Awaiting clinical review. This entry is sourced but has not yet been signed off by a pharmacist or clinician.

Plant flavonoid (isolated compound)

Quercetin

Quercetin supplements lower blood pressure by a small amount in pooled trials (about 2 mmHg systolic), and may reduce muscle soreness after hard exercise. The evidence for hay fever and for immune protection in athletes is much weaker: the allergy data on quercetin itself are mostly from animals. It seems well tolerated in the short term, but a safety review found no data on long-term high doses and reported interactions that alter how some drugs are absorbed.

Written by

Healthy and Herbal editorial team

Updated

29 September 2026

Yellow capsules beside red onions and apples

At a glance

Last reviewed 29 September 2026

Evidence

Moderate

Best for

Small blood pressure drop

Typical form & use

Capsule, about 1,000 mg daily

Onset

4+ weeks

Safety

Can change how some medicines are absorbed. No interactions in our data.

Check with your medications →

What it's used for

Evidence is rated per use. The same ingredient can be strong for one thing and traditional for another.

Use	Evidence	What the research shows
Lowering blood pressure	Moderate	A 2022 meta-analysis of 10 randomised trials (841 people) found systolic pressure fell by 2.38 mmHg (95% CI 0.96 to 3.80) overall, and diastolic pressure by 3.14 mmHg in people with raised or borderline pressure. The effect is small, and it is unclear how much it matters for health outcomes.¹
Muscle soreness after hard exercise	Moderate	A 2023 meta-analysis of 13 studies (249 people) found quercetin reduced soreness, creatine kinase and oxidative stress markers after intense exercise, but did not change IL-6. All included studies had some risk-of-bias concerns, and nearly all used 1,000 mg a day in young men.²
Endurance performance	Limited	Two meta-analyses found statistically significant but trivial to small gains: about 2% in one, and 0.74% in endurance power output in the other, which its authors judged unlikely to matter. A 2021 systematic review of flavonoids found 25% of quercetin studies reported better performance.^3,4,7
Hay fever and allergic rhinitis	Traditional	The only quercetin-specific synthesis we found pooled animal studies, where it lowered IgE and histamine. In people, a 2025 meta-analysis of 13 trials (823 participants) found polyphenols as a group reduced nasal symptoms, but certainty was low to very low, quality of life did not improve and it did not test quercetin alone.^5,6
Immune protection in athletes	Traditional	A 2021 systematic review of flavonoids and exercise found few studies measured immune outcomes, and the two that found benefit used anthocyanin supplements, not quercetin. We did not find a systematic review showing quercetin prevents infections.⁷

How much

Ranges below are what studies used and what supplements commonly contain. They are not a recommendation for you. Start at the low end.

Studied dose

About 1,000 mg daily^2,3

Nearly all the exercise trials used 1,000 mg a day, with median treatment of 11 days in the endurance trials and up to 12 weeks for recovery.

Blood pressure trials

Dose not extracted¹

We only read the abstract of the blood pressure meta-analysis, which does not give doses. Check the full paper before quoting a dose for this use.

Long-term use

Unknown beyond 12 weeks⁸

A safety review found no adequate data on long-term use (over 12 weeks) of high doses (1,000 mg or more).

Timing · No source we read gave advice on time of day.With food? · No source we read gave food guidance. Supplements are often sold with bromelain or vitamin C to aid absorption, but we found no source testing that, so we make no claim.How long to trial · Trials of muscle recovery ran for more than 7 days and up to 12 weeks. Blood pressure changes in trials are small, so a home monitor over several weeks is the only real way to see whether it does anything for you.

How people take it

Capsule or tablet (quercetin aglycone)About 1,000 mg daily in trialsThe most common supplement form and the one used in the exercise trials. Isolated quercetin is usually the free aglycone.

Combination productFollow the product labelSold with vitamin D3, perilla, bromelain or vitamin C. The one hay fever combination mentioned in a review cannot tell you what quercetin contributed.

Safety

Who should avoid

Kidney disease — animal studies suggest it may worsen damaged kidneys
Hormone-sensitive cancer — animal data suggest it may promote estrogen-dependent tumours
Regular medicines — reported to alter how some drugs are absorbed, ask first
Pregnancy and breastfeeding — no safety data we could find
Long-term high doses — no safety data beyond 12 weeks at 1,000 mg or more

Known interactions

No interactions in our data. Absence of a flag is not clearance.

Questions people ask

Does quercetin lower blood pressure?

A little. A 2022 meta-analysis of 10 trials found systolic pressure fell by about 2.4 mmHg on average. That is a small change and it does not replace prescribed treatment.

Does quercetin help hay fever?

We could not find good evidence that quercetin on its own does. The animal data are encouraging, and a 2025 review of polyphenols in general found modest symptom relief, but with low to very low certainty and no quercetin-only analysis.

Will quercetin boost my immune system?

There is no systematic review we found showing quercetin prevents infections or improves immune markers in athletes. A 2021 review of flavonoids and exercise found little immune data at all, and none favouring quercetin.

Is quercetin safe?

In human studies, side effects are rarely reported and mild. However, a German risk-assessment review found no long-term data on high doses and reported interactions that change how some drugs are absorbed, so check with a pharmacist if you take regular medicines.

Sources

Last reviewed 29 September 2026 · Next review March 2027 · How we rate evidence