- 01A capsule is not an onion
Quercetin in food comes in small, sugar-bound, well-absorbed amounts. A 500 mg capsule of the pure form is about 20 times a typical diet's intake, and at that dose quercetin starts acting like a drug: it nudges blood pressure, uric acid and HDL, and it changes the levels of some medicines. Judge the capsule by its dose, not by the foods it comes from.
Quercetin is a natural plant pigment found in onions, apples, tea and many other foods, and sold as a supplement in doses roughly 20 times what a typical diet supplies 141. At those doses its best-supported effect is a small fall in systolic blood pressure, about 2 points, while pooled trials found no effect on cholesterol, blood sugar, inflammation or weight 3. Smaller trials point to lower uric acid and fewer colds after very hard training, but a 1,002-person trial found no effect on colds in ordinary adults 51011. Quercetin is usually well tolerated, but at capsule doses it changes how the body absorbs and clears certain medicines, which makes the medicine check the part that matters most 18.
What is quercetin?
Quercetin is a flavonol, a type of flavonoid (a large family of plant compounds that give fruit and vegetables much of their color). In food it is mostly bound to sugars as glycosides; in supplements it is mostly the free form, called the aglycone 114. That difference matters: in a Dutch study, people absorbed 52% of the quercetin glycosides from onions but only 24% of pure quercetin aglycone 14. The same research group estimated that the Dutch diet supplied about 23 mg a day of flavonols and flavones combined 14.
In the lab, quercetin acts as an antioxidant (a compound that neutralizes reactive molecules that damage cells) and blocks xanthine oxidoreductase, the enzyme that makes uric acid, which is why it was tested on uric acid 5. It also blocks P-glycoprotein, a pump that moves many drugs out of gut cells, which explains its effect on some medicines 8. Labels may say quercetin, quercetin dihydrate, or isoquercetin (a sugar-bound form).
Quercetin benefits: the evidence, graded
We grade each use by the quality of the human research. Strong means several good randomized trials or a meta-analysis agree; Moderate means several randomized trials, mostly positive but small or short; Limited means few or small trials, or mixed results; Early means lab, animal or a single pilot study; Not supported means good trials found no benefit. Our supplements explainer says more about grading.
| Use | What the research found | Evidence | Source |
|---|---|---|---|
| Systolic blood pressure (top number) | Pooled trials: about 1.9 mmHg lower than placebo; certainty very low to moderate, results inconsistent. | Moderate | 34 |
| Fasting insulin | Pooled trials: a small drop. | Limited | 3 |
| Uric acid | One 4-week crossover trial of 22 men with high-normal uric acid: down 26.5 micromoles per liter on 500 mg a day. | Limited | 5 |
| Colds after intense training | 40 trained cyclists: 1 of 20 on quercetin got a cold after a hard 3-day block versus 9 of 20 on placebo. | Limited | 10 |
| Colds in the general population | 1,002 adults for 12 weeks: no difference in cold rates or symptoms. | Not supported | 11 |
| Diastolic pressure, cholesterol, blood sugar, CRP, weight | Pooled trials found no effect. | Not supported | 3 |
| Exercise endurance | Seven studies: about 0.7% better endurance, judged likely trivial. | Not supported | 12 |
| "Senolytic" (clearing aging cells) | One 12-person pilot with no control group, using quercetin together with the cancer drug dasatinib. | Early | 16 |
| Allergies ("natural antihistamine") | We found no good human trials of quercetin alone. | Early | None found |
Quercetin and blood pressure
This is quercetin's best-supported result, though individual trials varied widely. A 2023 umbrella review (a review of meta-analyses) covering 18 trials plus 5 newer ones found quercetin lowered systolic blood pressure by 1.9 mmHg on average, with no effect on diastolic pressure (the bottom number) 3. One of the better individual trials gave 93 overweight adults with metabolic-syndrome traits 150 mg a day for 6 weeks: systolic pressure fell 2.6 mmHg overall and 2.9 mmHg in those with high blood pressure 4. A 2-point drop is real but small; diet, activity, and where needed medicine, move blood pressure far more. Quercetin is not a treatment for high blood pressure, which is diagnosed and managed by a clinician, and never a swap for a prescribed blood pressure medicine.
