Quercetin
In plain terms: quercetin is a natural plant compound (a flavonol, one of the flavonoids) found in everyday foods such as onions, capers, apples, berries, kale, and tea. It is sold in the UK as a food supplement at 250–1000 mg/day. UK and EU authorities have not authorised any health claim for it, and it does not appear on NHS or NICE treatment pathways — so it is a dietary supplement, not a medicine. It can interact with prescription medicines through CYP3A4 inhibition, and supplemental forms are best avoided in pregnancy (dietary intake from food is not the concern).
Camden Medicals editorial · Last reviewed 3 May 2026 · Next review November 2026
- Cross-checked against
- NHS
- NICE
- BNF
- EFSA
- FSA
Camden's editorial team independently graded each health claim below on the strength of the published evidence — see the grade beside every condition.
- Class
- Polyphenol
- Typical daily dose
- UK retail products supply 250–1000 mg of quercetin (as dihydrate or formulated equivalents) per serving. Trials in BP / allergy / NAD-precursor contexts have used 500–1000 mg/day across 4–12 weeks. Camden NB-161 supplies 300 mg of quercetin per capsule (1-capsule serving) in a multi-active stack — at the lower end of the trial range.
- Top use evidence
- Limited
On this page
What it is
Quercetin is a flavonol — a sub-class of the flavonoid family of polyphenolic plant pigments. It is among the most widely distributed flavonoids in the human diet, present in significant concentrations in red onions (~5 mg/100 g raw), capers (~180 mg/100 g — the highest food source), kale, broccoli, cherries, blueberries, blackberries, apples (especially the skin), grapes, citrus fruits, and tea.
The aglycone form (free quercetin) is what UK retail supplements typically supply, often as quercetin dihydrate (a hydrated salt form with two water molecules per molecule of quercetin) — the most-bioavailable un-formulated salt. More-bioavailable formulations include Quercefit® (lecithin-phytosome by Indena), EMIQ (enzymatically modified isoquercitrin), and quercetin-rutin glycoside pairings. Plain quercetin aglycone has poor oral bioavailability — typically 1–5% of the oral dose reaches plasma — which is why formulation matters.
Quercetin has been studied for antioxidant activity (free- radical scavenging in vitro), anti-inflammatory activity (NF-κB pathway inhibition in vitro), antiviral activity (in some respiratory virus contexts at higher doses), antihistamine activity (mast-cell stabilisation in vitro), and for clearance of senescent ("worn-out") cells (in combination with dasatinib in the Kirkland / Mayo Clinic protocol; that combination is a research-context interventional drug protocol, not a food supplement).
Regulatory note: quercetin is lawful as a UK food supplement. There are no authorised UK food-supplement health claims for quercetin or for any specific flavonoid. EFSA has rejected most flavonoid claims at the EU evaluation stage on the grounds that "the food constituent is not sufficiently characterised". Antioxidant framing without a specific authorised claim is regulator-actionable; the conventional UK regulator-permissible framing is descriptive of the flavonol family and dietary sources.
At a glance
- A flavonol (yellow plant pigment) found in onions, capers, kale, apples, berries, and tea. Quercetin dihydrate is the most-bioavailable salt form for supplements.
- No UK-authorised food-supplement health claims. EFSA has rejected most flavonoid claims as "not sufficiently characterised". Antioxidant framing without a specific claim is problematic.
- Bioavailability is the principal supplement-design challenge. Quercefit® (lecithin-phytosome) substantially improves oral absorption vs unformulated quercetin dihydrate.
- Inhibits CYP3A4 at standardised supplement doses → drug-interaction implications. Talk to your prescriber if you take warfarin, ciclosporin, statins, or other CYP3A4-handled medication.
- Claims that quercetin "clears out old, worn-out cells" to reverse ageing are medicinal and prohibited on UK food supplements. Pregnancy: avoid supplemental form. Dietary intake from food is not the concern.
What people use it for
Adults exploring supplements for general antioxidant / inflammation support, alongside diet
Trials of quercetin (typically 500–1000 mg/day across 4–12 weeks) have reported various self-reported endpoints. UK food-supplement claims for antioxidant function from quercetin are not authorised — antioxidant framing without a specific claim is problematic. The conventional permissible framing is descriptive of the flavonol family + dietary sources.
