A plant flavonol found in onions, apples and tea. Two reviews found systolic blood pressure about 2 to 3 mmHg lower than with placebo. For training the evidence is early and mixed: one review found less soreness and two found endurance and VO2max about 1 to 2% better, but the largest trial, of ultramarathon runners, and the newest, of trained cyclists, found no difference from placebo.
Quercetin is a flavonol, one of the flavonoids plants make, and one of those most eaten, in apples, onions, berries, leafy greens and tea. Strictly the name means the aglycone, the molecule without an attached sugar, though it is often used for any quercetin-type molecule; the recovery trials gave 1,000 mg a day in all but one.
My take
Core
Situational
Trying
Researching
Not taking
B-tier. Not foundational, but a good add-on once the rest of your stack is set.
What to buyRead the label for the form and the milligrams: plain quercetin, the aglycone, often as quercetin dihydrate, or an enhanced form such as a phytosome or isoquercetin. Mine reads quercetin, as quercetin dihydrate, from Sophora japonica flower bud, 1,000 mg.
How to take itI take 1,000 mg every morning with breakfast; in one study a high-fat breakfast raised the quercetin reaching the blood by about a third over a fat-free one. I started it for my lungs and breathing: diet studies link eating more flavonoids to better lung function and less COPD, but they observe diets rather than test a supplement, and no trial has yet shown a quercetin supplement does that.
What to expectSmall effects, if any. In the endurance trials, a median of 11 days at 1,000 mg a day in one review, VO2max and performance rose about 1 to 2% more than on placebo, and the performance gain not in trained people; in the recovery trials, taken in all but one for more than a week and up to 12 weeks before a hard session, in the other as a single dose, soreness and muscle damage were a little lower in the day or two after.
What the studies show
1 Strong4 Preliminary
Each segment is one studyBetterNo changeWorse
Strong: at least one pooled review or three randomised trials among the counted studies, and at least three in four of them better. Preliminary: everything else. Better is green in a Strong finding and ochre in a Preliminary one.
Better means a statistically significant change in the claimed direction at a normal dose. Each study counts once: a pooled review speaks for the trials inside it.
1of 2 studies betterof 2
Recovery after hard exercise
249 people, Rojano-Ortega 2023 · less soreness and muscle damage, in small trials of mostly young men
1 of 2 studies better
In young people, mostly men and sedentary to well trained, a review of 13 small trials, 10 to 20 people a group, found less soreness and less creatine kinase, a marker of muscle damage, in the day or two after hard exercise at 1,000 mg a day, and four of its five trials that measured functional variables found it better after exercise or through recovery; it rates every trial at some risk of bias. In the largest trial, of 63 ultramarathon runners, 1,000 mg a day for three weeks left creatine kinase drawn just after a 160-km race no lower than with placebo.
Preliminary
Recovery
What these 2 studies found. Pooled reviews: 1 better. Trials: 1 no change.
In sedentary to well-trained young people, mostly men, soreness 0 to 24 hours after hard exercise (SMD −1.33, 4 of its 13 trials) and creatine kinase 24 to 48 hours after (SMD −1.15, 6 trials) lower than placebo, and oxidative stress lower (SMD −0.92); IL-6 did not differ. Four of its five trials that measured functional variables found it better after exercise or through recovery; it rates every trial at some risk of bias.
In 63 ultramarathon runners (39 finished), 1,000 mg a day for three weeks before the 160-km Western States Endurance Run left the rise in creatine kinase after the race (21,575 against 19,455 U/L), CRP and nine plasma cytokines no different from placebo.
Nieman 2007 Journal of Interferon & Cytokine Research
Randomised trial
63 ultramarathon runners
1,000 mg quercetin a day · 3 weeks
Found with a PubMed search: quercetin in the title with muscle damage, soreness, DOMS, recovery, eccentric exercise, creatine kinase or muscle function in the title or abstract, or quercetin in the title or abstract with muscle damage, soreness, recovery, eccentric, muscle function, strength loss or muscle injury in the title, reviews and trials, human studies. 23 results on 17 Oct 2026.
2of 5 studies betterof 5
Endurance and VO2max, a small gain
288 people, Pelletier 2013 · endurance up 0.74% and VO2max 1.94%, the endurance gain only in untrained people
2 of 5 studies better
In healthy adults, two early reviews found endurance and VO2max a little better with quercetin than with placebo, about 1 to 2%, an effect each judges trivial or small, and the newer found the endurance gain only in untrained people. A review of supplements in military personnel found its one quercetin trial, in 16 soldiers, gave no gain, and in the largest trial, of 63 ultramarathon runners, and a newer one of 26 trained cyclists, race and time-trial times did not differ from placebo at 1,000 mg a day.
