2 diabetics. J Med Food. 2013;16(3):211-5. PubMed
  18. Larson A, Witman MA, Guo Y, et al. Acute, quercetin-induced reductions in blood pressure in hypertensive individuals are not secondary to lower plasma angiotensin-converting enzyme activity or endothelin-1: nitric oxide. Nutr Res. 2012;32(8):557-64. PubMed
  19. Bedada SK, Neerati P. Evaluation of the effect of quercetin treatment on CYP2C9 enzyme activity of diclofenac in healthy human volunteers. Phytother Res. 2018 Feb;32(2):305-311. doi: 10.1002/ptr.5978. PubMed
  20. Zhao Q, Wei J, Zhang H. Effects of quercetin on the pharmacokinetics of losartan and its metabolite EXP3174 in rats. Xenobiotica 2019;49(5):563-8. PubMed
  21. Bhutani P, Rajanna PK, Paul AT. Impact of quercetin on pharmacokinetics of quetiapine: insights from in-vivo studies in wistar rats. Xenobiotica. 2020:1-7.
  22. Li C, Wang X, Bi Y, et al. Potent Inhibitors of Organic Anion Transporters 1 and 3 From Natural Compounds and Their Protective Effect on Aristolochic Acid Nephropathy. Toxicol Sci. 2020;175(2):279-291. PubMed
  23. Ni Y, Duan Z, Zhou D, et al. Identification of Structural Features for the Inhibition of OAT3-Mediated Uptake of Enalaprilat by Selected Drugs and Flavonoids. Front Pharmacol. 2020;11:802. PubMed
  24. Song YK, Yoon JH, Woo JK, et al. Quercetin is a flavonoid breast cancer resistance protein inhibitor with an impact on the oral pharmacokinetics of sulfasalazine in rats. Pharmaceutics 2020;12(5):397. PubMed
  25. Ahmad E, Jahangir M, Ismail MA, et al. Influence of quercetin pretreatment on pharmacokinetics of warfarin in rats. Curr Drug Saf 2022. PubMed
  26. Nambiar A, Kellogg D 3rd, Justice J, et al. Senolytics dasatinib and quercetin in idiopathic pulmonary fibrosis: results of a phase I, single-blind, single-center, randomized, placebo-controlled pilot trial on feasibility and tolerability. EBioMedicine 20 PubMed

See these in context on the Quercetin monograph →

Bitter Orange 47 references
  1. Penzak SR, Jann MW, Cold JA, et al. Seville (sour) orange juice: synephrine content and cardiovascular effects in normotensive adults. J Clin Pharmacol 2001;41:1059-63. PubMed
  2. Electronic Code of Federal Regulations. Title 21. Part 182 -- Substances Generally Recognized As Safe. Available at: https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?CFRPart=182
  3. Calapai G, Firenzuoli F, Saitta A, et al. Antiobesity and cardiovascular toxic effects of Citrus aurantium extracts in the rat: A preliminary report. Fitoterapia 1999;70:586-92. DOI
  4. Keogh AM, Baron DW. Sympathomimetic abuse and coronary artery spasm. Br Med J 1985;291:940.
  5. Malhotra S, Bailey DG, Paine MF, Watkins PB. Seville orange juice-felodipine interaction: comparison with dilute grapefruit juice and involvement of furocoumarins. Clin Pharmacol Ther 2001;69:14-23. PubMed
  6. Pellati F, Benvenuti S, Melegari M, Firenzuoli F. Determination of adrenergic agonists from extracts and herbal products of Citrus aurantium L. var. amara by LC. J Pharm Biomed Anal 2002;29:1113-9. . PubMed
  7. Colker CM, Kalman DS, Torina GC, et al. Effects of Citrus aurantium extract, caffeine, and St. John's wort on body fat loss, lipid levels, and mood states in overweight healthy adults. Curr Ther Res 1999;60:145-153. DOI
  8. Penzak SR, Acosta EP, Turner M, et al. Effect of Seville orange juice and grapefruit juice on indinavir pharmacokinetics. J Clin Pharmacol 2002;42:1165-70. PubMed
  9. Edwards DJ, Fitzsimmons ME, Schuetz EG, et al. 6',7'-Dihydroxybergamottin in grapefruit juice and Seville orange juice: effects on cyclosporine disposition, enterocyte CYP3A4, and P-glycoprotein. Clin Pharmacol Ther 1999;65:237-44. PubMed
  10. Di Marco MP, Edwards DJ, Wainer IW, Ducharme MP. The effect of grapefruit juice and seville orange juice on the pharmacokinetics of dextromethorphan: the role of gut CYP3A and P-glycoprotein. Life Sci 2002;71:1149-60. PubMed
  11. Visentin V, Morin N, Fontana E, et al. Dual action of octopamine on glucose transport into adipocytes: inhibition via beta3-adrenoceptor activation and stimulation via oxidation by amine oxidases. J Pharmacol Exp Ther 2001;299:96-104.