Some evidenceLimitedAdults with seasonal-allergy / hay-fever symptoms, alongside NHS first-line options
Small trials of quercetin in seasonal allergy / allergic rhinitis have reported some self-reported endpoint changes. UK NHS first-line management is non-sedating antihistamines (loratadine, cetirizine, fexofenadine), nasal corticosteroids (beclometasone, fluticasone), and saline nasal rinses. Quercetin is not on UK NICE or NHS pathways. UK food-supplement claims for allergy from quercetin are not authorised. [2]
Some evidenceLimitedAdults exploring supplements for cardiovascular / blood-pressure support, alongside lifestyle
Small trials of quercetin in adults with elevated blood pressure have reported modest reductions in systolic / diastolic BP at 500–1000 mg/day across 8–12 weeks. UK NICE NG136 lists hypertension management — first-line lifestyle changes plus pharmacological options when indicated. Quercetin is not on those pathways. UK food-supplement claims for blood pressure from quercetin are not authorised. [3]
Some evidenceLimitedAdults considering quercetin in NAD-precursor stacks (with NMN / TMG)
Conventional in NAD-precursor stacks for putative complementary effects (anti-inflammatory + flavonoid contribution to redox balance). Camden NB-161 includes quercetin 300 mg per capsule alongside NMN, TMG, resveratrol, pterostilbene, and B12. The framing is mechanistic, not body-effect-claim-based.
Some evidenceLimitedAdults considering quercetin for diagnosed clinical conditions
Quercetin is not on UK NICE / NHS pathways for any specific clinical condition. Self-supplementation in place of formal management is not appropriate. Talk to your GP.
Popular, not provenInsufficient
How it works
Quercetin scavenges free radicals via multiple hydroxyl groups, modulates inflammation-pathway signalling (NF-κB inhibition in vitro), inhibits mast-cell degranulation (the in-vitro basis of antihistamine framing), and inhibits cytochrome-P450 enzymes (notably CYP3A4) and intestinal P-glycoprotein. The CYP3A4 / P-gp inhibition is the drug-interaction-relevant activity at standardised supplement doses.
Common myths
Myth"Quercetin is a "natural antihistamine""
RealityIn-vitro mast-cell-stabilisation activity has been reported for quercetin. Trial-level evidence in seasonal allergy is small and modest. UK NHS first-line allergy management is non-sedating prescription / pharmacy antihistamines, nasal corticosteroids, and saline rinses. The "natural antihistamine" framing exceeds the trial- level evidence and is not a UK-authorised claim. [2]
Myth"Quercetin clears out your old, worn-out cells and reverses ageing"
RealityThe idea that quercetin removes senescent ("worn-out") cells comes from the dasatinib + quercetin (D+Q) Kirkland / Mayo Clinic research protocol — a drug interventional protocol in clinical trials, NOT a food-supplement use case. Implying that a UK food supplement clears senescent cells is medicinal claim wording and is prohibited. UK food-supplement claims for lifespan-extension or rejuvenation are not authorised.
Myth"Plain quercetin powder is just as good as Quercefit® or EMIQ"
RealityPlain quercetin dihydrate has poor oral bioavailability (1–5% of dose reaches plasma). Formulated forms (Quercefit® lecithin-phytosome, EMIQ enzymatically modified isoquercitrin) substantially improve absorption and are what most modern trials use. Form matters for trial-comparable supplementation.
Myth"Quercetin is safe to combine with any medication because it's "natural""
RealityQuercetin inhibits CYP3A4 and intestinal P-glycoprotein at standardised supplement doses. The naturalness-as-safety framing is not appropriate; people on warfarin, ciclosporin, statins, and other CYP3A4 / P-gp-handled medication should disclose supplement use to their prescriber.
Myth"Quercetin treats COVID-19 / respiratory infections"
RealitySome early in-vitro and small-trial work explored quercetin in respiratory-virus contexts. UK NHS / NICE pathways for respiratory infection apply; quercetin is not on those pathways. Self-supplementation for diagnosed infection in place of clinical assessment is not appropriate. UK food-supplement claims for treating infection are prohibited.
Common online questions
Synthesised from the questions UK shoppers most often ask online about Quercetin. Each answer is editorial and links to its evidence in the Sources list below.
Can I just eat onions / apples / berries instead of taking quercetin supplements?
Dietary quercetin is the regulator-permissible framing — a balanced diet rich in onions, capers, apples (with skin), berries, kale, and tea supplies a few hundred milligrams of total flavonoid intake per day, including quercetin. Supplement doses (250–1000 mg of quercetin dihydrate) are higher than typical dietary intake. The "food first" framing is the conventional answer; supplement use is for those who want a higher, defined dose with awareness of the drug-interaction profile.
Quercetin dihydrate vs Quercefit® vs EMIQ — does it matter?
