URL of this page: https://medlineplus.gov/druginfo/natural/294.html

Quercetin

What is it?

Quercetin is a plant pigment (flavonoid). It is found in many plants and foods, such as red wine, onions, green tea, apples, berries, Ginkgo biloba, St. John's wort, American elder, and others. Buckwheat tea has a large amount of quercetin. Some people use quercetin as a medicine.

Quercetin is most commonly used for conditions of the heart and blood vessels and to prevent cancer. It is also used for arthritis, bladder infections, and diabetes, but there is limited scientific evidence to support these uses.

Coronavirus disease 2019 (COVID-19): Quercetin may have benefit for some airway infections, but there is no good evidence to support using it for COVID-19. Follow healthy lifestyle choices and proven prevention methods instead.

How effective is it?

Natural Medicines Comprehensive Database rates effectiveness based on scientific evidence according to the following scale: Effective, Likely Effective, Possibly Effective, Possibly Ineffective, Likely Ineffective, Ineffective, and Insufficient Evidence to Rate.

The effectiveness ratings for QUERCETIN are as follows:

Possibly ineffective for...

  • Athletic performance. Most clinical research shows that taking quercetin before exercise does not decrease fatigue or improve exercise ability.

Insufficient evidence to rate effectiveness for...

  • Asthma. Early research shows that taking quercetin might improve asthma symptoms and reduce the use of rescue inhalers in people with asthma.
  • A blood disorder that reduces levels of protein in the blood called hemoglobin (beta-thalassemia). Some people with beta-thalassemia need blood transfusions. These transfusions can cause too much iron to build up in the body. Early research shows that taking quercetin might reduce iron levels in people with beta-thalassemia who need blood transfusions.
  • Heart disease. Some research suggests that eating foods rich in quercetin, such as tea, onions and apples, may reduce the risk of death due to heart disease in elderly men. However, taking a daily quercetin supplement does not seem to improve heart disease risk factors in people who are healthy.
  • Kidney damage caused by contrast dyes (contrast induced nephropathy). Early research shows that taking quercetin before and after receiving contrast dye doesn't prevent kidney damage caused by the dye.
  • Muscle damage caused by exercise. Taking quercetin doesn't seem to help to prevent muscle soreness due to cycling or running. But it might prevent muscle damage and improve muscle strength recovery with certain types of weight training.
  • Airway infections caused by exercise. Early research shows that taking quercetin may reduce the chance for upper respiratory infections after heavy exercise.
  • High cholesterol. Short-term use of quercetin does not appear to lower "bad cholesterol" (low-density lipoprotein (LDL) cholesterol) or total cholesterol, or to raise "good cholesterol" (high-density lipoprotein (HDL) cholesterol). But most of the studies conducted have been small and included people without high cholesterol. It's unclear if quercetin would show benefit in only people with high cholesterol.
  • High blood pressure. Early research suggests that taking quercetin produces a small decrease in blood pressure in people with untreated, mild high blood pressure. It's unclear if this reduction in blood pressure is clinically meaningful.
  • Lung cancer. Higher intake of quercetin as part of the diet has been linked with a lower risk of lung cancer in people who smoke.
  • A grouping of symptoms that increase the risk of diabetes, heart disease, and stroke (metabolic syndrome). Taking quercetin doesn't appear to improve blood sugar or insulin levels in people who are at risk for metabolic syndrome. This includes people with diabetes, obesity, polycystic ovary syndrome (PCOS), or high blood pressure. But quercetin might help lower blood sugar in people with risk factors for metabolic syndrome who are under 45 years of age, those who take quercetin for 8 or more weeks, or those taking at least 500 mg of quercetin per day. It's unclear if quercetin helps with blood sugar in people who have already been diagnosed with metabolic syndrome.
  • Swelling (inflammation) and sores inside the mouth (oral mucositis). Early research suggests that taking quercetin does not prevent mouth sores caused by cancer drugs.
  • Ovarian cancer. One population study found no link between quercetin intake from the diet and the chance of ovarian cancer.
  • Pancreatic cancer. Some research suggests that eating high amounts of quercetin in the diet might reduce the chance of developing pancreatic cancer, especially in men who smoke.
  • A hormonal disorder that causes enlarged ovaries with cysts (polycystic ovary syndrome or PCOS). Research shows that taking quercetin improves hormone levels in women with PCOS by a small amount. In some people it might also improve how sensitive the body is to insulin. But it's unclear if these changes lead to improvements in symptoms of PCOS such as irregular periods.
  • Swelling (inflammation) of the prostate due to infection. Taking quercetin by mouth seems to reduce pain and improve quality of life, but doesn't seem to help urination problems in men with ongoing prostate problems that aren't due to infection.
  • Rheumatoid arthritis (RA). Research shows that taking quercetin reduces pain and stiffness in women with RA. But it doesn't seem to reduce the number of swollen or tender joints.
  • Alzheimer disease.
  • Autism.
  • Cancer.
  • Canker sores.
  • Cataracts.
  • Chronic fatigue syndrome (CFS).
  • Cold sores (herpes labialis).
  • Colon cancer, rectal cancer.
  • Diabetes.
  • Enlarged prostate (benign prostatic hyperplasia or BPH).
  • Flushing caused by the drug niacin.
  • Gout.
  • Hardening of the arteries (atherosclerosis).
  • Hay fever.
  • Infections of the kidney, bladder, or urethra (urinary tract infections or UTIs).
  • Kidney transplant.
  • Obesity.
  • Painful urination due to swelling (inflammation) of the urethra (urethral syndrome).
  • Poor circulation that can cause the legs to swell (chronic venous insufficiency or CVI).
  • Schizophrenia.
  • Stomach ulcers.
  • Upper airway infection.
  • Other conditions.
More evidence is needed to rate quercetin for these uses.

