Quercetin

Pronunciation: KWER-si-tin.

Generic name
quercetin
Drug class
Not applicable -- quercetin is a flavonoid antioxidant compound sold as a dietary/food supplement, not a regulated drug class
Form
Capsules, tablets, or powders, commonly 250 mg-1000 mg per serving
Route
Oral (capsule, tablet, or powder)
Legal status
Dietary/food supplement in the United States, United Kingdom, European Union, and New Zealand; a licensed low-risk complementary/natural-health product (Natural Health Product in Canada, 'Listed' AUST L medicine in Australia) -- not a prescription or pharmacy-only medicine in any of these 6 markets.

Availability and supply rules vary by country

Trade names by country: United States

Australia: · Full directory

What quercetin is and how it works

Quercetin is a plant flavonoid with antioxidant and anti-inflammatory properties, found naturally in many fruits and vegetables and sold separately as an over-the-counter dietary supplement. It is not a regulated prescription or pharmacy medicine in the US, UK, EU, Canada, Australia, or New Zealand. (1)

Quercetin supplements are marketed for a range of uses including allergy relief, general antioxidant support, and inflammation, but clinical trial evidence has not shown it to be effective for any specific medical condition. If you are considering quercetin for a health concern, especially alongside other medicines, it is worth discussing with a pharmacist or healthcare provider first.

Mechanism of action: how quercetin works

Quercetin is a flavonol with antioxidant and anti-inflammatory activity, partly via inhibition of cyclooxygenase enzymes, leukotriene/prostaglandin synthesis, and histamine release; it also inhibits certain cytochrome P450 enzymes (e.g. CYP3A4) and drug transporters (P-glycoprotein, OATP, BCRP, MRP2) in vitro, which underlies its potential drug interactions. Oral bioavailability is limited by extensive first-pass metabolism. (1) (5)

What quercetin is used for

General antioxidant / dietary supplement use

Marketed as a source of antioxidants that may help protect cells against oxidative damage from free radicals. This is a supplement-type structure/function claim, not a treatment claim for any diagnosed condition. (6)

Allergy and inflammation-related marketing claims (evidence limited)

Widely marketed for seasonal allergies, general inflammation, and cardiovascular health, but the National Center for Complementary and Integrative Health (NCCIH) states there is insufficient evidence that quercetin relieves allergic rhinitis symptoms, and NIH's LiverTox review notes it has not been shown effective in clinical trials for any medical condition studied so far, including cardiovascular disease and high cholesterol. (4) (1)

Traditional 'capillary/blood vessel protectant' use (Canada)

In Canada, quercetin may be licensed with a traditional herbal-medicine claim as a capillary/blood vessel protectant, per Health Canada's official supplement monograph -- this reflects an accepted traditional-use claim category, not proof of clinical efficacy from modern trials. (6)

Before taking quercetin

Do not take / not appropriate for

  • There is no specific contraindication required on quercetin supplement labelling in the sources reviewed for this dossier, but anyone with an allergy to quercetin or a supplement's other ingredients should avoid it. (all countries) (6)

Tell your clinician about

  • Whether you are pregnant, trying to become pregnant, or breastfeeding -- Health Canada's official supplement guidance specifically advises asking a healthcare practitioner before use in this situation for products providing 40 mg or more quercetin daily.
  • Any prescription medicines you take, especially antibiotics (particularly quinolone-type antibiotics), blood thinners such as warfarin, ciclosporin, or any medicine you know is broken down by liver enzymes, since quercetin may affect how these are processed by the body.
  • Any plans to use quercetin for more than about 12 weeks -- ask a healthcare practitioner first, per official Canadian supplement guidance.
  • Any kidney problems, since very high supplement doses have been associated with kidney effects in some reports.
(6) (5)

How to take quercetin

  • Quercetin supplements are typically taken by mouth with a meal or food, especially at doses of 40 mg or more per day, per official Canadian supplement guidance.
  • Follow the dose on the product label, since there is no single official prescribing dose -- products vary by manufacturer and formulation.
  • Discuss use beyond about 12 weeks with a healthcare practitioner rather than continuing indefinitely on your own.
  • If you take other medicines, ask a pharmacist whether quercetin is appropriate to combine with them.
(6)

Procedures and treatment changes

Tell the treating team before surgery, procedures, or any medicine change. Do not alter treatment without the responsible clinician. (1) (2) (3) (4) (5) (6) (7) (8) (9) (10)

Missed dose

Since quercetin is a supplement rather than a prescribed treatment with a strict dosing schedule, simply resume your usual routine at the next planned dose -- there is no medical urgency to a missed supplement dose.

Overdose

If a large amount has been taken accidentally, especially by a child, contact a poison control/information service or seek medical advice, since very high doses have been linked to symptoms such as headache, tingling in the arms and legs, and, rarely, kidney effects. (1)

Side effects

Side effects and their urgency vary; report severe, persistent, or concerning symptoms.