  12. Nykamp DL, Fackih MN, Compton AL. Possible association of acute lateral-wall myocardial infarction and bitter orange supplement. Ann Pharmacother 2004;38:812-6. PubMed
  13. Fugh-Berman A, Myers A. Citrus aurantium, an ingredient of dietary supplements marketed for weight loss: Current status of clinical and basic Research. Exp Biol Med 2004;229:698-704.
  14. Suzuki O, Matsumoto T, Oya M, Katsumata Y. Oxidation of synephrine by type A and type B monoamine oxidase. Experientia 1979;35:1283-4. PubMed
  15. Nasir JM, Durning SJ, Ferguson M, et al. Exercise-induced syncope associated with QT prolongation and ephedra-free Xenadrine. Mayo Clin Proc 2004;79:1059-62.. PubMed
  16. Firenzuoli F, Gori L, Galapai C. Adverse reaction to an adrenergic herbal extract (Citrus aurantium). Phytomedicine 2005;12:247-8. PubMed
  17. Bouchard NC, Howland MA, Greller HA, et al. Ischemic stroke associated with use of an ephedra-free dietary supplement containing synephrine. Mayo Clin Proc 2005;80:541-5. PubMed
  18. Haller CA, Benowitz NL, Jacob P 3rd. Hemodynamic effects of ephedra-free weight-loss supplements in humans. Am J Med 2005;118:998-1003.. PubMed
  19. Bui LT, Nguyen DT, Ambrose PJ. Blood pressure and heart rate effects following a single dose of bitter orange. Ann Pharmacother 2006;40:53-7. PubMed
  20. Min B, Cios D, Kluger J, White CM. Absence of QTc-interval-prolonging or hemodynamic effects of a single dose of bitter-orange extract in healthy subjects. Pharmacotherapy 2005;25:1719-24. PubMed
  21. Gange CA, Madias C, Felix-Getzik EM, et al. Variant angina associated with bitter orange in a dietary supplement. Mayo Clin Proc 2006;81:545-8. PubMed
  22. Jordan S, Murty M, Pilon K. Products containing bitter orange or synephrine: suspected cardiovascular adverse reactions. Canadian Adverse Reaction Newsletter 2004;14:3-4.
  23. Burke J, Seda G, Allen D, Knee TS. A case of severe exercise-induced rhabdomyolysis associated with a weight loss dietary supplement. Mil Med 2007;172:656-8. PubMed
  24. Gray, S. and Woolf, A. D. Citrus aurantium used for weight loss by an adolescent with anorexia nervosa. J Adolesc.Health 2005;37(5):414-415. PubMed
  25. Haller, C. A., Duan, M., Jacob, P., III, and Benowitz, N. Human pharmacology of a performance-enhancing dietary supplement under resting and exercise conditions. Br J Clin Pharmacol 2008;65(6):833-840. PubMed
  26. Thomas, J. E., Munir, J. A., McIntyre, P. Z., and Ferguson, M. A. STEMI in a 24-year-old man after use of a synephrine-containing dietary supplement: a case report and review of the literature. Tex.Heart Inst.J 2009;36(6):586-590.
  27. Campbell-Tofte, J. I., Molgaard, P., Josefsen, K., Abdallah, Z., Hansen, S. H., Cornett, C., Mu, H., Richter, E. A., Petersen, H. W., Norregaard, J. C., and Winther, K. Randomized and double-blinded pilot clinical study of the safety and anti-diabetic ef
  28. Seifert, J. G., Nelson, A., Devonish, J., Burke, E. R., and Stohs, S. J. Effect of acute administration of an herbal preparation on blood pressure and heart rate in humans. Int J Med Sci 2011;8(3):192-197. PubMed
  29. Stohs, S. J., Preuss, H. G., Keith, S. C., Keith, P. L., Miller, H., and Kaats, G. R. Effects of p-synephrine alone and in combination with selected bioflavonoids on resting metabolism, blood pressure, heart rate and self-reported mood changes. Int J Med
  30. Wason, S., DiGiacinto, J. L., and Davis, M. W. Effects of grapefruit and Seville orange juices on the pharmacokinetic properties of colchicine in healthy subjects. Clin Ther 2012;34(10):2161-2173. PubMed
  31. Kaats, G. R., Miller, H., Preuss, H. G., and Stohs, S. J. A 60day double-blind, placebo-controlled safety study involving Citrus aurantium (bitter orange) extract. Food Chem Toxicol. 2013;55:358-362.