How does it work?

Quercetin has antioxidant and anti-inflammatory effects which might help reduce inflammation, kill cancer cells, control blood sugar, and help prevent heart disease.

Are there safety concerns?

When taken by mouth: Quercetin is POSSIBLY SAFE for most people when taken short-term. Quercetin has been safely used in amounts up to 500 mg twice daily for 12 weeks. It is not known if long-term use or higher doses are safe.

When given by IV: Quercetin is POSSIBLY SAFE when given in appropriate amounts. Side effects may include flushing, sweating, nausea, vomiting, difficulty breathing, or pain at the injection site. But large doses are POSSIBLY UNSAFE. There have been reports of kidney damage at higher doses.

When applied to the skin: There isn't enough reliable information to know if quercetin is safe or what the side effects might be.

Special precautions & warnings:

Pregnancy and breast-feeding: There isn't enough reliable information to know if quercetin is safe to use when pregnant or breast-feeding. Stay on the safe side and avoid use.

Kidney problems: Quercetin might make kidney problems worse. Don't use quercetin if you have kidney problems.

Are there interactions with medications?

Moderate
Be cautious with this combination.
Antibiotics (Quinolone antibiotics)
Taking quercetin along with some antibiotics might decrease the effectiveness of some antibiotics. Some scientists think that quercetin might prevent some antibiotics from killing bacteria. But it's too soon to know if this is a big concern.

Some of these antibiotics that might interact with quercetin include ciprofloxacin (Cipro), gemifloxacin (Factive), levofloxacin (Levaquin), moxifloxacin (Avelox), and others.
Cyclosporine (Neoral, Sandimmune)
Quercetin might decrease how quickly the body breaks down cyclosporine. Taking quercetin with cyclosporine might increase the effects and side effects of cyclosporine.
Diclofenac (Voltaren, others)
Quercetin might decrease how quickly the body breaks down diclofenac. Taking quercetin with diclofenac might increase the effects and side effects of diclofenac.
Losartan (Cozaar)
Quercetin might increase how much losartan is absorbed into the body and decrease how quickly the body breaks down losartan. Losartan is normally broken down into another chemical (active metabolite) that has stronger effects on blood pressure than losartan. By decreasing how quickly the body breaks down losartan, quercetin also seems to decrease levels of losartan's active metabolite. Taking quercetin with losartan might increase the effects and side effects of losartan while decreasing the effects of losartan's active metabolite.
Medications changed by the liver (Cytochrome P450 2C8 (CYP2C8) substrates)
Some medications are changed and broken down by the liver. Quercetin might decrease how quickly the liver breaks down some medications. Taking quercetin along with some medications that are broken down by the liver can increase the effects and side effects of these medications. Before taking quercetin, talk with your healthcare provider if you take any medications that are changed by the liver.