Bioavailability matters. Plain quercetin dihydrate has poor oral absorption (1–5% of dose reaches plasma). Quercefit® (lecithin-phytosome by Indena) reportedly improves bioavailability ~20-fold in pharmacokinetic trials. EMIQ (enzymatically modified isoquercitrin) is also more bioavailable than plain quercetin dihydrate. For trial-comparable supplementation, the formulated forms are what most modern trials use.
Is quercetin safe with prescription medication?
Talk to your prescriber. Quercetin inhibits CYP3A4 (the principal phase-I drug-metabolising enzyme) and intestinal P-glycoprotein at standardised supplement doses. Drug interactions to disclose: warfarin (possible additive bleeding), ciclosporin / tacrolimus (possible level changes), statins (simvastatin / atorvastatin — possible plasma rise), certain antibiotics (fluoroquinolones — absorption interaction), and chemotherapy agents handled by CYP3A4. Disclose use to your prescribing GP / pharmacist.
Does quercetin reverse ageing / make me live longer?
UK food-supplement claims for lifespan-extension or rejuvenation are not authorised. The idea that quercetin "clears out old, worn-out cells" comes from the Kirkland / Mayo Clinic dasatinib + quercetin (D+Q) RESEARCH-CONTEXT protocol — a drug interventional protocol in clinical trials, NOT a food-supplement use case. Implying that a UK food supplement clears senescent cells is medicinal claim wording and is prohibited.
Can I take quercetin while pregnant?
Standard advice is to avoid supplemental quercetin during pregnancy. Dietary quercetin from food is not the concern. Animal studies have raised some flags around prenatal flavonoid exposure at high doses; human pregnancy safety data for supplemental quercetin is limited. Talk to your GP if you have specific questions.
Will quercetin help my kidneys?
Talk to your GP. Quercetin has reported in-vitro effects on renal markers, but the evidence base is preclinical and outcome-trial data is limited. People with chronic kidney disease are advised to discuss any supplement with their nephrology team — there have been case reports of nephrotoxicity at very high quercetin doses (>1.5 g/day sustained), and supplement-medication interactions can affect renal handling.
🔬 Camden’s evidence review
The research Camden reviewed, graded on its strength. This is our own appraisal — it sits beneath the official guidance above, never above it.
Antioxidant / oxidative-stress markers
LimitedEvidencelimitedAuthoritative guidance leads here: EFSA assessed a quercetin oxidative-damage claim (ID 1647) and did not establish a cause-and-effect relationship, and the GB register authorises no antioxidant claim for quercetin. Camden's own evidence review, secondary to that position, finds in-vitro and small-trial data on oxidative-stress markers (MDA, 8-OHdG) reporting some changes at higher supplement doses, with limited translation to clinical-outcome improvement.
Allergic rhinitis / seasonal allergy
LimitedEvidencelimitedAuthoritative guidance leads here: the NHS hay-fever pathway (antihistamines, corticosteroid nasal sprays, saline rinses) and the BSACI rhinitis guideline, which judges the evidence for complementary and supplement-based approaches insufficient to recommend for clinical use. Quercetin is not a UK-recognised pathway and no allergy claim is authorised. Camden's own evidence review, secondary to that, finds small trials of quercetin in seasonal allergy reporting some self-reported nasal-symptom-score changes. [2]
Blood-pressure reduction in adults with elevated BP
LimitedEvidencelimitedAuthoritative guidance leads here: NICE NG136 sets out the recognised management of high blood pressure in adults (lifestyle advice plus a stepwise choice of antihypertensive medicines); quercetin is not on that pathway and no blood-pressure claim is authorised. Camden's own evidence review, secondary to that, finds small RCTs of quercetin 500–1000 mg/day reporting modest reductions in systolic / diastolic blood pressure, with small trial sizes. [3]
Senescent-cell-clearing activity (research context)
InsufficientEvidenceinsufficientAuthoritative guidance leads here: no UK guidance or authorised claim supports a senescent-cell or rejuvenation use of quercetin as a food supplement. Camden's own evidence review, secondary to that, notes the Kirkland / Mayo Clinic dasatinib + quercetin (D+Q) protocol is a RESEARCH-CONTEXT interventional drug protocol in clinical trials of cellular senescence in idiopathic pulmonary fibrosis and other age-related conditions — NOT a food-supplement use case. Supplement claim wording that quercetin clears senescent ("worn-out") cells is medicinal and prohibited.
