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Quercetin
A plant compound found in onions, apples, berries and tea, sold on its own and in products advertised for general health, weight loss and body building.
Explained simply · Last reviewed
What it is
Quercetin is a plant compound, one of the flavonoids, found in many foods and herbs. LiverTox, the US government reference on drug-induced liver injury, says it is a regular part of a normal diet, found in high amounts in apples, berries, onions, broccoli and tomatoes, and in herbs such as ginkgo, St John's wort and milk thistle. The European Food Safety Authority (EFSA) says it occurs naturally in onions, and to a lesser extent in foods such as beans, apples, grapes and tea.
More about Quercetin
LiverTox, the US government reference on drug-induced liver injury, says it is a regular part of a normal diet, found in high amounts in apples, berries, onions, broccoli and tomatoes, and in herbs such as ginkgo, St John's wort and milk thistle. The European Food Safety Authority (EFSA) says it occurs naturally in onions, and to a lesser extent in foods such as beans, apples, grapes and tea.
LiverTox says quercetin has been put forward as good for health in many ways: improving metabolic function, modulating inflammation, lowering cholesterol and improving athletic performance. It says the interest comes from studies of diets rich in foods containing quercetin, and from laboratory and animal studies, including of its antioxidant activity.
It is sold over the counter as a supplement on its own, according to LiverTox, and is often one ingredient in multi-ingredient products advertised for general health, weight loss, body building and energy. A 2023 review notes that the name strictly means the plain compound, without an attached sugar, but is often used for any quercetin-type molecule.
A 2016 review says that most quercetin eaten in food is not absorbed, and is broken down by gut bacteria instead. It adds that taking quercetin supplements for blood pressure means 10 to 60 times the average intake from food.
At a glance
Safety: known risks and 1 group who should avoid it or take extra care. See Safety ↓Claims made about Quercetin, and how strong the evidence is for each:
- Lowers blood pressureEvidence rating: Limited
- Helps people lose weightEvidence rating: Evidence against
- Improves endurance exercise performanceEvidence rating: Limited
- Eases muscle damage and soreness after hard exerciseEvidence rating: Limited
- Helps people with COVID-19 recoverEvidence rating: Limited
- Improves liver tests and blood fats in fatty liver diseaseEvidence rating: Limited
- Protects the body’s cells from oxidative damageEvidence rating: Insufficient
Each rating follows our published rules and the sources cited for it. We don’t add our own medical judgment. How we rate
Safety
Read this before the ratings below.
Risks
- LiverTox, the US government reference on drug-induced liver injury, states that quercetin “is well tolerated and generally reported as having no discernable adverse effects”. It says abdominal discomfort, nausea and headache have been reported in some studies, “but generally at low rates that are similar to those with placebo therapy”.
- LiverTox says quercetin supplements have not been linked to raised liver enzymes or to cases of clinically apparent liver injury, “although there have been few focused studies of its hepatic safety”. It rates quercetin an unlikely cause of clinically apparent liver injury (its likelihood score E).
- The NIH Office of Dietary Supplements (ODS) states that the exercise studies it describes, whose participants “took as much as 1,000 mg/day quercetin for up to 2 months”, found no side effects or safety concerns. It adds: “The safety of longer term use of that amount of quercetin or more has not been studied.”
- ODS states: “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.”
- The 2016 blood pressure review cited below says further trials are needed “to explore possible drug interactions between quercetin and antihypertensive drugs”, because quercetin is broken down by the cytochrome P450 enzyme system. It does not report any such interaction.
Who should avoid it or take extra care
- LiverTox reports that a review of the safety of quercetin supplements by the German Federal Institute for Risk Assessment concludes that there is “inadequate information on the safety of quercetin supplements in humans” and that patients “consult a physician prior to the use”.
Safety sources: Source [1]Source [2]Source [3]
What the evidence says
Each claim is rated on its own evidence. Ratings follow the scale on our methodology page.
Lowers blood pressure Evidence rating: Limited
People take it hoping it will bring their blood pressure down.
A 2016 review of seven small trials found falls of about 3 and 2.6 mm Hg, which were no longer statistically significant once one trial, in women with type 2 diabetes, was left out.
A 2016 systematic review pooled seven randomized, placebo-controlled trials with 587 participants, who took quercetin by mouth for 4 to 10 weeks. It found falls of about 3 mm Hg in systolic blood pressure (the top number) and 2.6 mm Hg in diastolic blood pressure (the bottom number). The reviewers call this effect “substantial”, given that most participants did not have high blood pressure.
