What is Quercetin?

Quercetin is a phytochemical or flavonoid that occurs naturally in foods including apples, onions, tea, berries, and red wine. It is also found in some herbs, such as Ginkgo biloba and St. John’s wort.

Quercetin acts as an antioxidant, neutralizing free radicals – chemical byproducts that damage cell membranes and damage DNA. As a dietary supplement, quercetin also has antihistamine (allergy relief) and anti-inflammatory properties.

This article discusses quercetin uses, research findings, and what to look out for when buying supplements.

What is quercetin used for?

In alternative medicine, quercetin is said to help treat the following conditions:

  • allergy
  • Cardiovascular diseases
  • inflammation
  • cold

So far, results supporting the benefits of quercetin have been mixed. Additionally, its use in certain conditions has only been examined in test-tube (in vitro) or animal studies.

If you are considering using it, please consult your primary care provider first. Self-medicating the disease and avoiding or delaying standard care can have serious consequences.

Here are some research highlights.

allergy relief

Quercetin is thought to prevent the body from releasing histamine, an inflammatory chemical associated with allergy symptoms like sneezing and itching.

Although laboratory experiments have shown that quercetin can fight diseases such as allergic rhinitis, there has been little research on its use in humans. The researchers recommend further studies in people to demonstrate the correlation.


A 2016 review of high-quality trials found that quercetin significantly reduced systolic and diastolic blood pressure. This was especially evident in people with diabetes who took at least 500 milligrams (mg) per day.

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However, the precise dose and duration required to see maximum benefit is unclear.

exercise endurance

According to a 2011 review of studies, quercetin may not be any better than a placebo or sham treatment for improving athletic performance. All 11 studies included showed an increase in exercise tolerance (measured by oxygen consumption) when people took quercetin. However, the effect is minimal.

Another study found an even more impressive link. A 2013 study analyzed 60 male students who had participated in sports for at least three years. After taking quercetin, they saw improvements in lean body mass, hydration levels, calories burned at rest (basal metabolic rate), and total energy expenditure.


Studies of cell cultures suggest that quercetin may help slow the growth of certain types of cancer cells. Several in vitro and animal studies suggest that quercetin may protect against certain types of cancer, such as leukemia and lung cancer.

For example, a 2010 study looked at the relationship between quercetin intake and lung cancer risk. The researchers examined 38 lung tissue samples from patients with adenocarcinoma, a type of cancer. They collected findings from 1,822 lung cancer patients and 1,991 non-lung cancer patients.

Studies have found that a diet rich in quercetin is associated with a lower risk of lung cancer. From the samples, they also identified genetic changes affected by quercetin intake that may protect against lung cancer. The researchers note that more research is needed on this relationship.

Clinical human studies on the anticancer effects of quercetin are currently lacking. Therefore, it is too early to tell whether quercetin might play an important role in cancer prevention.

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Research on quercetin suggests that it may have potential as an add-on treatment for high blood pressure. Further research is needed for allergies, athletic performance and cancer.

possible side effects

Quercetin is generally well tolerated when used in moderation. Some people report tingling in the arms and legs, as well as stomach upset and headaches when taking quercetin supplements.

Very high doses (more than 1 gram per day) may cause kidney damage.

Avoid taking quercetin if you are pregnant, nursing, or have kidney disease. It may also interfere with some antibiotics or blood thinners.

Talk to your doctor before using quercetin supplements. Be sure to mention any medications you are taking and any conditions you have.

Dosage and Preparation

Under medical supervision, quercetin is safe to use in up to 1,000 mg twice daily for 12 weeks. There isn’t enough evidence to know if it’s safe for long-term use.

The dose that is right for you may depend on factors such as your age, sex, and medical history. If you choose to take this supplement, please consult your healthcare provider for individualized advice.

what to look for

Food sources of quercetin include tea, onions, apples, buckwheat, and pau d’arco.

When taking quercetin in supplement form, it may be beneficial to choose a product that contains both papain and/or bromelain. These are plant-derived enzymes (fruit extracts) that increase intestinal absorption of quercetin.

Keep in mind that dietary supplements are largely unregulated. The content of some products may differ from the content on the product label and its safety cannot be guaranteed. Choosing products certified by independent third parties such as NSF can ensure that the content of the product is as pure as advertised.


Quercetin is a phytochemical that occurs naturally in certain foods and beverages, such as apples and tea. It is thought to help improve certain health conditions, including allergies, cardiovascular disease, and inflammation.

Research on the actual health benefits of quercetin is conflicting. Researchers have found that quercetin helps lower blood pressure, especially in people with diabetes. However, it is not clear what dose is required to obtain maximum benefit.

Consult your doctor before using any supplements, including quercetin.

Frequently Asked Questions

  • Does Quercetin Have Any Side Effects?

    Side effects of quercetin may include headache and upset stomach. It’s generally considered safe for most people, but those who are pregnant or breastfeeding and those with kidney disease should avoid it. Quercetin can interact with antibiotics or blood thinners, so if you take these, talk to your doctor before trying quercetin.

  • Which foods contain quercetin?

    Foods that contain quercetin include apples, onions, red wine, tea, and berries. It can also be found in the herbs Ginkgo biloba and St. John’s wort.

  • What is a safe dose of quercetin?

    Quercetin intake should not exceed 1 gram per day, as exceeding this amount can cause kidney damage. When taking dietary supplements, always follow the directions on the product packaging.