Quercetin is a flavonoid, a plant pigment found in onions, apples, berries and tea. As a supplement it is marketed as an antioxidant and for allergies and healthy aging, and in people it has been studied most for blood pressure.
Also known as: quercetin dihydrate, quercetin phytosome.
Quercetin has no intake value or upper limit, and there is no NIH fact sheet for it. A 2018 safety review (Andres) notes that supplements often provide up to 1,000 mg a day, well above usual intake from food, and that there are not enough data on long-term use (over 12 weeks) of 1,000 mg a day or more. These are study protocols, not a recommendation.
It is sold in the US as a dietary supplement. Under the 1994 dietary supplement law (DSHEA), FDA does not approve dietary supplements before they are marketed, and the maker, not FDA, is responsible for safety and labeling. There is no FDA-approved quercetin drug.
A 2016 meta-analysis (Serban) of 7 randomized trials with 587 people found quercetin lowered systolic blood pressure by about 3 mmHg and diastolic by about 2.6 mmHg; the effect was seen mainly at 500 mg a day or more. The authors said more studies are needed to know whether this matters clinically.
The 2018 safety review (Andres) found that side effects in human studies were rare and mild. Animal studies raised possible concerns about worsening existing kidney damage and about estrogen-dependent cancers, and human and animal studies showed quercetin can change how some drugs are absorbed. If you take prescription medicines or have kidney disease, ask your clinician first.
We could not find a single published half-life or time to peak for quercetin that applies to a supplement dose, so we do not list one.
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