Only one of the trials enrolled people with raised blood pressure; the others were in people without high blood pressure. When the reviewers left out one trial, in women with type 2 diabetes, neither fall was statistically significant.
The reviewers call the trials small and short. Their funnel plots suggested possible publication bias, though the falls were still present after their statistical adjustment for it. The review does not grade how sure it is (certainty).
LiverTox, the US government reference on drug-induced liver injury, summarizes this review as finding “a mild effect”. Its overview, last updated in 2020, says quercetin extracts “have not been shown to be effective in clinical trials for any medical condition”.
Sources: Source [1]Source [2]
Helps people lose weight Evidence rating: Evidence against
People take it hoping it will help them lose weight.
A 2019 review of nine short trials found no significant change in body weight, BMI or waist size; it rated that high certainty, while noting limits in the trials.
A 2019 systematic review pooled nine randomized, placebo-controlled trials with 525 adults, who took quercetin for 2 to 12 weeks. They included people who were overweight or obese, healthy adults, people with high blood pressure and women with polycystic ovary syndrome. It found no significant change in body weight, body mass index (BMI), waist size or waist-to-hip ratio.
The reviewers rate how sure they are (certainty) as high for weight, BMI and waist size, and moderate for waist-to-hip ratio, which only two trials measured. They also describe the nine trials as “of moderate quality”, note that “only three studies provided adequate random sequence generation”, and say the waist results “should be interpreted with caution”. On dose and duration they write: “These factors prevent us from being certain about the efficacy of quercetin as a weight-reducing agent.” They conclude that quercetin “is not recommended as a potential therapeutic strategy in weight loss”.
Five of the nine trials gave capsules of quercetin-rich onion peel extract; four gave quercetin capsules or tablets. The reviewers note that weight was not the main outcome of most trials, and that because the trials were short, longer-term effects are unknown.
LiverTox notes that quercetin is often an ingredient in multi-ingredient supplements advertised for weight loss. It summarizes this review as finding “no evidence for an effect on body weight or waist circumference”. This page rates the claim on the review's conclusion, for adults over trials of up to 12 weeks.
Sources: Source [1]Source [2]
Improves endurance exercise performance Evidence rating: Limited
People who run, cycle or train take it hoping it will boost their stamina.
The NIH Office of Dietary Supplements says numerous small, short trials found little to no effect on endurance performance or maximal oxygen uptake.
The NIH Office of Dietary Supplements (ODS) describes numerous small studies of quercetin as an aid to exercise, mostly in young adult men. They tested endurance and maximal oxygen uptake (VO2max) in running or cycling trials, with quercetin or a placebo taken for 1 to 8 weeks.
ODS says the effects “were inconsistent and varied by study”. They ranged from no benefit to “only a trivial or small improvement that might not be meaningful in real-world (in contrast to laboratory) exercise conditions”. ODS sums up the research as finding little to no effect on endurance performance or maximal oxygen uptake. It says larger trials are needed “before any recommendations can be made”.
Sources: Source [1]
Eases muscle damage and soreness after hard exercise Evidence rating: Limited
People who exercise hard take it hoping it will ease sore muscles and speed their recovery.
A 2023 review of 13 small studies, mostly in young men, found less soreness and a lower muscle-damage marker with quercetin, and its authors say the findings should be interpreted cautiously.
A 2023 systematic review included 13 small studies of healthy participants, mostly young men, from sedentary to well trained. It counts 249 participants, but its table lists two of the studies with identical details (20 trained male cyclists given quercetin and 20 a placebo), so some people may be counted twice.
Participants took quercetin or a placebo before hard exercise meant to cause muscle damage: one trial gave a single dose, the others gave it daily for a week or more beforehand. Pooled, the review found less muscle soreness, adding that “the results were not always significant” when single studies were removed. It also found lower levels of creatine kinase, a blood marker of muscle damage. It found no significant difference in IL-6, a marker of inflammation.
The reviewers had some concerns about bias in every trial: none described how participants were randomized or how the allocation was concealed. The soreness result came from four trials and the creatine kinase result from six, and both varied widely between trials. The review does not grade how sure it is (certainty).
