Quercetin

Print

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. People use quercetin as a medicine.

Quercetin is most commonly taken by mouth to treat conditions of the heart and blood vessels and 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.

It is effective?
Natural Medicines 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.

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 Make a Determination 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.
  • Kidney transplant. Some research suggests that taking a product containing quercetin and curcumin, starting within 24 hours of kidney transplantation, improves early function of the transplanted kidney when taken in combination with anti-rejection drugs.
  • 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.
  • Autism.
  • Cataracts.
  • Chronic fatigue syndrome (CFS).
  • Diabetes.
  • Enlarged prostate (benign prostatic hyperplasia or BPH).
  • Gout.
  • Hardening of the arteries (atherosclerosis).
  • Hay fever.
  • Infections of the kidney, bladder, or urethra (urinary tract infections or UTIs).
  • Painful urination due to swelling (inflammation) of the urethra (urethral syndrome).
  • Schizophrenia.
  • Stomach and intestinal ulcers.
  • Viral infections.
  • 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.

Is there concern for the safety of its use?
When taken by mouth: Quercetin is POSSIBLY SAFE for most people when taken by mouth 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 taken by mouth, quercetin can cause headache and tingling of the arms and legs. Very high doses might cause kidney damage.

When given by IV: Quercetin is POSSIBLY SAFE when given intravenously (by IV) in appropriate amounts (less than 722 mg). Side effects may include flushing, sweating, nausea, vomiting, difficulty breathing, or pain at the injection site. But larger amounts given by IV are POSSIBLY UNSAFE. There have been reports of kidney damage at higher doses.

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 any drug interactions?

Antibiotics (Quinolone antibiotics)

Interaction Rating=Moderate Be cautious with this combination.

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), enoxacin (Penetrex), norfloxacin (Chibroxin, Noroxin), sparfloxacin (Zagam), trovafloxacin (Trovan), and grepafloxacin (Raxar).

Cyclosporin (Neoral, Sandimmune)

Interaction Rating=Moderate Be cautious with this combination.

Cyclosporin (Neoral, Sandimmune) is changed and broken down by the liver. Quercetin might decrease how quickly the liver breaks down cyclosporin (Neoral, Sandimmune). Taking quercetin might increase the effects and side effects of this medication. Before taking quercetin talk to your healthcare provider if you take cyclosporin (Neoral, Sandimmune).

Medications changed by the liver (Cytochrome P450 2C8 (CYP2C8) substrates)

Interaction Rating=Moderate Be cautious with this combination.

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 these medications that are changed by the liver might increase the effects and side effects of your medication. Before taking quercetin talk to 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), repaglinide (Prandin), verapamil (Calan, Isoptin, Verelan), and others.

Medications changed by the liver (Cytochrome P450 2C9 (CYP2C9) substrates)

Interaction Rating=Moderate Be cautious with this combination.

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 these medications that are changed by the liver might increase the effects and side effects of your medication. Before taking quercetin talk to 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), warfarin (Coumadin), and others.

Medications changed by the liver (Cytochrome P450 2D6 (CYP2D6) substrates)

Interaction Rating=Moderate Be cautious with this combination.

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 these medications that are changed by the liver might increase the effects and side effects of your medication. Before taking quercetin talk to your healthcare provider if you take any medications that are changed by the liver.
Some medications 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)

Interaction Rating=Moderate Be cautious with this combination.

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 these medications that are changed by the liver might increase the effects and side effects of your medication. Before taking quercetin talk to your healthcare provider if you take any medications that are changed by the liver.
Some medications that are changed by the liver include lovastatin (Mevacor), clarithromycin (Biaxin), cyclosporine (Neoral, Sandimmune), diltiazem (Cardizem), estrogens, indinavir (Crixivan), triazolam (Halcion), verapamil (Calan, Isoptin, Verelan), 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), ketoconazole (Nizoral), itraconazole (Sporanox), and numerous others.

Medications moved by pumps in cells (P-glycoprotein Substrates))

Interaction Rating=Moderate Be cautious with this combination.

Some medications are moved by pumps in cells. Quercetin might make these pumps less active and increase how much of some medications get absorbed by the body. This might cause more side effects from some medications.
Some medications that are moved by these pumps include diltiazem (Cardizem), verapamil (Calan, Isoptin, Verelan), digoxin (Lanoxin) cyclosporine (Neoral, Sandimmune), saquinavir (Invirase), amprenavir (Agenerase), nelfinavir (Viracept), loperamide (Imodium), quinidine, paclitaxel (Taxol), vincristine, etoposide (VP16, VePesid), cimetidine (Tagamet), ranitidine (Zantac), fexofenadine (Allegra), ketoconazole (Nizoral), itraconazole (Sporanox), and others.

Are there any 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 any interactions with food?
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.

By what other names is the product known?
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.

Natural Medicines disclaims any responsibility related to medical consequences of using any medical product. Effort is made to ensure that the information contained in this monograph is accurate at the time it was published. Consumers and medical professionals who consult this monograph are cautioned that any medical or product related decision is the sole responsibility of the consumer and/or the health care professional. A legal License Agreement sets limitations on downloading, storing, or printing content from this Database. Except for any possible exceptions written into your License Agreement, no reproduction of this monograph or any content from this Database is permitted without written permission from the publisher. Unlawful to download, store, or distribute content from this site.

For the latest comprehensive data on this and every other natural medicine, health professionals should consult the Professional Version of the Natural Medicines. It is fully referenced and updated daily.

© Copyright 1995-2021. Therapeutic Research Faculty, publishers of Natural Medicines, Prescriber’s Letter, and Pharmacist’s Letter. All rights reserved.