CYP3A4 / P-glycoprotein inhibition — drug interaction
ModerateEvidencemoderateThis row is a drug-interaction SAFETY signal, not a benefit claim, so it sits alongside the authoritative-safety framing rather than under a guidance benefit stance. Camden's own evidence review finds multiple in-vitro and clinical- pharmacology studies characterising quercetin''s inhibition of CYP3A4 and intestinal P-glycoprotein at standardised supplement doses, informing interaction concerns for warfarin, ciclosporin, statins, certain antibiotics, and other CYP3A4 / P-gp-handled medication. Disclosure to a prescriber is the conventional safeguard. [5,6]
Safety
Quercetin from food is generally safe. Supplemental quercetin at standard doses (250–1000 mg/day) is generally well-tolerated short-term, with documented CYP3A4 / P-glycoprotein interactions affecting prescription medication. Pregnancy: avoid supplemental forms. Sustained doses >1.5 g/day raise nephrotoxicity concerns.
Talk to your pharmacist or GP first if you:
- You take warfarin or any vitamin-K-antagonist anticoagulant — possible additive bleeding via quercetin's CYP and platelet activity.
- You take ciclosporin / tacrolimus / mTOR inhibitors — possible plasma level changes via CYP3A4 / P-gp inhibition.
- You take statins (simvastatin, atorvastatin, rosuvastatin) — possible plasma level rise.
- You take certain antibiotics (fluoroquinolones — ciprofloxacin, levofloxacin) — quercetin can chelate fluoroquinolones and reduce absorption; separate by 4 hours.
- You take chemotherapy agents — possible level changes; defer to oncology team.
- You have chronic kidney disease — relative contraindication at sustained high doses.
- You are pregnant, breastfeeding, or trying to conceive — avoid supplemental form.
- You are under 18.
Common side effects: Mild GI complaints (nausea, abdominal discomfort) at higher doses. Headache occasionally reported. Generally well-tolerated short-term.
Pregnancy and breastfeeding
Avoid supplemental quercetin during pregnancy. Dietary intake from food is not the concern.
Avoid supplemental form. Limited human lactation safety data.
Talk to your GP, midwife, or pharmacist before starting any supplement during pregnancy or breastfeeding.
More clinical detail (for clinicians and informed readers)
Contraindications
- Pregnancy — avoid supplemental form (dietary intake from food is not the concern).
- Lactation — avoid supplemental form.
- Paediatric use — avoid as a supplement.
- Chronic kidney disease — relative contraindication at sustained high doses.
- Active liver disease — relative contraindication.
Drug interactions
- Warfarin and vitamin-K-antagonist anticoagulants — possible additive bleeding via CYP and platelet activity.
- Ciclosporin / tacrolimus / mTOR inhibitors — possible plasma level changes via CYP3A4 / P-gp inhibition.
- Statins (simvastatin, atorvastatin, rosuvastatin) — possible plasma level rise via CYP3A4 inhibition.
- Fluoroquinolones (ciprofloxacin, levofloxacin) — chelation reducing absorption; separate by 4 hours.
- Calcium-channel blockers (felodipine, nifedipine) — possible plasma level changes.
- Anti-epileptics (carbamazepine, phenytoin) — possible plasma level changes.
- Chemotherapy agents — possible level changes; defer to oncology team.
- Quinolone-class antibiotics — chelation interaction.
This is not an exhaustive list. Always tell your prescriber and pharmacist about every supplement you take.
Common side effects
- Mild GI complaints — nausea, abdominal discomfort; reduced by taking with food.
- Headache — occasionally reported at higher doses.
Rare side effects
- Allergic reaction.
- Tingling / paraesthesia at high doses (case reports).
- Nephrotoxicity — case reports at sustained doses >1.5 g/day; reversible on discontinuation.
How to take it
- Typical supplemental range
- UK retail products supply 250–1000 mg of quercetin (as dihydrate or formulated equivalents) per serving. Trials in BP / allergy / NAD-precursor contexts have used 500–1000 mg/day across 4–12 weeks. Camden NB-161 supplies 300 mg of quercetin per capsule (1-capsule serving) in a multi-active stack — at the lower end of the trial range.
- Timing
- Daily, with food. Lecithin-phytosome formulations (Quercefit®) reach plasma faster than plain quercetin dihydrate but the trial endpoints are still chronic (4–12 weeks).
How to spot quality
Look for
- Form declared: quercetin dihydrate (most-common UK supplement form) OR a more-bioavailable formulated form (Quercefit®, EMIQ).
- Bioavailability framing — modern trial-comparable products acknowledge that plain quercetin has poor absorption and use a formulated form.