Some medications that are changed by the liver include paclitaxel (Taxol), rosiglitazone (Avandia), amiodarone (Cordarone), docetaxel (Taxotere), tretinoins, repaglinide (Prandin), verapamil (Calan, Isoptin, Verelan, etc.), and others.
Medications changed by the liver (Cytochrome P450 2C9 (CYP2C9) substrates)
Some medications are changed and broken down by the liver. Quercetin might decrease how quickly the liver breaks down some medications. Taking quercetin along with some medications that are broken down by the liver can increase the effects and side effects of these medications. Before taking quercetin, talk with your healthcare provider if you take any medications that are changed by the liver.

Some medications that are changed by the liver include celecoxib (Celebrex), diclofenac (Voltaren), fluvastatin (Lescol), glipizide (Glucotrol), ibuprofen (Advil, Motrin), irbesartan (Avapro), losartan (Cozaar), phenytoin (Dilantin), piroxicam (Feldene), tamoxifen (Nolvadex), tolbutamide (Tolinase), torsemide (Demadex), and warfarin (Coumadin).
Medications changed by the liver (Cytochrome P450 2D6 (CYP2D6) substrates)
Some medications are changed and broken down by the liver. Quercetin might decrease how quickly the liver breaks down some medications. Taking quercetin along with some medications that are broken down by the liver can increase the effects and side effects of these medications. Before taking quercetin, talk with your healthcare provider if you take any medications that are changed by the liver.

Some drugs that are changed by the liver include amitriptyline (Elavil), codeine, flecainide (Tambocor), haloperidol (Haldol), imipramine (Tofranil), metoprolol (Lopressor, Toprol XL), ondansetron (Zofran), paroxetine (Paxil), risperidone (Risperdal), tramadol (Ultram), venlafaxine (Effexor), and others.
Medications changed by the liver (Cytochrome P450 3A4 (CYP3A4) substrates)
Some medications are changed and broken down by the liver. Quercetin might change how quickly the liver breaks down some medications. Taking quercetin along with some medications that are broken down by the liver can increase or decrease the effects and side effects of these medications. Before taking quercetin, talk with your healthcare provider if you take any medications that are changed by the liver.

Some drugs that are changed by the liver include calcium channel blockers (diltiazem, nicardipine, verapamil), chemotherapeutic agents (etoposide, paclitaxel, vinblastine, vincristine, vindesine), antifungals (ketoconazole, itraconazole), glucocorticoids, alfentanil (Alfenta), fentanyl (Sublimaze), losartan (Cozaar), fluoxetine (Prozac), midazolam (Versed), omeprazole (Prilosec), lansoprazole (Prevacid), ondansetron (Zofran), propranolol (Inderal), fexofenadine (Allegra), amitriptyline (Elavil), amiodarone (Cordarone), citalopram (Celexa), sertraline (Zoloft), quetiapine (Seroquel), and numerous others.
Medications for diabetes (Antidiabetes drugs)
Quercetin might lower blood sugar in people with diabetes. Diabetes medications are also used to lower blood sugar. Taking quercetin along with diabetes medications might cause blood sugar to go too low. Monitor your blood sugar closely. The dose of your diabetes medication might need to be changed.
Some medications used for diabetes include glimepiride (Amaryl), glyburide (DiaBeta, Glynase PresTab, Micronase), insulin, pioglitazone (Actos), rosiglitazone (Avandia), chlorpropamide (Diabinese), glipizide (Glucotrol), tolbutamide (Orinase), and others.
Medications for high blood pressure (Antihypertensive drugs)
Quercetin seems to decrease blood pressure. Taking quercetin along with medications for high blood pressure might cause your blood pressure to go too low.

Some medications for high blood pressure include captopril (Capoten), enalapril (Vasotec), losartan (Cozaar), valsartan (Diovan), diltiazem (Cardizem), Amlodipine (Norvasc), hydrochlorothiazide (HydroDIURIL), furosemide (Lasix), and many others.
Medications moved by pumps in cells (Organic Anion Transporter 1 (OAT1) Substrates)
Some medications are moved by pumps in cells. Quercetin might change how these pumps work and affect how much of some medications get cleared from the body. This could make these medications stay in the blood longer, which could increase the effects and side effects of these medications.

Some of these medications include ciprofloxacin, ibuprofen, methotrexate, and pravastatin (Pravachol).
Medications moved by pumps in cells (Organic Anion Transporter 3 (OAT3) Substrates)
Some medications are moved by pumps in cells. Quercetin might change how these pumps work and affect how much of some medications get cleared from the body. This could make these medications stay in the blood longer, which could increase the effects and side effects of these medications.

