Quercetin and medications.
Quercetin is in the Distil supplement database, evidence Grade B. The page below lists every medication we have explicitly assessed it against.
Quercetin is a plant flavonoid found in onions, apples and capers, and it turns up most often in allergy and immune stacks. We no longer offer it for immunity: the large null trial behind that decision is described below, and the one positive infection result in our records came from trained cyclists during a block of very hard exercise, which is not a situation our questionnaire can identify. Its senolytic role is Grade C, so the anti-ageing claims are among the weakest parts of the picture. The clearest benefit in our records is hay fever: a placebo-controlled trial in 66 adults with pollen allergy found that the phytosome form may ease itchy eyes, sneezing, a runny nose and disturbed sleep, and an independent review of 13 trials points the same way, though it pools several plant polyphenols rather than quercetin alone and rates its own certainty as low. Worth knowing before you weigh that: the 66-person trial was commissioned and paid for by the company that makes the phytosome product it tested, one of its authors works for that company, and it used 200mg, which is below the 500 to 1,000mg usually sold. We still grade this the lowest grade we recommend at, and it is the thinnest claim on this page. Mast cell stabilisation is the proposed explanation for that, rather than something anyone has measured in these trials. There is also a modest blood pressure effect: two separate reviews of the trials agree on a fall of roughly 2 to 3 mmHg, while finding no change in cholesterol or blood sugar, so it is a blood pressure finding and not heart protection. One thing our records do not support is respiratory infection. The largest trial of this compound in the indexed literature, in 1,002 adults taking 500mg or 1,000mg daily for 12 weeks, found no effect on how often people caught a cold or how bad it was. Bioavailability is the catch: ordinary quercetin absorbs very poorly, so the phytosome form at 500 to 1,000mg is the one worth taking. The interaction list is where care is needed. Quercetin can interfere with fluoroquinolone antibiotics, and it should be excluded in transplant patients without their team's approval. The direction there runs the opposite way to most supplement interactions, and it is worth being clear about: three animal studies found ciclosporin absorption falling by roughly 15 to 55 percent when quercetin was given alongside it, so the concern is too little of the transplant medicine rather than too much, and a level that drops too low can let the body begin rejecting a transplant. Whether quercetin inhibits or induces CYP3A4 is genuinely contested, which is why we describe the fall we can observe rather than assert an enzyme mechanism: the two human studies in our records point toward faster clearance of orally dosed drugs, while laboratory work points the other way. It should also be avoided by anyone on antiretroviral therapy for HIV, where the same uncertainty applies to medicines that need steady levels. At high doses it has mild antiplatelet activity and may affect warfarin metabolism, so flag it to your GP and monitor INR if you take an anticoagulant. It pairs well with vitamin C. Practically, separate it from those drug classes and review with a prescriber first.
Below are the 16 documented pairs we have explicitly assessed for Quercetin: 4 red and 12 amber. The pairs cluster around 5 mechanisms: Reduced immunosuppressant level, Additive anticoagulation, CYP-mediated metabolism, CYP3A4 inhibition, and P-glycoprotein inhibition (raises drug levels). Every call is cited to either a clinical reference (PMID) or the British National Formulary. Anything not listed here is either still to be assessed or beyond our database scope. The checker beneath surfaces assessments by medication, and the missing-item form at the bottom of the page routes any uncatalogued medication into our next curation pass.
Documented interactions
Last reviewed 27 August 2026. Each interaction below lists the evidence its assessment drew on: some rest on studies of the exact pair, others on mechanism evidence, where a citation may support one part of the reasoning rather than the exact combination. The evidence line on each entry says which.
Reduced immunosuppressant level
Red Does Quercetin interact with Ciclosporin?
Quercetin supplements may lower ciclosporin blood levels, so if you take ciclosporin do not start quercetin without speaking to your transplant team first. The concern runs the opposite way to most supplement interactions: the risk is too little ciclosporin rather than too much, and a fall in level can let the body begin rejecting a transplant. Three animal studies found ciclosporin absorption falling by roughly 15 to 55 percent when quercetin was given alongside it, and none of this has been tested in people, so we treat it as a combination to avoid rather than one to watch.
Evidence: Limited human data, from small studies or case reports.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
Red Does Quercetin interact with Everolimus?
Quercetin supplements may lower everolimus blood levels, so if you take everolimus do not start quercetin without speaking to your transplant team or oncology team first. The concern runs the opposite way to most supplement interactions: the risk is too little everolimus rather than too much, and a fall in level can let the body begin rejecting a transplant or can weaken the treatment everolimus is being given for. No study has tested quercetin with everolimus in people or in animals, so this caution comes from what quercetin does to ciclosporin, a medicine handled by the same enzyme and transporter route, rather than from any measured effect on everolimus itself.
Evidence: No direct study of this exact combination yet; the caution rests on a plausible mechanism or on reports involving a related medicine.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
Red Does Quercetin interact with Sirolimus?