Generally well tolerated at typical supplement doses, with minimal reported adverse effects in clinical studies.

What to notice: Generally well tolerated at typical supplement doses, with minimal reported adverse effects in clinical studies.

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (1)

Headache and tingling sensations in the arms and legs have been reported by some users, particularly at higher doses.

What to notice: Headache and tingling sensations in the arms and legs have been reported by some users, particularly at higher doses.

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (1)

Mild stomach upset or nausea in some people.

What to notice: Mild stomach upset or nausea in some people.

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (1)

Serious warnings

Signs of a possible allergic reaction — emergency

Symptoms: Swelling of the face, lips, tongue, or throat; difficulty breathing; widespread rash or hives.

Action: Seek emergency medical help immediately and stop use under medical guidance. (6)

Reduced effectiveness of certain antibiotics or other medicines taken together with quercetin — high caution

Symptoms: No specific symptom -- this is a theoretical interaction concern based on laboratory mechanism studies (competition for bacterial DNA gyrase binding with quinolone antibiotics, and inhibition of certain liver enzymes/transporters relevant to drugs such as ciclosporin and warfarin), with uncertain real-world clinical significance.

Action: Tell your pharmacist or prescriber about quercetin use if you are taking a quinolone-type antibiotic, warfarin, ciclosporin, or other liver-enzyme-metabolised medicines, so they can advise on timing or whether to avoid combining them. (5)

Kidney effects reported with very high supplement doses — high caution

Symptoms: Reduced urination, swelling, or unusual fatigue.

Action: Seek medical advice if these occur, and avoid exceeding labelled supplement doses. (1)

Interactions

  • Quercetin has been shown in laboratory studies to inhibit certain liver enzymes (including CYP3A4) and drug transporters, which could theoretically increase blood levels of some medicines processed through these pathways, such as ciclosporin and warfarin -- tell your prescriber or pharmacist about quercetin use if you take these. (5)
  • A theoretical, uncertain-significance interaction with quinolone-type antibiotics (e.g. ciprofloxacin) has been described, based on a proposed shared binding mechanism -- evidence is mixed, with some laboratory studies instead showing quercetin may enhance certain antibiotics' activity, so this should be treated as a caution to discuss with a pharmacist rather than a settled harm. (5)

Pregnancy, breastfeeding, kidney/liver function, age

Pregnancy

Ask a healthcare practitioner before use if pregnant, per official Canadian supplement guidance -- robust safety data in human pregnancy is limited. (1) (2) (3) (4) (5) (6) (7) (8) (9) (10)

Breastfeeding

Ask a healthcare practitioner before use while breastfeeding, per official Canadian supplement guidance -- robust safety data during lactation is limited. (1) (2) (3) (4) (5) (6) (7) (8) (9) (10)

Children

Not established as a general supplement use for children in the sources reviewed for this dossier; the official Canadian monograph's dosing guidance applies to adults 18 years and older. (1) (2) (3) (4) (5) (6) (7) (8) (9) (10)

Elderly

No specific dose adjustment identified in the sources reviewed, though general caution around cumulative supplement use and interactions with prescribed medicines applies. (1) (2) (3) (4) (5) (6) (7) (8) (9) (10)

Hepatic_impairment

No specific restriction identified; quercetin itself is considered an unlikely cause of liver injury per LiverTox, though caution is reasonable given its effect on liver drug-metabolising enzymes. (1) (2) (3) (4) (5) (6) (7) (8) (9) (10)

Renal_impairment

Use caution and avoid very high doses given reports of kidney effects at high supplement intakes; discuss with a healthcare provider if you have kidney problems. (1) (2) (3) (4) (5) (6) (7) (8) (9) (10)

Monitoring

Before starting

  • Review of current prescription medicines for possible interactions
  • Confirmation there is no known allergy to quercetin or supplement excipients

During treatment

  • General awareness of any new symptoms, particularly if combining with prescription medicines.
  • Re-assessment with a healthcare practitioner if use continues beyond about 12 weeks.
(6)

Storage

Store as directed on the product label, typically at room temperature, away from moisture and heat, and out of reach of children.

Professional information

Clinician-facing context only, sourced from NIH LiverTox, NIH ODS, and Health Canada's official supplement monograph; quercetin is not a regulated drug so no formal prescribing information exists.

Canada (official supplement monograph)

Indication: Antioxidant support / traditional capillary-protectant use (supplement-level claims, not a treatment indication)

Dose summary: Antioxidant claim: up to 1200 mg/day, max 600 mg per single dose. Capillary/blood-vessel-protectant claim: 600-1200 mg/day, max 600 mg per single dose. Take with food for products providing 40 mg/day or more. Ask a healthcare practitioner for use beyond 12 weeks.

