Quercetin has 2 documented interactions in Magellan’s curated dataset, covering Chemotherapy and cancer therapy, Antiplatelet drugs, Immunosuppressants. Each entry below gives the mechanism as the cited reference states it, the direction the risk runs, how serious that reference treats it, and what to actually do about it — which is, in every case, a conversation with the clinician or pharmacist who manages the prescription rather than a decision you make alone.
What it is. Quercetin is a flavonol, a plant polyphenol found abundantly in onions, apples, berries, capers, and tea. As one of the most common dietary flavonoids, it has antioxidant and anti-inflammatory properties and has been investigated for cardiovascular effects, particularly on blood pressure.
Where it sits on the evidence. Magellan grades the supplement itself as Moderate evidence, with a typical studied dose of ≥500 mg/day (blood-pressure effects appear mainly at 500 mg/day and above). That grade is about whether it works, not about whether it is safe alongside your medication — the two questions are independent, and this page answers only the second.
Products this covers: Quercetin Capsules.
How the risks cluster. The entries split across 2 different mechanisms — opposing; bleeding risk — and they are not managed the same way, so read each one rather than assuming a single rule covers all of them.
Safety and efficacy are separate questions, and this page only answers the first. For the second, the study Magellan’s coverage of Quercetin rests on is:
“quercetin supplementation significantly decreased systolic blood pressure”
A strong result does not make a supplement safe alongside your prescription, and a documented interaction does not mean the supplement does not work. Magellan grades those two things separately, and neither grade moves for a commission.
Magellan’s Medication Safety Check runs entirely on your device — type the medicines you take and it flags every documented interaction in this dataset. Nothing you type is sent anywhere.
Open the Medication Safety Check →NCCIH advises that antioxidant supplements may reduce the effectiveness of cancer treatments that work by generating reactive oxygen species, and recommends checking with the oncology care team before use; quercetin is a potent dietary antioxidant/flavonoid, so this general antioxidant-supplement caution is relevant.
Medicines in this group include: Methotrexate (Trexall, Otrexup), Tamoxifen (Nolvadex), Cisplatin, Doxorubicin (Adriamycin), Vincristine (Oncovin), Bortezomib (Velcade), Cyclophosphamide (Cytoxan).
Quercetin has documented in-vitro antiplatelet activity and inhibits CYP3A4/P-glycoprotein, which could theoretically raise blood levels of drugs like cyclosporine or add to bleeding risk with blood thinners.
Medicines in this group include: Aspirin (Asa, Bayer aspirin), Clopidogrel (Plavix), Ticagrelor (Brilinta), Prasugrel (Effient), Dipyridamole (Aggrenox, Persantine), Cyclosporine (Neoral, Sandimmune), Tacrolimus (Prograf, Astagraf), Sirolimus (Rapamune, Rapamycin) and 2 more.
These are the warning signs that go with the medication classes on this page. They are general safety-netting, not a prediction that any supplement will cause them.
If something feels seriously wrong, do not wait for an appointment. Call 911 (US) or your local emergency number.
Severity describes the interaction as the cited reference frames it, not how a specific person will react. A “minor” entry in someone with kidney disease, on five other drugs, can matter more than a “major” one in someone on nothing else.
This is a curated set of interactions with citations — not an exhaustive pharmacology database. An interaction that is absent here has not been ruled out; it may simply not be documented in the references Magellan curates from. Supplements are also not batch-tested for identity or contamination the way prescription drugs are, so what is on the label is a claim rather than a guarantee. And most of these entries come from case reports and mechanistic work rather than randomized trials, which is exactly why the sensible response is a pharmacist review rather than either alarm or dismissal.
9 documented interactions across 9 supplements.
22 documented interactions across 17 supplements.
7 documented interactions across 7 supplements.
3 documented interactions · shares a drug class with Quercetin.
3 documented interactions · shares a drug class with Quercetin.
8 documented interactions · shares a drug class with Quercetin.
7 documented interactions · shares a drug class with Quercetin.
The mechanism and the research behind the compound itself.
A–Z of every supplement and drug class in this dataset, plus how to read an interaction.
What the research actually shows, graded independently of affiliate commissions.
Not without checking with the prescriber or pharmacist first. Magellan's dataset grades this as a moderate interaction: NCCIH advises that antioxidant supplements may reduce the effectiveness of cancer treatments that work by generating reactive oxygen species, and recommends checking with the oncology care team before use; quercetin is a potent dietary antioxidant/flavonoid, so this general antioxidant-supplement caution is relevant. (Source: Antioxidants: In Depth.)
2 interactions are documented in Magellan's curated dataset: 1 moderate, 1 minor. They cover Chemotherapy and cancer therapy, Antiplatelet drugs, Immunosuppressants. Absence from this list is not proof of safety — it means no interaction is documented in the references we curate from.
Magellan lists the typical studied dose as: ≥500 mg/day (blood-pressure effects appear mainly at 500 mg/day and above). Dose matters for interactions — several of the entries on this page describe effects that only appear at supplemental rather than dietary intakes.