The review reports some figures differently in different places. It gives the soreness result as 0 to 24 hours after exercise in its results, and as 24 to 48 hours in its discussion. Its discussion says eleven studies met its criteria, against 13 elsewhere.
The authors conclude that their findings “should be interpreted cautiously”, because few studies were included and some results were significant only when certain studies were removed. They say more evidence is needed in women and older adults.
Sources: Source [1]
Helps people with COVID-19 recover Evidence rating: Limited
People with COVID-19 take it hoping it will help them recover and keep them out of hospital.
A 2023 review found fewer hospital admissions and deaths with quercetin in three open-label trials, but rated the evidence low to very low certainty.
A 2023 systematic review pooled five randomized trials in people with COVID-19, in Pakistan, Ukraine and Iran, who took quercetin for one to four weeks. Its results for hospital admission, intensive care (ICU) admission and death rest on three of the trials. Pooled, all three were less common with quercetin, with risk ratios of 0.30, 0.27 and 0.18. For deaths, there were none with quercetin against seven without, and the confidence interval runs from 0.03 to 0.98. The review says all its trials were double-blinded. Each of the three trials describes itself as open-label, and each compared quercetin plus usual care with usual care alone, without a placebo.
Two of the trials, in outpatients in Pakistan, gave Quercetin Phytosome, a form of quercetin made by the company Indena; one paper describes it as quercetin “formulated with sunflower lecithin”. The papers state that some of their authors were Indena employees, and both thank Indena and Pharmextracta for supporting the study. The larger of them, in 152 outpatients, carries 81% of the weight of the hospital admission result. In that trial the usual-care group had more people with other illnesses, a difference its authors call significant. Among people without other illnesses, the differences in hospital admission, ICU admission and death were not statistically significant.
The third trial, in Iran, gave quercetin with the antiviral drugs remdesivir or favipiravir to people already in hospital with severe COVID-19. The review still includes it in the hospital admission result, and its entry there matches the trial's deaths (none with quercetin, three without), which the review also counts in the death result. The trial's authors call their death and ICU results “non-significant borderline”.
The review rates how sure it is (certainty) as low for admissions and deaths. It rates it very low for CRP, D-dimer and ferritin, blood markers of inflammation and clotting, which did not change significantly. It notes that the trials were small, gave quercetin in different formulations, and were mostly in Asian countries.
The review states its main result in two ways. Its abstract and results report the risks as 70%, 73% and 82% lower. A second summary in the abstract says the risks fell “by 30% and 27%”, and deaths “by 18%”. This page reports the risk ratios. The reviewers also cite another 2023 review that found quercetin “did not reduce the risk of mortality or promote recovery”, though it lowered hospital and ICU admission.
Improves liver tests and blood fats in fatty liver disease Evidence rating: Limited
People with fatty liver disease take it hoping it will improve their liver tests.
A 2025 review of nine small trials found lower liver enzymes and cholesterol with quercetin, rated very low certainty for the main liver enzymes and moderate to low for blood fats.
This claim is about blood tests in metabolic dysfunction-associated steatotic liver disease (MASLD), the new name for non-alcoholic fatty liver disease. A 2025 systematic review pooled nine randomized trials, reported in seven articles, with 540 participants. Four of the articles came from Ukraine, two from Iran and one from China. Quercetin was taken by mouth for 10 days to 12 weeks.
Pooled, the review found lower liver enzymes (ALT, AST and GGT), lower total and LDL cholesterol and triglycerides, and higher HDL cholesterol. It found no significant change in fasting blood sugar, BMI, body fat or kidney tests. The reviewers note that none of the studies assessed liver scarring (fibrosis) or other structural outcomes.
The reviewers rate how sure they are (certainty) as very low for ALT, AST and GGT, moderate for total, LDL and HDL cholesterol, and low for triglycerides. Their certainty table marks inconsistency as not serious for the cholesterol results, although their analyses report very high variation between trials for them.
One included trial gave quercetin together with ursodeoxycholic acid (UDCA), a bile acid treatment. The reviewers say this could have inflated the pooled liver enzyme results. They describe their findings as “preliminary” and as “hypothesis-generating evidence rather than definitive conclusions”.
Sources: Source [1]
Protects the body’s cells from oxidative damage Evidence rating: Insufficient
People take it as an antioxidant, hoping it will protect their cells from damage.
EFSA concluded in 2011 that a link between quercetin and protecting DNA, proteins and fats from oxidative damage has not been established.