Renal context: Not specifically addressed in the monograph reviewed; general caution advised at high doses. (6)

Mechanism of action

Hepatic guidance

LiverTox assigns quercetin a hepatotoxicity likelihood score of E (unlikely cause of clinically apparent liver injury), with no published cases identified in major international drug-injury registries reviewed (1998-2015).

Overdose note

Limited overdose data; very high doses have been associated with headache, paresthesia, and rare reports of kidney effects -- manage supportively and seek guidance from a poison-information service if a large accidental ingestion occurs. (1) (5)

Frequently asked questions

Is quercetin a prescription medicine in the US, UK, Europe, Canada, Australia, or New Zealand?

No. In all 6 of these markets, quercetin is sold as a dietary/food supplement or a licensed low-risk complementary product (a Natural Health Product in Canada, a 'Listed' AUST L medicine in Australia) -- it is not a prescription or pharmacy-only medicine anywhere. (3) (8) (9) (6) (7) (10)

Does quercetin actually help with allergies or inflammation?

The evidence is limited. NCCIH states there is insufficient evidence that quercetin relieves allergic rhinitis symptoms, and NIH's LiverTox review notes that quercetin has not been shown effective in clinical trials for any medical condition studied so far, despite being marketed for allergies, inflammation, and cardiovascular health. It should not be treated as a proven treatment for any specific condition. (4) (1)

Can I take quercetin with my antibiotics or other prescription medicines?

Check with a pharmacist first. Quercetin can affect certain liver enzymes and transporters involved in processing some medicines (such as ciclosporin and warfarin), and a theoretical, uncertain-significance interaction with quinolone-type antibiotics has been described. This is a caution to discuss, not a proven serious harm, but it is worth checking before combining them. (5)

What is the mechanism of action of quercetin?

Quercetin is a flavonol with antioxidant and anti-inflammatory activity, partly via inhibition of cyclooxygenase enzymes, leukotriene/prostaglandin synthesis, and histamine release; it also inhibits certain cytochrome P450 enzymes (e.g. CYP3A4) and drug transporters (P-glycoprotein, OATP, BCRP, MRP2) in vitro, which underlies its potential drug interactions. Oral bioavailability is limited by extensive first-pass metabolism. (1) (5)

What is the generic name of Quercetin?

The generic name is quercetin. (1) (3)

What class of drug is quercetin?

Quercetin is classed as: Not applicable -- quercetin is a flavonoid antioxidant compound sold as a dietary/food supplement, not a regulated drug class. (1) (3)

References

  1. Quercetin -- LiverTox: Clinical and Research Information on Drug-Induced Liver InjuryLiverTox, National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) / National Library of Medicine (NIH), NCBI Bookshelf · United States · accessed 2026-07-30 · source 1
  2. Dietary Supplement Label Database -- quercetin product listingsNIH Office of Dietary Supplements (ODS) -- Dietary Supplement Label Database (DSLD) · United States · accessed 2026-07-30 · source 2
  3. Dietary Supplements -- FDA regulatory overviewU.S. Food and Drug Administration · United States · accessed 2026-07-30 · source 3
  4. Seasonal Allergies at a GlanceNational Center for Complementary and Integrative Health (NCCIH), part of NIH · United States · accessed 2026-07-30 · source 4
  5. Inhibitory Effects of Quercetin and Its Main Methyl, Sulfate, and Glucuronic Acid Conjugates on Cytochrome P450 Enzymes, and on OATP, BCRP and MRP2 TransportersPubMed Central (PMC), National Library of Medicine (NIH) -- peer-reviewed pharmacology study · not country-specific (mechanistic pharmacology evidence) · accessed 2026-07-30 · source 5
  6. Natural Health Product Monograph: QuercetinHealth Canada -- Natural Health Products Ingredients Database (NHPID) compendial monograph · Canada · dated 2026-01-30 · accessed 2026-07-30 · source 6
  7. Quercetin and Metagenics Quercetin Protect -- ARTG listed-medicine entriesTherapeutic Goods Administration (TGA), Australia · Australia · accessed 2026-07-30 · source 7
  8. Food supplements -- FSA business guidanceFood Standards Agency (FSA), United Kingdom · United Kingdom · accessed 2026-07-30 · source 8
  9. Food supplements -- EFSA topic page and Directive 2002/46/ECEuropean Food Safety Authority (EFSA) / EU food supplements legal framework (Directive 2002/46/EC) · European Union · accessed 2026-07-30 · source 9
  10. Regulation of Dietary SupplementsMedsafe (New Zealand regulator) · New Zealand · accessed 2026-07-30 · source 10

Brand names by country

Single-ingredient quercetin names are shown separately by country. Product availability, strengths, and supply rules can change; combination products are not included here.

Priority countries

United States

  • Quercetin Phenolic6 [hp_X]/mL · energique, inc.
View brands in additional countries.