Quercetin

Also known as quercitin, quercetin dihydrate.

Last reviewed October 9, 2026 · Jump to references

What is Quercetin?

In plain words

Quercetin is a natural plant compound found in foods such as onions, apples, and berries. The body absorbs some of it and changes it into other compounds, which are eventually cleared in urine and bile. Researchers study it for effects on inflammation, allergies, and heart health, but studies in people have not established clear treatment benefits. Supplements can interact with medicines, and long-term safety at high intakes is not well established.

Technical definition

Quercetin is a plant-derived polyphenol in the flavonol class, with a three-ring structure bearing five hydroxyl groups; quercetin dihydrate is its crystalline form containing two water molecules per quercetin molecule. It has no single established therapeutic receptor target, but laboratory studies show effects on oxidative reactions, inflammatory signaling, and multiple enzymes; after ingestion, it is extensively converted to glucuronide, sulfate, and methylated metabolites. Quercetin is marketed as a dietary supplement in the United States and is not FDA-approved to treat or prevent disease.

Educational information only. This page does not provide medical advice or determine whether a supplement is appropriate for you. Review supplements with a qualified healthcare professional, especially if you take medication, are pregnant, have surgery scheduled, or have a chronic medical condition.

Evidence by use

Each use is rated on its own. There is no single overall effectiveness score.