The same trial found something less welcome: HDL cholesterol fell on quercetin, while oxidized LDL, a damaged form of LDL, also fell 4. Total cholesterol, triglycerides and CRP did not change 4. Our lipid panel guide and cholesterol ratio calculator explain why HDL alone is a weak guide to heart risk.
Does quercetin lower uric acid?
In one small trial, yes. Twenty-two healthy men aged 19 to 60, whose uric acid was in the higher but still normal range (about 339 micromoles per liter, or 5.7 mg/dL), took 500 mg of quercetin a day for 4 weeks in a placebo-controlled crossover design. Uric acid fell by 26.5 micromoles per liter (about 0.45 mg/dL) without changes in blood pressure or fasting glucose 5. A separate 2-week trial at 50 to 150 mg a day found no change in uric acid, so dose may matter 15. This was not a trial in people with gout. A high uric acid result, or gout symptoms, goes to a clinician first: gout has effective prescription treatments, and quercetin is not one of them.
Quercetin, colds and exercise
The immune story is narrower than the marketing. In 40 trained cyclists given 1,000 mg a day around a punishing 3-day cycling block, 1 of 20 on quercetin caught an upper respiratory infection over the next 2 weeks, versus 9 of 20 on placebo, though measures of immune function did not differ 10. When the same group tested 500 or 1,000 mg a day in 1,002 ordinary adults for 12 weeks, there was no difference in cold rates or symptoms overall; only fit adults over 40 on the higher dose had fewer sick days 11. For performance, seven studies found endurance improved by 0.74%, which the authors judged likely trivial 12.
Published adequate scientific data for safety assessment in regard to the long-term use (>12 weeks) of high supplemental quercetin doses (≥1000 mg) are currently not available.
How much quercetin do studies use?
These are amounts studies used, not a dose for you. Quercetin has no Recommended Dietary Allowance and no NIH upper limit. Supplements commonly provide up to 1,000 mg a day, far above usual diets, and there are no adequate safety data for 1,000 mg or more taken for longer than 12 weeks 1.
| Use or study | Amount studied | Form | How long | Source |
|---|---|---|---|---|
| Blood pressure | 150 mg a day | Quercetin | 6 weeks | 4 |
| Uric acid | 500 mg a day | Quercetin tablet | 4 weeks | 5 |
| Colds after training | 1,000 mg a day | Quercetin | About 5 weeks | 10 |
| Colds in the community | 500 or 1,000 mg a day | Quercetin | 12 weeks | 11 |
| Exercise performance (pooled) | About 1,000 mg a day | Quercetin | Days to weeks | 12 |
| Platelet study | 150 or 300 mg once | Quercetin glucoside | Single dose | 6 |
| Fexofenadine interaction | 500 mg three times a day | Quercetin | 7 days | 8 |
| Senolytic pilot | 1,250 mg with dasatinib, 2 days every 2 weeks | Quercetin plus a cancer drug | 12 weeks | 16 |
| Typical Dutch diet | About 23 mg a day (flavonols and flavones) | Food | Daily | 14 |
One LifeFrom capsule holds 500 mg of quercetin, the same amount used in the uric acid trial and the lower arm of the community cold trial, and more than three times the 150 mg used in the blood pressure trial 4511.
When and how to take quercetin
How quercetin was taken in studies
How long does quercetin take to work? Blood levels climbed in a dose-dependent way over 2 weeks 15; the uric acid change was measured at 2 and 4 weeks, and the blood pressure change after 6 weeks 45. What is quercetin's half-life? About 3.5 hours on average in one study of 500 mg taken three times a day, but the body sends quercetin back to the gut in bile and reabsorbs it, so blood levels rise and fall more than once 13. Platelet effects appeared within 30 minutes of a single dose of a well-absorbed form 6.
Quercetin in food vs a quercetin capsule
Onions and tea vs a 500 mg capsule
Quercetin side effects
Across many human trials, side effects of supplemental quercetin have rarely been reported, and those reported were mild 1. In the 6-week blood pressure trial, blood tests of liver and kidney function, blood counts and electrolytes showed no adverse changes 4. LiverTox says quercetin is well tolerated and has not been linked to liver enzyme rises or clinically apparent liver injury 2. The open questions come from animal studies and long-term high doses 1.
| What is known | What is uncertain or needs prompt care |
|---|---|
| Side effects in trials were rare and mild 1 | No adequate safety data for 1,000 mg or more taken longer than 12 weeks 1 |
| No liver-injury signal in LiverTox 2 | Animal studies suggest quercetin could worsen damage in an already injured kidney 1 |
| No adverse blood-test changes in a 6-week trial 4 | Animal studies raised a concern about tumor promotion in estrogen-dependent cancers 1 |
| HDL cholesterol fell in one trial 4 | On a blood thinner: unusual bruising, black stools or bleeding that will not stop needs same-day care 7 |
Who should avoid quercetin or ask first
- Pregnancy and breastfeeding: no adequate safety studies of quercetin supplements; the LifeFrom label says to consult a healthcare professional first. Food sources are a different matter.