Preliminary
Endurance
What these 5 studies found. Pooled reviews: 2 better, 1 no change. Trials: 2 no change.
In active-duty military personnel, its one quercetin trial (16 of its 2,772), in soldiers taking 1,000 mg a day for about a week, did not improve VO2peak, a cycling time trial or perceived exertion; it finds the evidence does not support quercetin for performance.
In healthy adults, endurance performance 0.74% better than placebo (10 estimates) and VO2max 1.94% better (4 estimates); the performance gain was significant in untrained people only (0.83%, against 0.09% in trained, p = 0.92), and it judges both likely trivial and quercetin unlikely to prove ergogenic.
Pelletier 2013 International Journal of Sport Nutrition and Exercise Metabolism
In healthy adults across its 11 studies, VO2max and endurance performance together better than placebo (ES 0.15), an effect between trivial and small, about 2%, not linked to fitness or to the plasma quercetin reached, at a median 1,000 mg a day for 11 days.
Kressler 2011 Medicine and Science in Sports and Exercise
In 63 ultramarathon runners (39 finished), 1,000 mg a day for three weeks before the 160-km Western States Endurance Run left race times (26.4 against 27.5 hours) and perceived exertion no different from placebo.
In its quercetin and placebo arms (26 of 50 trained cyclists), 500 mg of quercetin dihydrate twice a day for 28 days left 20-km time-trial time and power no different from placebo; VO2 during the time trial rose from each group’s starting level in the quercetin group only.
Kurtz 2024 Journal of the International Society of Sports Nutrition
Randomised trial
50 trained cyclists
500 mg quercetin dihydrate twice a day · 28 days
Found with a PubMed search: quercetin in the title with endurance, aerobic, VO2max, VO2peak, maximal oxygen, oxygen uptake, time trial, time to exhaustion or performance in the title or abstract, or quercetin in the title or abstract with endurance, aerobic, VO2max, performance, exercise, ergogenic, athletes, cycling, running or fitness in the title, reviews and trials, human studies. 56 results on 17 Oct 2026.
2of 2 studies betterof 2
Blood pressure
841 people, Popiolek-Kalisz 2022 · systolic pressure about 2 mmHg lower, in people with normal blood pressure too
2 of 2 studies better
In adults, healthy or with raised blood pressure or metabolic risk, two reviews found systolic pressure about 2 to 3 mmHg lower than with placebo, the older finding the drop at 500 mg a day or more and not below, though the doses did not differ significantly from each other, the newer in people with normal blood pressure too, while diastolic pressure fell in the older review and in the newer in people with raised blood pressure; an umbrella review that re-pools the reviews found systolic pressure lower and diastolic no different. In the largest trial, of 93 overweight adults with metabolic syndrome traits, 150 mg a day for six weeks lowered systolic pressure by 2.6 mmHg in contrast to placebo.
Strong
Heart
What these 3 studies found. The ring counts 2 of them: the other is a trial pooled in Serban 2016, counted through it. Pooled reviews: 2 better. Pooled in Serban 2016: 1 better.
In adults with normal or raised blood pressure, systolic pressure 2.38 mmHg lower than placebo, and 1.82 lower in its normotensive subgroup; diastolic pressure was significantly lower in its (pre)hypertensive subgroup (3.14 mmHg).
Popiolek-Kalisz 2022 Current Problems in Cardiology
In adults, healthy or with raised blood pressure or metabolic risk, systolic pressure 3.04 mmHg and diastolic 2.63 lower than placebo, at 100 to 1,000 mg a day for 4 to 10 weeks; both fell at 500 mg a day or more (systolic 4.45 lower) and not below, though the doses did not differ significantly from each other.
Serban 2016 Journal of the American Heart Association
In 93 overweight and obese adults aged 25 to 65 with metabolic syndrome traits, 150 mg of quercetin a day for six weeks lowered systolic pressure by 2.6 mmHg, in contrast to placebo, by 2.9 in those with high blood pressure and 3.7 in those aged 25 to 50; diastolic pressure is not reported in the abstract.