Some of these medications include adefovir (Lamivudine), zidovudine (Retrovir), ciprofloxacin, methotrexate, and pravastatin (Pravachol).
Medications moved by pumps in cells (Organic anion-transporting polypeptide substrates)
Some medications are moved by pumps in cells. Quercetin might change how these pumps work and affect how much of some medications get cleared from the body. This could make these medications stay in the blood for longer, which could increase the effects and side effects of these medications.

Some of these medications that are moved by pumps in cells include bosentan (Tracleer), celiprolol (Celicard, others), etoposide (VePesid), fexofenadine (Allegra), fluoroquinolone antibiotics, glyburide (Micronase, Diabeta), irinotecan (Camptosar), methotrexate, paclitaxel (Taxol), saquinavir (Fortovase, Invirase), rifampin, statins, talinolol, torsemide (Demadex), troglitazone, and valsartan (Diovan).
Medications moved by pumps in cells (P-glycoprotein substrates)
Quercetin might affect the way certain medications are processed by the body. Quercetin might make these medications easier for the body to use and make them last longer in the body.

Some of the drugs that may be affected in these ways by quercetin include paclitaxel, diltiazem, cyclosporine, saquinavir, digoxin, cancer drugs (etoposide, vinblastine, vincristine, vindesine), antifungals (ketoconazole, itraconazole), protease inhibitors (amprenavir, indinavir, nelfinavir), H2 antagonists (cimetidine, ranitidine), verapamil, corticosteroids, erythromycin, fexofenadine (Allegra), loperamide (Imodium), quinidine, quetiapine (Seroquel), and others.
Midazolam (Versed)
Quercetin might increase how quickly the body breaks down midazolam. Taking quercetin with midazolam might reduce the effects of midazolam.
Pravastatin (Pravachol)
Some drugs are taken up by the liver to be broken down and cleared from the body. Quercetin might decrease how quickly pravastatin is taken up by the liver. This might increase how long pravastatin stays in the blood which could increase the effects and side effects of pravastatin.
Quetiapine (Seroquel)
Quercetin might increase levels of quetiapine. Taking quercetin and quetiapine together might increase the effects and side effects of quetiapine.
Warfarin (Coumadin)
Quercetin might increase the effects that warfarin has on the body. Taking quercetin and warfarin together might increase the chance of side effects of warfarin such as bruising and bleeding.

Are there interactions with herbs and supplements?

Herbs and supplements that might lower blood pressure
Quercetin can slightly lower blood pressure in people with high blood pressure. Taking quercetin along with other herbs and supplements that lower blood pressure might cause your blood pressure to go too low.

Other herbs and supplements that can lower blood pressure include andrographis, casein peptides, cat's claw, coenzyme Q-10, fish oil, L-arginine, lyceum, stinging nettle, theanine, and others.
Herbs and supplements that might lower blood sugar
Quercetin might lower blood sugar in people with diabetes. Taking quercetin along with other herbs and supplements that can lower blood sugar might cause your blood sugar to go too low.
Other herbs and supplements that might lower blood sugar include agaricus mushroom, devil's claw, fenugreek, guar gum, Panax ginseng, Siberian ginseng, and others.

Are there interactions with foods?

There are no known interactions with foods.

What dose is used?

The appropriate dose of quercetin depends on several factors such as the user's age, health, and several other conditions. At this time there is not enough scientific information to determine an appropriate range of doses for quercetin. Keep in mind that natural products are not always necessarily safe and dosages can be important. Be sure to follow relevant directions on product labels and consult your pharmacist or physician or other healthcare professional before using.

Other names

3,3',4'5,7-Pentahydroxyflavone, Bioflavonoid, Bioflavonoid Complex, Bioflavonoid Concentrate, Bioflavonoid Extract, Bioflavonoïde, Bioflavonoïde de Citron, Bioflavonoïdes de Citron, Citrus Bioflavones, Citrus Bioflavonoid, Citrus Bioflavonoids, Citrus Bioflavonoid Extract, Citrus Flavones, Citrus Flavonoids, Complexe de Bioflavonoïde, Concentré de Bioflavonoïde, Extrait de Bioflavonoïde, Extrait de Bioflavonoïdes de Citron, Flavones de Citron, Flavonoid, Flavonoïde, Meletin, Mélétine, Quercetina, Quercétine, Sophretin, Sophrétine.

Methodology

To learn more about how this article was written, please see the Natural Medicines Comprehensive Database methodology.

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Last reviewed - 04/14/2021