{"ok":true,"entry":{"slug":"quercetin","kind":"supplement","name":"quercetin","aliases":["quercetin dihydrate","quercetin phytosome"],"brands_sg":["California Gold Nutrition","NOW Foods","Doctor's Best","Thorne","Life Extension"],"class":"flavonoid","tags":["immune","heart"],"use_for":"unclear — immune data is in animals, heart data is small","use_after":null,"use_duration":"trials ran 1 to 8 weeks · nothing longer has been studied","take_with":"sold with bromelain in sg · no evidence found for that pair","pros":["ods: no side effects at 1,000 mg/day for 2 months","fda: up to 500 mg per serving is gras in foods","human trials exist — 17 rcts, 896 people, pooled"],"cons":["immune evidence is preclinical — animals, not people","ods: performance effect trivial to none, inconsistent","safety above 1,000 mg, or past 2 months, is unstudied"],"dose_note":"the trials nih ods describes most often used 1,000 mg a day for 1 to 8 weeks; ods reports no side effects or safety concerns at that amount for up to 2 months and says longer-term use of that amount or more has not been studied, and fda treats up to 500 mg per serving as generally recognised as safe in foods; the 2020 meta-analysis of 17 trials in 896 people found lipid profiles and glucose unchanged and a small pooled blood-pressure difference, against a background of conflicting earlier trials","dosage":{"ul":null,"unit":"mg","fda_dv":null,"rda_ai":null,"ul_status":"none_established","population":"general adult","hsa_max_daily":null},"ul_status":"none_established","sg_class":null,"cautions":["above 1,000 mg a day, or past 2 months — ods: not studied","phytosome forms — the 1,000 mg safety figure is for plain quercetin","quercetin is not listed in hsa annex a or b — hsa says that list is not exhaustive","background diet already supplies flavonols — nhanes averaged about 13 mg a day"],"clashes":[],"sources":[{"id":"nih_ods_quercetin_trials","url":"https://web.archive.org/web/20260801175407/https://ods.od.nih.gov/factsheets/ExerciseAndAthleticPerformance-HealthProfessional/","label":"NIH ODS — Dietary Supplements for Exercise and Athletic Performance, Quercetin (Efficacy); ods.od.nih.gov returned Cloudflare 403 to a direct fetch, so the 1 Aug 2026 archive.org capture was read","quote":"These studies typically examined the endurance performance and VO2max of participants engaged in aerobic activities … who received either quercetin (most often 1,000 mg/day) or placebo for 1 to 8 weeks","accessed":"2026-08-27"},{"id":"nih_ods_quercetin_effect","url":"https://web.archive.org/web/20260801175407/https://ods.od.nih.gov/factsheets/ExerciseAndAthleticPerformance-HealthProfessional/","label":"NIH ODS — Exercise and Athletic Performance, Quercetin (what the trials showed) (archive.org capture, 1 Aug 2026)","quote":"The effects of quercetin supplementation were inconsistent and varied by study, but they generally ranged from no ergogenic benefit to only a trivial or small improvement that might not be meaningful in real-world … exercise conditions","accessed":"2026-08-27"},{"id":"nih_ods_quercetin_safety","url":"https://web.archive.org/web/20260801175407/https://ods.od.nih.gov/factsheets/ExerciseAndAthleticPerformance-HealthProfessional/","label":"NIH ODS — Exercise and Athletic Performance, Quercetin (Safety) (archive.org capture, 1 Aug 2026)","quote":"took as much as 1,000 mg/day quercetin for up to 2 months found no side effects or safety concerns. The safety of longer term use of that amount of quercetin or more has not been studied.","accessed":"2026-08-27"},{"id":"nih_ods_quercetin_gras","url":"https://web.archive.org/web/20260801175407/https://ods.od.nih.gov/factsheets/ExerciseAndAthleticPerformance-HealthProfessional/","label":"NIH ODS — Exercise and Athletic Performance, Quercetin (FDA GRAS status in foods) (archive.org capture, 1 Aug 2026)","quote":"FDA considers up to 500 mg/serving quercetin to be generally recognized as safe (GRAS) as an ingredient in foods such as beverages, processed fruits and fruit juices, grain products, pastas, and soft candies","accessed":"2026-08-27"},{"id":"nih_ods_quercetin_intake","url":"https://web.archive.org/web/20260801175407/https://ods.od.nih.gov/factsheets/ExerciseAndAthleticPerformance-HealthProfessional/","label":"NIH ODS — Exercise and Athletic Performance, Quercetin (dietary intake, NHANES 1999–2002) (archive.org capture, 1 Aug 2026)","quote":"An analysis of NHANES 1999–2002 data found that estimated daily total flavonol (including quercetin) consumption by adults averaged about 13 mg/day","accessed":"2026-08-27"},{"id":"huang2020","url":"https://europepmc.org/article/MED/31940027","label":"Effect of quercetin supplementation on plasma lipid profiles, blood pressure, and glucose levels: a systematic review and meta-analysis (Nutrition Reviews 2020; PMID 31940027)","quote":"Clinical trials examining the cardiovascular protective effects of quercetin in humans have reported conflicting results … Seventeen trials (n = 896 participants total) were included … Neither lipid profiles nor glucose concentrations changed significantly.","accessed":"2026-08-27"},{"id":"dominguez2021","url":"https://europepmc.org/article/PMC/PMC8250479","label":"Effectiveness of supplementation with quercetin-type flavonols for treatment of viral lower respiratory tract infections: systematic review and meta-analysis of PRECLINICAL studies (Phytotherapy Research 2021; PMC8250479)","quote":"we conducted a systematic review to describe the use of quercetin-type flavonols against lower respiratory tract viruses and discussed the preclinical impact … significantly reduced mortality rate … of infected animals","accessed":"2026-08-27"},{"id":"hsa_prohibited_2025","url":"https://file.go.gov.sg/hsa-chp-prohibited-restricted-ing-guidelines.pdf","label":"HSA Singapore — Guidelines on Prohibited and Restricted Ingredients in HS and TM, GL-CHPB-1-012 Rev. No. 001 (October 2025), clause 1.3 + Annexes A and B","quote":"The objective of this guideline is to highlight the substances of concern when used in HS and TM and is not meant to be an exhaustive list [quercetin not listed in Annex A or B]","accessed":"2026-08-27"},{"id":"iherb_sg","url":"https://sg.iherb.com/c/quercetin","label":"iHerb Singapore — Quercetin category, default order (1 - 48 of 145 results)","quote":"California Gold Nutrition, NMN Complex with trans-Resveratrol, Quercetin Phytosome Complex … NOW Foods, Quercetin with Bromelain … NOW Foods, Quercetin, 500 mg … Doctor's Best, Quercetin Bromelain … Thorne, Quercetin Phytosome … Life Extension, Bio-Quercetin®","accessed":"2026-08-27"}],"brand_certs":[{"brand":"Thorne","example":null,"programme":"NSF Certified for Sport","matching_products":0,"brand_total_certified":66}],"updated_at":"2026-08-30T17:59:38.376296+08:00"},"disclaimer":"kozen-x is not a medical device and does not give medical advice. it lists what published sources have written down. absence of a record is not the same as safe."}