Quercetin · supplement
Evidence tier: weak
A natural mast cell stabiliser, particularly useful for allergies, histamine reactions, and prostatic inflammation.
Quercetin is a dietary flavonol. In laboratory work it stabilises mast cells and reduces histamine release, and it inhibits the NF-kB and MAPK inflammatory signalling pathways. This is cell and animal pharmacology. The step that has never been closed is showing those effects occur in people at supplement doses, which is the direct consequence of its poor oral bioavailability.
Weak. Memorial Sloan Kettering's About Herbs monograph states plainly that quercetin 'has not been shown to treat cancer or other diseases', and that is the honest headline for a molecule with a very loud marketing story. The blocking problem is pharmacokinetic before it is clinical: quercetin is poorly absorbed and heavily metabolised by glucuronidation, sulfation and methylation in the gut wall and liver, with only a few percent of an oral dose reaching the circulation as the parent compound, so the concentrations that produce mast cell stabilisation in a dish are not the concentrations a supplement produces in a person. On specific uses: for blood pressure a meta analysis of randomised trials (7 trials, 587 people, Journal of the American Heart Association 2016) found a small pooled reduction of about 3 mmHg systolic and 3 mmHg diastolic, which is a surrogate marker moving slightly, not a demonstrated health outcome. For exercise, meta analyses report trivial to small performance effects, with the clearer signal being reduced markers of muscle damage and soreness at around 1,000 mg daily. For allergic rhinitis the human literature is small, heterogeneous and mostly conducted with absorption enhanced derivatives such as enzymatically modified isoquercitrin rather than plain quercetin, and a 2025 systematic review of polyphenols in allergic rhinitis could not pool quercetin separately. There is no clinically established consumer indication.
No established therapeutic dose. Trials and supplement practice use 500 to 1,000 mg daily, often with vitamin C or bromelain on the theory of improved absorption, a theory that is asserted more often than it is tested.
500 to 1000 mg daily, often combined with vitamin C and bromelain for better absorption.
Generally well tolerated. May interact with cyclosporine, antibiotics, and tamoxifen.
Pregnancy: caution
Breastfeeding: caution
Active compounds: quercetin aglycone, isoquercitrin (quercetin-3-O-glucoside), rutin (quercetin-3-O-rutinoside), enzymatically modified isoquercitrin (EMIQ)
Remedies using Quercetin · Browse by body system · Check it against what you take
*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.