Overview

Quercetin is a chemical that is naturally found in many plants and is also available over-the-counter as a supplement. People take quercetin for many different reasons, although its benefits are not well defined. It seems to be well tolerated, but there is not enough research to know what side effects it may cause. Before taking quercetin, make sure to tell your health care provider about any health conditions you have or medicines you are taking.

Uses

What is quercetin used for?

Quercetin, a chemical that is naturally found in various plants, is used for many different reasons. However, the benefits of quercetin are not well defined. Some common reasons that people use quercetin include the following.

• Heart disease
• Prostate problems
• To strengthen the immune system
• To improve memory and thinking skills
• To reduce muscle damage from exercise

Note: The FDA has not reviewed quercetin for safety and effectiveness. Learn more about dietary supplements here.

Quercetin is available as a dietary supplement in various strengths and dosage forms. It is also often  combined with other ingredients in some multivitamins or supplements.

How does quercetin work (mechanism of action)?

Quercetin is a type of chemical called a flavonoid. It is naturally found in many different foods, including  onions, kale, tomatoes, broccoli, blueberries, and corn. It is also found in some herbal products that are sold as dietary supplements, such as ginkgo.

Quercetin can reduce swelling (inflammation) and act as an antioxidant. It may also change the way that your brain responds to certain chemicals, such as serotonin. This has led to interest in using quercetin for many different reasons, including improving the health of the heart, brain, prostate, and immune system. But the benefits of quercetin for any use are not well defined.

How should I store quercetin?

You should store quercetin according to the product label. Most dietary supplements should be kept in a cool, dry location that is out of the reach of children and pets and not in direct sunlight.

Side Effects

What are the most common side effects of quercetin?

Quercetin seems to be well tolerated. But there is not enough research to know what the common side effects may be. Tell your health care provider if you have any side effects that bother you.

There may be side effects of quercetin that are not listed here. Contact your health care provider if you think you are having a side effect of a supplement. In the U.S., you can report side effects to the FDA at www.safetyreporting.hhs.gov or by calling 888-SAFEFOOD (888-723-3366). In Canada, you can report side effects to Health Canada at www.health.gc.ca/medeffect or by calling 866-234-2345.

What are the serious side effects of quercetin?

While less common, the most serious side effects of quercetin are described below, along with what to do if they happen.

Severe Allergic Reactions. Quercetin may cause allergic reactions, which can be serious. Stop taking quercetin and get help right away if you have any of the following symptoms of a serious allergic reaction.

• Breathing problems or wheezing
• Racing heart
• Fever or general ill feeling
• Swollen lymph nodes
• Swelling of the face, lips, mouth, tongue, or throat
• Trouble swallowing or throat tightness
• Itching or skin rash
• Bumps on the skin called hives that can be red, pink, white, or brown depending on your skin tone
• Nausea or vomiting
• Dizziness, feeling lightheaded, or fainting
• Stomach cramps
• Joint pain

Precautions

Who should not use quercetin?

Allergies to Ingredients. People who are allergic to any of the following should not take quercetin.

• Meletin
• Quercetin
• Sophoretin
• Any of the ingredients in the specific product

Your pharmacist can tell you all of the ingredients in the specific quercetin products they stock.

What should I know about quercetin before using it?

Quercetin is a dietary supplement. It cannot be marketed to treat or cure a disease.

Read and follow the directions on the specific product you are taking, or take it as recommended by your health care provider.

Keep quercetin out of the reach of children.

The FDA has not tested quercetin products to confirm that they contain the ingredients stated on their labels. Some dietary supplements have been tested by third-party organizations to confirm that they contain the ingredients listed on their labels and do not contain any harmful chemicals. Learn more about how to choose a safe dietary supplement product here.

What should I tell my health care provider before using quercetin?

Tell your health care provider about all of your health conditions and any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. This will help them know if quercetin is right for you.

In particular, make sure that you discuss any of the following.

Current and Past Health Conditions.Tell your health care provider if you have any of the following.

• Hormone-sensitive cancers, including breast,ovarian, or uterine cancer
• Are receiving treatment for cancer, including radiation or chemotherapy

Other Medicines and Supplements.Quercetin may interact with other medicines and supplements. Before taking quercetin, tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. See the Interactions section for more details.

Pregnancy. It is not known if or how quercetin could affect pregnancy or harm an unborn baby. Tell your health care provider if you are pregnant or plan to become pregnant.

Breastfeeding. Quercetin passes into breast milk. Tell your health care provider if you are breastfeeding or plan to breastfeed.

Interactions

Does quercetin interact with foods or drinks?

There are no known interactions between quercetin and foods or drinks.

It is unknown if drinking alcohol will affect quercetin.

Does quercetin interact with medicines (drug interactions)?

Always tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using.

In particular, make sure that you discuss if you are receiving chemotherapy, which is a type of medicine used to treat cancer.

The interactions between quercetin and medicines are not fully understood. As with most dietary supplements, the research on drug interactions with quercetin is incomplete. Always check with your health care provider before taking quercetin with any medicines.

Dosing

What should I do if I accidentally use too much quercetin?

If you or someone else has used too much quercetin, get medical help right away, call 911, or contact a Poison Control center at 800-222-1222.

Quercetin is found naturally in some foods, including onions, kale, broccoli, corn, and blueberries. It is also available as a dietary supplement. The dose of quercetin can be very different depending on the product you choose and your reasons for using it. Read the product label closely and speak with a health care provider about how to take quercetin safely. Do not take double or extra doses, even if you miss a dose.