Herbs & botanicals
Quercetin
Names you may see: quercetin dihydrate flavonoid polyphenol
The quick take
Quercetin is a flavonoid found in foods such as onions, apples and berries.
A closer look
What forms will I see on a label?
Labels may list quercetin, quercetin dihydrate or a delivery-system blend. Compare the actual quercetin amount.
Why people use it
People choose it for antioxidant, seasonal-allergy and exercise-recovery goals.
These are common goals and marketing uses. The evidence section below explains what research supports.
What does the evidence tell us?
Laboratory findings are promising, but human evidence varies by outcome and formulation. Small studies do not establish broad protection against illness or reliable allergy relief.
What should I know before using it?
Quercetin can affect drug-metabolizing enzymes and may interfere with some cancer treatments. Discuss concentrated supplements with a pharmacist or treating clinician if taking medicines.
Sources & further reading
Content reviewed: September 30, 2026
General educational information. Follow the product label and seek individual advice when needed.