Egert 2009 British Journal of Nutrition
Randomised crossover trial
93 overweight and obese adults with metabolic syndrome traits
150 mg quercetin a day · 6 weeks
Pooled in Serban 2016
Found with a PubMed search: quercetin in the title with blood pressure, hypertension, hypertensive, systolic or diastolic in the title or abstract, or quercetin in the title or abstract with blood pressure, hypertension, hypertensive, cardiometabolic, cardiovascular or metabolic syndrome in the title, reviews and trials, human studies. 48 results on 17 Oct 2026.
2of 3 studies betterof 3
Strength and muscle with training
54 people, Otsuka 2022 · no gain in muscle or strength over training alone, in adults aged 50 to 74
2 of 3 studies better
All three trials gave an enhanced form with training, not plain quercetin: in the largest, of 54 adults aged 50 to 74 on 24 weeks of light resistance training, 200 or 500 mg a day of quercetin glycosides added no muscle or strength over placebo, while in a trial of 30 adults aged 65 to 82, 200 mg a day raised knee-extension strength by 15% over six weeks of training, against 5% on placebo. In 39 college American-football players in team training, 42 mg a day of EMIQ, an enzymatically modified isoquercitrin, in whey protein for four months raised leg muscle mass more than whey alone, though lean mass overall did not differ and strength was not measured.
Preliminary
Strength
What these 3 studies found. Trials: 2 better, 1 no change.
In 54 previously inactive adults aged 50 to 74 (48 analysed), 200 or 500 mg of quercetin glycosides a day with the same machine resistance training at 40% of 1-RM three days a week for 24 weeks left thigh muscle cross-sectional area, its main outcome, lean mass and 1-RM strength no different from placebo; muscle stiffness fell more in both quercetin groups.
Otsuka 2022 Frontiers in Nutrition
Randomised trial
54 previously inactive adults aged 50 to 74
200 or 500 mg quercetin glycosides a day · 24 weeks
In 39 male college American-football players in their team training, 42 mg of EMIQ (enzymatically modified isoquercitrin) in 20 g of whey protein six days a week for four months raised lower-limb muscle mass (+931 against +256 g, p = 0.021) and lower-limb fat-free mass (+950 against +324 g, p = 0.031) more than whey alone; lean body mass, body mass and fat mass did not differ, and strength was not measured.
Omi 2019 Journal of the International Society of Sports Nutrition
Randomised trial
39 male college American-football players
42 mg EMIQ a day in 20 g whey protein, six days a week · 4 months
In 30 healthy adults aged 65 to 82 (26 finished), 200 mg of quercetin glycosides a day with the same isometric knee-extension training three times a week for six weeks raised knee-extension strength, its main outcome, by 15% against 5% on placebo (p < 0.001); muscle mass, muscle thickness and the Timed Up and Go and chair-stand tests did not differ.
Nishikawa 2025 European Journal of Nutrition
Randomised trial
30 healthy adults aged 65 to 82
200 mg quercetin glycosides a day · 6 weeks
Found with a PubMed search: quercetin, isoquercetin, isoquercitrin or EMIQ in the title with strength, resistance training or exercise, muscle mass, lean mass, muscle function, sarcopenia, motor units or one-repetition maximum in the title or abstract, or any of them in the title or abstract with strength, muscle, training, sarcopenia, motor units, athletes or physical in the title, reviews and trials, human studies. 28 results on 17 Oct 2026.
1of 1 study betterof 1
Altitude sickness and oxygen saturation at altitude
110 people, Sagi 2026 · mountain sickness in 2% against 25% on placebo, in healthy lowland men
1 of 1 study better
In one trial of 110 healthy lowland men aged 20 to 40 climbing to 3,048 m and then 3,750 m, 500 mg of quercetin a day in a food bar, started two days before the ascent and taken for 15 days, cut acute mountain sickness to 2% of the men against 25% on placebo and kept oxygen saturation higher, 94% against 90%. Blood pressure, which it also measured, was lower at altitude with quercetin, systolic by 8 mmHg and diastolic by 4, while body weight and fat did not differ.
In 110 healthy lowland men aged 20 to 40 ascending from 440 m to 3,048 m for six days and then 3,750 m, 500 mg of quercetin a day in a food bar for 15 days, from two days before the ascent, lowered the incidence and severity of acute mountain sickness against a placebo bar (2% against 25% by the end) and kept arterial oxygen saturation higher (94.0 against 90.0%, p < 0.001); systolic pressure was 8 mmHg and diastolic 4 lower, and body weight and fat did not differ.
