Quercetin
A plant flavonoid with antioxidant properties, studied for allergy and respiratory support.
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What it is
Quercetin is a flavonoid pigment found in onions, apples, capers, and tea. It has antioxidant and mast-cell-stabilizing properties, which is why it's studied for allergy and respiratory support.
How it works
Quercetin is a flavonoid plant pigment with antioxidant activity that also appears to stabilize mast cells — immune cells that release histamine — which is the rationale for its use in allergy and respiratory support. It's poorly absorbed on its own, so it's often combined with vitamin C or bromelain, or sold in enhanced-absorption forms.
What it's been studied for
Taken to support respiratory and seasonal-allergy comfort and as an antioxidant.
What the evidence shows
Laboratory data are promising, but human clinical evidence remains limited and less conclusive than for better-studied options. Consider it supportive rather than proven.
Who should consider it
It's used by people looking for seasonal-allergy and respiratory support, and as a general antioxidant; athletes sometimes use it for exercise-related immune stress. Because human evidence is still limited, it's best approached as supportive rather than proven.
Amounts commonly studied
Studies use a wide range, commonly 500-1,000 mg per day; it's often paired with vitamin C or bromelain for absorption.
How to take it
Studies use a wide range, commonly 500-1,000 mg per day, often split and paired with vitamin C or bromelain to aid absorption. Some people take it seasonally during allergy periods. Phytosome forms are marketed for better uptake, since plain quercetin is poorly absorbed.
Forms & absorption
Quercetin dihydrate is common; phytosome forms are marketed for better absorption, since plain quercetin is poorly absorbed.
Food sources
Abundant in onions (especially red), apples with the skin, capers, berries, kale, broccoli, and black and green tea. A produce-rich diet supplies a steady amount.
Safety & interactions
Generally well tolerated at typical doses. High doses may interact with some medications; check with a provider if you take prescriptions.
Myths & what it won't do
Myth: quercetin is a proven natural antihistamine. Reality: the mast-cell rationale is plausible and lab data are promising, but human clinical evidence is limited. Myth: more equals better absorption. Reality: plain quercetin is poorly absorbed regardless of dose, so the form matters more than piling on milligrams.
Common questions
- Does quercetin help allergies?
- It may help by stabilizing histamine-releasing cells, and some people find it useful seasonally, but the human evidence is limited — treat it as supportive rather than a proven antihistamine.
- Why is it combined with bromelain or vitamin C?
- Quercetin is poorly absorbed alone; these are added to try to improve uptake, though the boost is modest.
- When should I take it?
- For allergies, people often start it before and during their trigger season. It can be taken daily with food.
The amounts listed here are what published research has used — not a prescription or a recommended dose for you. Confirm anything you plan to take with your own healthcare provider, especially if you take medications, are pregnant or nursing, or have a health condition.
Related goals
Research on Quercetin
Recommendations on this page are informed by published research. This is educational information, not medical advice.
- Serban MC, Sahebkar A, Zanchetti A, et al. Effects of Quercetin on Blood Pressure: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. J Am Heart Assoc. 2016;5(7):e002713. View study →Note: Found a small drop in blood pressure at doses of 500 mg/day or more; it did not test immune, respiratory, or inflammation claims.