Quercetin

Snapshot

Indications	Contraindications
Muscle damage after exercise¹ Hepatic fat in fatty liver disease² Early COVID-19 adjunct³ Post-exercise oxidative stress¹ Vascular inflammation in men with CAD^4–6	Warfarin therapy

Quercetin is a flavonoid found in apples, onions, tea, and citrus, and the most common one in the human diet; it acts as an antioxidant and dampens inflammatory signaling, including histamine release. Supplementation is used for oxidative stress and inflammation, exercise-induced muscle damage and recovery, and metabolic and liver health. It is also taken for allergy-type and mast cell complaints and for viral respiratory illness, where trials are few. Active adults, people with metabolic liver disease, and patients seeking mast cell support make up the typical users.

Human research is limited to a modest number of mostly small trials, covering muscle damage after exercise, fatty liver, COVID-19, and respiratory disease. In 2021, open-label trials in outpatients with early COVID-19 reported faster viral clearance with a phytosome form of quercetin; no placebo-controlled trial has confirmed it. Products include capsules, powders, and tablets, often paired with bromelain or vitamin D, and forms differ in absorption; see Form comparison.

Last updated October 15, 2026. Read how we make monographs.

In the full monograph

58 sources, 45 studies

When to useThe situations practitioners use it for, each with the reason and the study behind it.
SafetyWho should avoid it, who needs extra care, and the side effects reported in studies.
InteractionsThe medicines and supplements it interacts with, the effect of each, and what labeling says to watch.
Protocol notesThe doses used in studies, how and when they were taken, and how the forms on the market compare.
How it worksWhat it is and how it works in the body, in plain terms.
Published studiesThe studies behind each use, popular claims checked against them, and trials still under way.
Word of mouthWhat patients and practitioners report online, kept separate from the clinical evidence.
Clinical perspectiveA closing read of where the evidence is solid, where it is thin, and what has not been studied.

Snapshot

In the full monograph

Sources