Quercetin supplements may lower sirolimus blood levels, so if you take sirolimus do not start quercetin without speaking to your transplant team first. The concern runs the opposite way to most supplement interactions: the risk is too little sirolimus rather than too much, and a fall in level can let the body begin rejecting a transplant. No study has tested quercetin with sirolimus in people or in animals, so this caution comes from what quercetin does to ciclosporin, a transplant medicine handled by the same enzyme and transporter route, rather than from any measured effect on sirolimus itself.
Evidence: No direct study of this exact combination yet; the caution rests on a plausible mechanism or on reports involving a related medicine.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
Red Does Quercetin interact with Tacrolimus?
Quercetin supplements may lower tacrolimus blood levels, so if you take tacrolimus do not start quercetin without speaking to your transplant team first. The concern runs the opposite way to most supplement interactions: the risk is too little tacrolimus rather than too much, and a fall in level can let the body begin rejecting a transplant. No study has tested quercetin with tacrolimus in people or in animals, so this caution comes from what quercetin does to ciclosporin, a closely related transplant medicine, rather than from any measured effect on tacrolimus itself.
Evidence: No direct study of this exact combination yet; the caution rests on a plausible mechanism or on reports involving a related medicine.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
Additive anticoagulation
Amber Does Quercetin interact with Acenocoumarol?
High-dose quercetin may mildly add to the blood-thinning effect of acenocoumarol. The signal is weak. If you take acenocoumarol and use quercetin supplements, mention it to your anticoagulant clinic and watch for bruising.
Evidence: No direct study of this exact combination yet; the caution rests on a plausible mechanism or on reports involving a related medicine.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
Amber Does Quercetin interact with Warfarin sodium?
Quercetin may, in theory, add to warfarin's blood-thinning effect at high doses, though a small human study found no change in INR. If you take warfarin, mention any high-dose quercetin to your GP and monitor your INR if you start it.
Evidence: Limited human data, from small studies or case reports.
CYP-mediated metabolism
Amber Does Quercetin interact with Efavirenz?
Quercetin supplements may shift efavirenz levels, and of the HIV medicines we assess this is the one we know least about, so if you take efavirenz do not start quercetin without telling your HIV team first. Efavirenz is cleared mainly by a liver enzyme that has never been tested with quercetin in any study, and it is taken without a booster drug, which leaves it more exposed than the protease inhibitors. A fall in efavirenz level can let HIV become resistant, so viral load is what your team would keep an eye on.
Evidence: No direct study of this exact combination yet; the caution rests on a plausible mechanism or on reports involving a related medicine.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
CYP3A4 inhibition
Amber Does Quercetin interact with Atorvastatin?
Quercetin may slow how the body clears atorvastatin via CYP3A4, which can raise atorvastatin levels. Watch for muscle pain or unusual fatigue and tell your GP if you take both regularly.
Evidence: No direct study of this exact combination yet; the caution rests on a plausible mechanism or on reports involving a related medicine.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
Amber Does Quercetin interact with Simvastatin?
Quercetin may slow how the body clears simvastatin via CYP3A4. Because simvastatin is more sensitive to CYP3A4 inhibition than atorvastatin, the effect may be larger. Watch for muscle pain and tell your GP if you take both.
Evidence: No direct study of this exact combination yet; the caution rests on a plausible mechanism or on reports involving a related medicine.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
P-glycoprotein inhibition (raises drug levels)
Amber Does Quercetin interact with Digoxin?
Quercetin may slow how the body clears digoxin by blocking a transporter pump (P-glycoprotein), which can push digoxin levels higher. Digoxin has a narrow safe range, so if you take it, speak to your GP before adding quercetin and do not start a high-dose supplement without that conversation.
Evidence: No direct study of this exact combination yet; the caution rests on a plausible mechanism or on reports involving a related medicine.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
Amber Does Quercetin interact with Fexofenadine hydrochloride?
Quercetin can raise blood levels of fexofenadine by blocking a transporter pump (P-glycoprotein). Fexofenadine is a low-risk antihistamine, so this rarely causes problems, but if you take both regularly and notice more drowsiness or side effects, separating them or lowering the quercetin dose is reasonable.
Evidence: Supported by human study data.
What this list does not say. Pairs not flagged here are not implicitly safe. They are either not yet in our database, or fall outside our inclusion scope. Use the checker below to surface any medication, and submit a missing item if you take something we have not catalogued.
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How we grade severity, choose what's in scope, and what we exclude.
Every call on this page is reasoned. We publish the full rubric for severity tiers, the medication inclusion logic, the evidence grades we accept, and what we deliberately leave out. About three thousand words. Worth reading once if you use this tool more than occasionally.
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The free checker answers one interaction question at a time. A Distil report reviews the bigger picture: your goals, diet, medications, current supplements and any blood results you provide, then shows what appears worth keeping, changing, adding or leaving out.
- what your diet already covers, so you are not adding a capsule for something food is already handling
- which evidence-graded compounds are worth considering for your goals, and which were considered but left out
- what to keep, change or stop from what you already take, plus the order to introduce anything new
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The interaction check is one section of the full report. You also get the reasoning behind each recommendation and the evidence references used.
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