The European Food Safety Authority (EFSA) assessed a proposed “antioxidant properties” claim for quercetin in 2011. It took the claim to mean protection of DNA, proteins and lipids (fats) from oxidative damage, which it says may be a beneficial physiological effect. It concluded that a cause and effect relationship “has not been established”.
EFSA explains that the only human study it was given that used a valid marker of oxidative damage to DNA showed no effect. That study compared a high-flavonol diet, which included onion cake and black tea, with a low-flavonol diet in 36 healthy people. EFSA adds that laboratory studies of quercetin's antioxidant capacity are not enough to predict an effect in people.
A 2023 review of exercise trials, described above under muscle damage, pooled markers of oxidative stress measured after hard exercise. It reports them as lower with quercetin, but the confidence interval it gives crosses zero, and the result “became nearly significant (p = 0.06)” after three named trials were left out. The sources differ in scope and method, so this page takes the lower rating.
Sources: Source [1]Source [2]
Which form the evidence used
Supplements are sold in several forms. This is what the sources on this page say about them — which form the research used, and any comparison those sources themselves made. Where they made none, this page does not rank the forms.
Quercetin capsules or tablets, What the sources supportDetails
The 2019 weight-loss review says four of its nine trials used quercetin capsules or tablets. The 2016 blood pressure review lists every one of its seven trials as giving quercetin by mouth. None of the cited reviews compared quercetin with enhanced-absorption versions. Source [1]Source [2]
Quercetin-rich onion peel extract, What the sources supportDetails
The 2019 weight-loss review says five of its nine trials gave capsules of quercetin-rich onion peel extract rather than quercetin on its own. Source [1]
Sources
- Effects of Quercetin on Blood Pressure: A Systematic Review and Meta-Analysis of Randomized Controlled TrialsJournal of the American Heart Association, 2016 · Meta-analysis · Primary source
- QuercetinLiverTox: Clinical and Research Information on Drug-Induced Liver Injury, National Institute of Diabetes and Digestive and Kidney Diseases, 2020 · Health authority summary · Primary source
- Clinical effectiveness of quercetin supplementation in the management of weight loss: a pooled analysis of randomized controlled trialsDiabetes, Metabolic Syndrome and Obesity: Targets and Therapy, 2019 · Meta-analysis · Primary source · Certainty: moderate
- Dietary Supplements for Exercise and Athletic Performance: Fact Sheet for Health ProfessionalsNIH Office of Dietary Supplements, 2024 · Health authority summary · Primary source
- Quercetin supplementation promotes recovery after exercise-induced muscle damage: a systematic review and meta-analysis of randomized controlled trialsBiology of Sport, 2023 · Meta-analysis · Primary source
- The effect of quercetin supplementation on clinical outcomes in COVID-19 patients: A systematic review and meta-analysisFood Science & Nutrition, 2023 · Meta-analysis · Primary source · Certainty: very low
- Possible Therapeutic Effects of Adjuvant Quercetin Supplementation Against Early-Stage COVID-19 Infection: A Prospective, Randomized, Controlled, and Open-Label StudyInternational Journal of General Medicine, 2021 · Randomized controlled trial · Supporting source
- Potential Clinical Benefits of Quercetin in the Early Stage of COVID-19: Results of a Second, Pilot, Randomized, Controlled and Open-Label Clinical TrialInternational Journal of General Medicine, 2021 · Randomized controlled trial · Supporting source
- Effects of Quercetin on Metabolic Dysfunction-Associated Steatotic Liver Disease: A Systematic Review and Meta-AnalysisFood Science & Nutrition, 2025 · Meta-analysis · Primary source · Certainty: very low
- Scientific Opinion on the substantiation of health claims related to quercetin and protection of DNA, proteins and lipids from oxidative damage (ID 1647), “cardiovascular system” (ID 1844), “mental state and performance” (ID 1845), and “liver, kidneys” (ID 1846) pursuant to Article 13(1) of Regulation (EC) No 1924/2006EFSA Panel on Dietetic Products, Nutrition and Allergies (EFSA Journal), 2011 · Health authority summary · Primary source
Page history
Show all 3 changes to this page
- — Published.
- — Revised after source and wording review: the COVID-19 claim now names the open-label design, the product used and the three trials behind its main result; caveats added to the weight-loss, blood pressure and muscle claims; safety notes reworded. No rating changed.
- — Drafted.