Sagi 2026 European Journal of Nutrition
Randomised trial
110 healthy lowland men aged 20 to 40 at high altitude
500 mg quercetin a day in a food bar · 15 days
Found with a PubMed search: quercetin in the title with altitude, hypoxia, mountain sickness, oxygen saturation or SpO2 in the title or abstract, or quercetin in the title or abstract with altitude, hypoxia, mountain sickness, oxygen saturation or mountains in the title, reviews and trials, human studies. 4 results on 17 Oct 2026.
Dose
Thiago takes 1,000 mg a day, the top of the normal range: supplements are sold at up to 1,000 mg a day, and the recovery and endurance trials nearly all gave 1,000 mg, the blood-pressure trials in one review 100 to 1,000 mg, the drop seen at 500 mg or more, and the altitude trial 500 mg; the strength trials gave enhanced forms at 42 to 500 mg. A 2018 safety review found no adequate data on the long-term use, over 12 weeks, of 1,000 mg a day or more.
Daily500 to 1,000 mg, most trials’ doses of plain quercetin
A harm to the kidney that is unproven by mouth, the medicines whose blood levels it changes, and pregnancy.
UnprovenKidney harm
In a phase I trial in people with cancer, quercetin given into a vein harmed the kidneys in 3 of 14 patients at 945 mg/m² of body surface and limited the dose at 1,700 mg/m². By mouth, a 2018 safety review found side effects rarely reported and mild in human studies, and animal studies suggesting it may add to harm in a kidney already damaged.
Cyclosporine or another transplant drug, fexofenadine or another drug carried by P-glycoprotein, diclofenac or another drug cleared by the liver enzyme CYP2C9, chlorzoxazone or another drug cleared by CYP2E1, or a statin. In healthy volunteers, 500 mg of quercetin one to three times a day for one to two weeks raised blood levels of fexofenadine by 55%, of diclofenac and of chlorzoxazone, a muscle relaxant cleared by CYP2E1, beyond the limits of no effect, and of pravastatin by 24%. Quercetin changed exposure to cyclosporine, a drug with a narrow safe range, in opposite directions: up 18 to 47% in a study of healthy men, as a later paper reports it, and down 43% in rats.
Pregnant or breastfeeding. A 2022 safety review of Sophora japonica flower bud, sold as a source of quercetin, found no data on its use in pregnancy or breastfeeding and advises women then to ask a healthcare professional first.
Plain quercetin, the aglycone, as its dihydrate, and Thiago’s form.
This page
Quercetin Phytosome
Quercetin in a food-grade lecithin formulation. In 12 healthy volunteers a single 500 mg dose reached peak blood levels about 20 times those of 500 mg of unformulated quercetin.
Isoquercetin is one of quercetin’s glycosides, quercetin with a sugar attached. EMIQ, enzymatically modified isoquercitrin, is reported to be 17 times as bioavailable as the aglycone; in 25 adults at risk of heart disease one dose raised quercetin metabolites in the blood above placebo.
Quercetin combined in one product with vitamin C or with bromelain. In 16 healthy adults given 1,095 mg of the aglycone with a meal, absorption varied widely between people and was higher the lower the vitamin C already in their blood, not vitamin C taken with it.
Quercetin is a flavonol that acts as an antioxidant and against inflammation in the lab, but little of it is absorbed, by amounts that vary widely between people, and in healthy people two weeks of it at 50 to 150 mg a day left antioxidant status unchanged.
Flavonolone of the flavonoids
Plants make flavonoids, and quercetin, one of the flavonols among them, is one of those most eaten, in apples, onions, capers, berries and tea. Strictly the name means the aglycone, the molecule without an attached sugar.
ROSfree radicals, in the lab
Like other flavonoids it scavenges free radicals, among them reactive oxygen species (ROS), the free radicals derived from oxygen, and it has marked anti-inflammatory and antioxidant activity, effects shown mostly in preclinical studies.
37–96%variation between people
It dissolves poorly and is poorly absorbed by mouth. In 16 healthy adults given 1,095 mg of the aglycone with a meal, blood levels of quercetin and its metabolites varied widely between people, with coefficients of variation of 37 to 96%.
570%more in blood at 150 mg
In 35 healthy volunteers, 50 to 150 mg a day for two weeks raised blood quercetin from where it began, more with each dose, by up to 570% at 150 mg, but did not change antioxidant status, oxidised LDL or TNF-α, a marker of inflammation.