  32. Calapai, G., Firenzuoli, F., Saitta, A., Squadrito, F. R., Arlotta, M., Costantino, G., and Inferrera, G. Antiobesity and cardiovascular toxic effects of Citrus aurantium extracts in the rat: a preliminary report. Fitoterapia 12-1-1999;70(6):586-592. DOI
  33. Colker, C., Kalman, D., and Torina, G. Effects of Citrus aurantium extract, caffeine, and St. John's Wort on body fat loss, lipid levels, and mood states in overweight healthy adults. Curr Ther Res 1999;60:145-153. DOI
  34. Shara M, Stohs SJ. Safety evaluation of Bitter orange extract (p-synephrine) in healthy volunteers. J.Amer.Coll.Nutr. 2011;30:358.
  35. Lynch B. Review of the safety of p-synephrine and caffeine. Intertek-Cantox Report, 2013;1-20.
  36. Smith TB, Staub BA, Natarajan GM, et al. Acute myocardial infarction associated with dietary supplements containing 1,3-dimethylamylamine and Citrus aurantium. Tex Heart Inst J 2014;41(1):70-2. PubMed
  37. Shara M, Stohs SJ, Mukattash TL. Cardiovascular safety of oral p-synephrine (bitter orange) in healthy subjects: a randomized placebo-controlled cross-over clinical trial. Phytother Res. 2016;30(5):842-7.
  38. Liu Y, Santillo MF. Cytochrome P450 2D6 and 3A4 enzyme inhibition by amine stimulants in dietary supplements. Drug Test Anal. 2016;8(3-4):307-10. PubMed
  39. Abdelkawy KS, Donia AM, Turner RB, Elbarbry F. Effects of Lemon and Seville Orange Juices on the Pharmacokinetic Properties of Sildenafil in Healthy Subjects. Drugs R D. 2016 Sep;16(3):271-278. PubMed
  40. Gutiérrez-Hellín J, Salinero JJ, Abían-Vicen J, Areces F, Lara B, Gallo C, et al. Acute consumption of p-synephrine does not enhance performance in sprint athletes.J. Appl Physiol Nutr Metab. 2016;41(1):63-9. doi: 10.1139/apnm-2015-0299.
  41. Jung YP, Earnest CP, Koozehchian M, et al. Effects of ingesting a pre-workout dietary supplement with and without synephrine for 8 weeks on training adaptations in resistance-trained males. J Int Soc Sports Nutr. 2017;3;14:1. doi: 10.1186/s12970-016-0158- PubMed
  42. Jung YP, Earnest CP, Koozehchian M, et al. Effects of acute ingestion of a pre-workout dietary supplement with and without synephrine on resting energy expenditure, cognitive function and exercise performance. J Int Soc Sports Nutr. 2017;14:3. doi: 10.118
  43. Vatsavai LK, Kilari EK. Interaction of p-synephrine on the pharmacodynamic and pharmacokinetics of gliclazide in animal models. J Ayurveda Integr Med 2017; S0975-9476(16)30487-9. doi: 10.1016/j.jaim.2017.04.010.
  44. Ratamess NA, Bush JA, Stohs SJ, et al. Acute cardiovascular effects of bitter orange extract (p-synephrine) consumed alone and in combination with caffeine in human subjects: A placebo-controlled, double-blind study. Phytother Res. 2018;32(1):94-102.
  45. Gutiérrez-Hellín J, Ruiz-Moreno C, Del Coso J. Acute p-synephrine ingestion increases whole-body fat oxidation during 1-h of cycling at Fatmax. Eur J Nutr. 2019 Nov 5. PubMed
  46. Karimzadeh Z, Azizzadeh Forouzi M, Tajadini H, Ahmadinejad M, Roy C, Dehghan M. Effects of lavender and Citrus aurantium on pain of conscious intensive care unit patients: a parallel randomized placebo-controlled trial. J Integr Med 2021:S2095-4964(21)000 PubMed
  47. Koncz D, Tóth B, Bahar MA, Roza O, Csupor D. The Safety and Efficacy of Citrus aurantium (Bitter Orange) Extracts and p-Synephrine: A Systematic Review and Meta-Analysis. Nutrients 2022;14(19):4019. PubMed

See these in context on the Bitter Orange 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.

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