- Children: the label says adults only.
- Kidney disease: animal studies suggest quercetin may worsen existing kidney damage; ask your kidney care team 1. Our kidney function guide explains creatinine and eGFR.
- Estrogen-sensitive cancer, now or in the past: ask your oncology team, because of animal findings on tumor growth 1.
- Blood thinners, antiplatelets, bleeding disorders or surgery coming up: quercetin reduced platelet clumping in people 67.
- Digoxin, cyclosporine, fexofenadine or other regular medicines: see the interactions below 189.
Quercetin interactions
| Medicine | What can happen | Why | What to do |
|---|---|---|---|
| Warfarin | INR rose from 2.5 to 7.5 in a 79-year-old man a few days after he started 250 mg of quercetin with vitamin C daily; it fell back after stopping | Not fully known; judged a probable reaction, though he also took amiodarone 7 | Talk to the prescriber first; ask whether your INR should be rechecked |
| Antiplatelets and other anticoagulants (aspirin, clopidogrel, apixaban) | Possible added bleeding effect | 150 to 300 mg of quercetin glucoside reduced platelet clumping within 30 minutes 6 | Ask the prescriber; mention it before surgery |
| Fexofenadine (allergy) | Blood levels 55% higher | Quercetin blocks the P-glycoprotein pump 8 | Ask a pharmacist; the dose may act stronger |
| Digoxin (heart) | Sharply higher levels; two of three pigs died at a high dose | P-glycoprotein blocked; animal study only 9 | Avoid together unless the prescriber agrees |
| Cyclosporine, tacrolimus and other P-glycoprotein drugs | Possible higher levels | These drugs are moved by P-glycoprotein, which quercetin blocks; short-term studies found altered levels of certain drugs 18 | Ask the transplant or prescribing team first |
| Blood pressure medicines | Systolic pressure may run about 2 points lower | Pooled trial effect 3 | Mention it to the prescriber |
| Uric acid and lipid tests | Uric acid and HDL may read lower | Trial effects 45 | Tell whoever reads your results that you take quercetin |
Supplements to pair or keep apart
| Supplement | Together or apart | Why |
|---|---|---|
| Resveratrol | Together in two LifeFrom packs; with care on blood thinners | Another polyphenol; both may affect platelets |
| Turmeric with piperine | Together in the Microbiome pack; with care on blood thinners | Curcumin is linked to bleeding risk, and piperine may raise levels of compounds taken with it |
| Vitamin C | Together | Shares the Antioxidants pack; the warfarin case product combined the two 7 |
| NAC | Together | No known interaction; shares the Antioxidants pack |
| Berberine | With care if you take regular medicines | Both change how some drugs are handled |
| Bromelain | No combined trials found | Often sold with quercetin; the pairing is popular but we found no good human trials of it |
Blood tests worth knowing about
No routine test measures quercetin, but it can move a few results, and kidney and clotting checks matter for some people. Ask your clinician whether any of these make sense for you.
| Marker | Why it matters with quercetin | When it is usually checked |
|---|---|---|
| Uric acid | Fell about 8% on 500 mg a day in one trial 5 | With gout symptoms or kidney stones; a high result goes to a clinician first |
| HDL cholesterol | Fell in a 6-week trial 4 | On a lipid panel |
| Oxidized LDL | Fell in the same trial 4 | Specialty heart panels |
| Fasting insulin | A small drop in pooled trials 3 | Metabolic and insulin-resistance testing |
| INR | Rose sharply in one warfarin case 7 | Regularly on warfarin; see our clotting tests guide |
| Creatinine and eGFR | Kidney checks, given the animal kidney findings 1 | Routine panels; see the eGFR calculator |
Conditions and goals quercetin comes up around
People look at quercetin for blood pressure, gout or high uric acid, high cholesterol, and immunity. Each is diagnosed and managed by a clinician, quercetin is not a treatment for any of them, and it is never a swap for a prescribed medicine. Anyone with chronic kidney disease should ask their kidney care team before starting, because of the animal kidney findings.
