{"entity":{"id":"quercetin-supplements","kind":"technology","name":"Quercetin supplements","aka":["Quercetin"],"tldr":"Quercetin is a flavonoid found in apples, onions and tea, sold as an antioxidant and anti-cancer supplement. There is no human evidence that it treats or prevents cancer, it made oestrogen-driven breast tumours worse in mice, and it may raise levels of some drugs, including tamoxifen in laboratory studies and warfarin in one patient.","summary":"Memorial Sloan Kettering's About Herbs entry describes antioxidant, anti-inflammatory and chemopreventive effects of quercetin in cell studies, alongside an anti-apoptotic action that could protect cells. Human studies are mostly in exercise, metabolism and rheumatoid arthritis. In cancer, quercetin has been identified as one of many components of traditional Chinese formulas analysed in meta-analyses, which does not isolate its effect; dietary quercetin was not associated with lower ovarian cancer risk, and in a mouse model it exacerbated oestrogen-induced breast tumours. Laboratory studies show inhibition of CYP3A4 and CYP2C19 and increased tamoxifen bioavailability, with clinical relevance unknown; a man on stable warfarin developed a raised INR after starting quercetin that returned to normal after stopping.","status":"phase-2","asOf":"2026-11-04","links":[{"label":"MSK About Herbs: Quercetin (page last updated 10 October 2023)","url":"https://www.mskcc.org/cancer-care/integrative-medicine/herbs/quercetin"}],"tags":["complementary","supportive-care","evidence:insufficient"],"related":["resveratrol-supplements","flaxseed-supplements"],"cancers":[],"sections":["supportive-care","nutrition-lifestyle"],"technologies":["integrative-oncology","dietary-supplements-treatment-interactions"],"targets":[],"drugs":["tamoxifen"],"companies":[],"institutions":[],"pathways":[],"terms":["unproven-diet-claims"],"trials":[],"people":[],"bottlenecks":["b-misinformation"],"keyPapers":[],"journals":[],"dependsOn":[],"notes":[],"principle":"A flavonol that scavenges free radicals and inhibits kinases and drug-metabolising enzymes in vitro; low and variable absorption in people.","strengths":["Common in a healthy diet"],"limitations":["No human cancer evidence","Worsened oestrogen-driven tumours in mice","Possible interactions with tamoxifen and warfarin"]},"route":"/technologies/quercetin-supplements/","neighbours":{"technology":[{"id":"dietary-supplements-treatment-interactions","kind":"technology","name":"Dietary supplements during cancer treatment: interactions and harms","route":"/technologies/dietary-supplements-treatment-interactions/"},{"id":"integrative-oncology","kind":"technology","name":"Evidence-based integrative oncology","route":"/technologies/integrative-oncology/"},{"id":"flaxseed-supplements","kind":"technology","name":"Flaxseed and flaxseed lignans","route":"/technologies/flaxseed-supplements/"},{"id":"resveratrol-supplements","kind":"technology","name":"Resveratrol supplements","route":"/technologies/resveratrol-supplements/"}],"section":[{"id":"nutrition-lifestyle","kind":"section","name":"Diet, Exercise & Lifestyle","route":"/fronts/nutrition-lifestyle/"},{"id":"supportive-care","kind":"section","name":"Supportive Care & Survivorship","route":"/fronts/supportive-care/"}],"drug":[{"id":"tamoxifen","kind":"drug","name":"Tamoxifen","route":"/drugs/tamoxifen/"}],"term":[{"id":"unproven-diet-claims","kind":"term","name":"Unproven diet claims (alkaline, juice, 'anti-cancer' diets)","route":"/terms/unproven-diet-claims/"}],"bottleneck":[{"id":"b-misinformation","kind":"bottleneck","name":"Misinformation and unproven therapies","route":"/bottlenecks/b-misinformation/"}]}}