- Dose declared per serving (mg of quercetin equivalent, not just mg of "quercetin complex").
- Country of manufacture stated.
- CoA available on request, with batch number and issue date.
- Heavy-metal screening disclosed.
- No "antioxidant" claim wording without an authorised claim — describe the flavonol family and dietary sources instead.
- No "clears senescent cells" / "worn-out cell removal" framing — that's medicinal-borderline language.
- Drug-interaction warning on label or PDP — quercetin's CYP3A4 / P-gp profile makes prescriber-disclosure prompts appropriate.
Red flags
- Generic "quercetin extract" without form / dose / source disclosure.
- Marketing as a "senescent-cell-clearing" or "worn-out-cell removal" supplement.
- Marketing as "natural antihistamine" / "natural antiviral" / "natural anti-inflammatory" — quasi-claim wording.
- Antioxidant claim without specific authorised wording.
- No CYP3A4 / drug-interaction warning despite standardised supplement dose.
- No pregnancy contraindication on supplement form.
- No country-of-manufacture or CoA disclosure.
- Sustained-dose recommendations >1.5 g/day without nephrotoxicity caveat.
Where Camden lands · gap declared
Quercetin is not a standalone Camden SKU. It appears in Camden's catalogue only as a co-ingredient in NB-161 (NMN Complex 90 Delayed Release Capsules), which supplies 300 mg of quercetin per capsule (1-capsule serving) alongside NMN, TMG, resveratrol, pterostilbene, and vitamin B12. That 300 mg sits at the lower end of the 500–1000 mg/day range used in standalone quercetin trials, and NB-161 supplies unformulated quercetin rather than a higher-bioavailability form (Quercefit®, EMIQ). The quercetin contribution in NB-161 is framed mechanistically as part of a multi-active stack, not as a standalone quercetin product, and no UK health claim attaches to the quercetin component.
Reformulation or supplier clarification is in progress.
Commonly combined with
Other ingredients that share a biological pathway, cofactor relationship, or evidence-backed protocol with this one. Mechanisms below cite primary physiology — not folk pairing. Doses are literature ranges, not recommendations. Talk to your pharmacist or GP before changing your stack, especially if you take prescription medication.
Resveratrol (trans-resveratrol)
Limited evidenceQuercetin + resveratrol is a classical polyphenol stack pairing — both polyphenols with overlapping in-vitro signalling effects. Camden NB-161 includes both.
Both quercetin (a flavonol) and resveratrol (a stilbene) have been studied in vitro for sirtuin / NF-κB signalling effects and antioxidant activity. The in-vitro mechanism framing is biochemically settled; outcome-trial evidence for the combination as such in humans is limited.
Evidence: Conventional in NAD-precursor / longevity stacks. Camden NB-161 supplies 300 mg quercetin + 170 mg trans-resveratrol per capsule. Combination outcome trials in humans are sparse.
Doses studied: Quercetin 300–500 mg + trans-resveratrol 100–250 mg daily.
Found in Camden: Clarifera™ NMN Complex 90 Delayed Release Capsules
NMN (β-Nicotinamide Mononucleotide)
Limited evidenceConventional in NAD-precursor stacks; quercetin contributes anti-inflammatory / flavonoid framing alongside NMN's NAD-precursor framing.
Quercetin and NMN target different pathways. Inclusion in NAD-precursor stacks is convention-driven. Outcome-trial evidence for the combination is sparse.
Evidence: Camden NB-161 supplies 300 mg quercetin + 500 mg NMN per capsule. NMN is on the FSA novel-food register as "pending"; this combination is discussed for mechanistic context.
Doses studied: Quercetin 250–500 mg + NMN 250–500 mg daily.
Found in Camden: Clarifera™ NMN Complex 90 Delayed Release Capsules
Verifera™ editorial perspective
Why it matters. Quercetin is a dietary flavonoid found in everyday foods and sold as a food supplement. Across UK and EU authorities no health claim for it is authorised and no NHS or NICE pathway includes it — so a consumer is choosing a dietary supplement, not a treatment.
Where Camden lands. Camden retails quercetin only as a co-ingredient in NB-161 (NMN Complex), not as a standalone product, and attaches no health claim to its quercetin content.
If you want to explore further. Authoritative UK and EU guidance leads this entry (the guidance section: GB NHC register, EFSA, NHS, NICE, BSACI); Camden's graded evidence review sits beneath it as a secondary 'our research' layer and never overrides it. For a specific condition, the relevant NHS pathway or a pharmacist is the authority to consult first.