Quercetin in the LifeFrom pouch
| In the LifeFrom pouch | |
|---|---|
| Product | Quercetin |
| What one serving holds | 1 capsule: Quercetin 500 mg |
| Form | Capsule, vegan (hypromellose vegetable capsule) |
| How it is packed | One serving in each of your 30 daily pouches, with up to 8 supplements per pouch |
| Price | $10.80 a month, plus the fixed $28.50 a month packing, handling and US delivery line for the whole pouch, not per supplement. Prices as of November 2026; the shop shows the current price. |
| Curated packs that include it | Microbiome; Antioxidants |
The 500 mg serving matches the uric acid trial and is above the 150 mg used in the blood pressure trial 45. Everything in a pouch is taken at once. The Microbiome pack puts quercetin with Turmeric (which carries 5 mg of piperine, an absorption booster), Berberine 300 and Resveratrol, and both packs pair it with Resveratrol; quercetin, curcumin and resveratrol each have platelet or bleeding signals, so anyone on a blood thinner should show the whole pack list to their prescriber. See the shop and its packs.
This guide is general education, not medical advice. Supplements are not approved by the FDA for safety or effectiveness before they are sold. The clinician or pharmacist who knows your history and medicines is the right person to decide whether quercetin makes sense for you; see our medical disclaimer.
Citations
- Andres S, et al. Safety aspects of the use of quercetin as a dietary supplement. Mol Nutr Food Res. 2018. German Federal Institute for Risk Assessment.
- LiverTox: Clinical and Research Information on Drug-Induced Liver Injury. Quercetin. National Institute of Diabetes and Digestive and Kidney Diseases (NCBI Bookshelf).
- Arabi SM, et al. The effects of quercetin supplementation on cardiometabolic outcomes: an umbrella review of meta-analyses of randomized controlled trials. Phytother Res. 2023.
- Egert S, et al. Quercetin reduces systolic blood pressure and plasma oxidised low-density lipoprotein concentrations in overweight subjects with a high-cardiovascular disease risk phenotype. Br J Nutr. 2009.
- Shi Y, Williamson G. Quercetin lowers plasma uric acid in pre-hyperuricaemic males: a randomised, double-blinded, placebo-controlled, cross-over trial. Br J Nutr. 2016.
- Hubbard GP, et al. Ingestion of quercetin inhibits platelet aggregation and essential components of the collagen-stimulated platelet activation pathway in humans. J Thromb Haemost. 2004.
- Patel R, Stine A, Zitko K. Enhanced anticoagulant effect of warfarin when co-administered with quercetin. J Pharm Technol. 2022.
- Kim KA, Park PW, Park JY. Short-term effect of quercetin on the pharmacokinetics of fexofenadine, a substrate of P-glycoprotein, in healthy volunteers. Eur J Clin Pharmacol. 2009.
- Wang YH, et al. Lethal quercetin-digoxin interaction in pigs. Life Sci. 2004.
- Nieman DC, et al. Quercetin reduces illness but not immune perturbations after intensive exercise. Med Sci Sports Exerc. 2007.
- Heinz SA, et al. Quercetin supplementation and upper respiratory tract infection: a randomized community clinical trial. Pharmacol Res. 2010.
- Pelletier DM, Lacerte G, Goulet ED. Effects of quercetin supplementation on endurance performance and maximal oxygen consumption: a meta-analysis. Int J Sport Nutr Exerc Metab. 2013.
- Moon YJ, et al. Quercetin pharmacokinetics in humans. Biopharm Drug Dispos. 2008.
- Hollman PC, Katan MB. Dietary flavonoids: intake, health effects and bioavailability. Food Chem Toxicol. 1999.
- Egert S, et al. Daily quercetin supplementation dose-dependently increases plasma quercetin concentrations in healthy humans. J Nutr. 2008.
- Millar CL, et al. A pilot study of senolytics to improve cognition and mobility in older adults at risk for Alzheimer's disease. EBioMedicine. 2025.
Educational context only, not medical advice or a diagnosis. Always discuss your results with a clinician.
