Medically Reviewed by Jabeen Begum, MD on June 11, 2024
5 min read

Quercetin is a plant pigment (flavonoid) that people sometimes take as a medicine. Flavonoids are antioxidants that neutralize and help avoid damage from free radicals. Free radicals are particles in your body that harm and even kill cells and cell membranes.

It is the most common flavonoid found in many plants and foods. Most studies look at the impact of flavonoids such as quercetin within the diet rather than as a supplement.

Much of the research on quercetin's health benefits has been done in animals or cell cultures. We need more studies to prove quercetin's benefits and safety in humans, especially when taken as a supplement instead of in food.

People take quercetin to try to manage a variety of issues, including:

  • Heart and vessel problems
  • High blood pressure
  • Prostate infections
  • Upper respiratory infections
  • Allergies
  • Disease prevention

Prostate health

Early evidence suggests that quercetin might help ease symptoms of prostatitis, which is prostate inflammation. A small study showed that men who took quercetin had fewer symptoms than those who took a placebo. But researchers will need to carry out more studies.

May improve athletic performance

Some athletes try to increase endurance and improve athletic performance by using quercetin. Although animal studies are promising, the effects in humans, if any, are likely small. One of the biggest benefits of quercetin for atheltes may be that it may help prevent certain infections such as an upper respiratory infection or cold after intense workouts.

Could be anti-cancerous

Some studies link a diet high in quercetin with a lowered risk of cancer. But more research is needed. Cancer research in animal models has been promising but has not yet panned out for human trials. The latest meta-analysis looks at ovarian cancer and shows no detectable benefit.

May protect heart health

Early quercetin research on heart and vessel disease is mixed. Some study results are positive, but some are open to debate. For example, researchers link eating lots of foods high in quercetin to a lower risk of heart-related death in older men. But other studies are less convincing.

May reduce inflammation

Quercetin can help stabilize cells that release histamine in the body, which gives it anti-inflammatory and antihistamine effects.

May protect brain health

Researchers have found that quercetin may protect brain cells from damage and death, which could help slow the progression of Parkinson's disease and improve motor function.

Quercetin for allergies

In lab tests, quercetin stops immune cells from releasing histamines, the chemicals that trigger allergic reactions. Because of this, researchers believe quercetin might help ease allergy symptoms such as runny nose, watery eyes, hives, and swelling of the face and lips.

Common oral dosages are up to 500 milligrams twice a day, but people have also used lower dosages. However, optimal doses of quercetin have not been established for any condition. Quality and active ingredients in supplements may vary widely from maker to maker, making it hard to establish a standard dose.

Don't take more than the suggested dose of quercetin, and talk to your doctor before taking any supplement.

Quercetin is abundant in nature and foods. People typically get between 5 and 40 milligrams a day from food. But if you eat lots of fruits and vegetables, you can get as much as 500 milligrams daily.

For example, think "quercetin" the next time you pour a glass of red wine, bite into a crunchy apple, treat yourself to some berries, flip a buckwheat pancake, slice an onion, or sip a cup of green tea. Other fruits and vegetables that have high amounts of quercetin include:

Fruit sources of quercetin

  • Tomatoes
  • Red grapes
  • Cherries
  • Capers

Vegetable sources of quercetin

  • Kale
  • Broccoli
  • Raw Asparagus
  • Raw red onion

Other natural sources of quercetin

  • Nuts and seeds
  • Olive oil
  • American elder
  • St. John's wort
  • Ginkgo biloba

Quercetin supplements come in pill or capsule form and are often combined with bromelain, an anti-inflammatory enzyme from pineapple. Water-soluble forms of quercetin, such as hesperidin-methyl-chalcone (HMC) or quercetin-chalcone, are also available.

When you take it through food, quercetin is likely safe. As a supplement, quercetin may be safe if you take reasonable amounts for a short time, such as 500 milligrams twice a day for 12 weeks. Taken longer, the risks are unknown.

Side effects. Quercetin may cause headache s or tingling in your arms and legs. Other side effects may occur if you receive quercetin treatment by IV (intravenously).

Risks. Kidney damage may result from high doses. 

The FDA regulates supplements in a way that is different from "conventional" foods and drugs. Be sure to tell your doctor about any supplements you're taking, even if they're natural. That way, your doctor can check for potential side effects or interactions with medications, foods, or other herbs and supplements. They can let you know if the supplement might raise your risks.

If you are pregnant or breastfeeding, don't take quercetin as a supplement. You may get too much, as quercetin is in so many foods.

Be careful if you are taking drugs such as antibiotics, cyclosporine, warfarin, or drugs that are changed by the liver. Quercetin may change how these drugs work and raise the risk of side effects.

There don't appear to be interactions between quercetin and foods or other herbs and supplements.

Quercetin is a plant pigment found in many foods. Some people also take it as a supplement. People take it for various health issues, such as heart problems, high blood pressure, prostate infections, respiratory infections, allergies, and disease prevention. Research on how well quercetin works is mixed, with some promising results in animals and limited benefits in humans. Quercetin is generally safe when consumed in foods, but high doses as a supplement can cause health problems, including potential kidney damage and interactions with certain medications.