The Who, What, Where, When and Sometimes, Why.

Quercetin

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. 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.

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.

The Effectiveness ratings for Quercetin are as follows:

Possibly Ineffective for…

  • Exercise performance. Most clinical research shows that taking quercetin before exercise does not improve fatigue, reduce muscle soreness, or decrease swelling.

Insufficient Evidence to Rate Effectiveness for…

  • Autism. Early research shows that taking a product containing quercetin and other ingredients might improve behavior and social interactions in children with autism.
  • Enlarged prostate (benign prostatic hyperplasia or BPH). Early research shows that taking a product containing quercetin, beta-sitosterol, and saw palmetto doesn’t help with urination and other symptoms in men with BPH.
  • 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.
  • Diabetes. Early research shows that taking a combination of quercetin, myricetin, and chlorogenic acid helps to lower blood sugar in people with diabetes who are not taking antidiabetes drugs. Taking the same combination also seems to benefit people with diabetes who are already taking metformin.
  • Exercise-induced respiratory infections. 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 transplantation. 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.
  • Inflamed mouth sores (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.
  • An ovary disorder known as polycystic ovary syndrome (PCOS). Research shows that taking quercetin improves hormone levels in women with PCOS. It also seems to 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.
  • Prostate pain and swelling (inflammation). 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.
  • Painful urination due to problems with the urethra (urethral syndrome). Early research shows that taking a product containing quercetin, bromelain, chondroitin sulfate, gotu kola, rhodiola, and barbed skullcap helps reduce how often people with urethral syndrome need to urinate.
  • Urinary tract infections (UTIs). Early research suggests that taking a combination of hyaluronic acid, chondroitin sulfate, curcumin, and quercetin by mouth, and applying estrogen to the vagina, helps to prevent UTIs in women who get them often. The quercetin product also works without the estrogen, but not as well.
  • Asthma.
  • Cataracts.
  • Chronic fatigue syndrome (CFS).
  • Gout.
  • “Hardening of the arteries ” (atherosclerosis).
  • Hay fever (allergic rhinitis).
  • Pain and swelling (inflammation).
  • Schizophrenia.
  • Stomach and intestinal ulcers.
  • Viral infections.
  • Other conditions.

More evidence is needed to rate quercetin for these uses.

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

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 longer-term use or larger amounts are safe.

Quercetin can cause headache and tingling of the arms and legs. Very high doses might cause kidney damage.

When given intravenously (by IV) in appropriate amounts (less than 722 mg), quercetin is POSSIBLY SAFE. 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: Not enough is known about the use of quercetin during pregnancy and 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.

Antibiotics (Quinolone antibiotics)

Interaction Rating = Moderate Be cautious with this combination.

Talk to your health provider.

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)

Interaction Rating = Moderate Be cautious with this combination.

Talk to your health provider.

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)

Interaction Rating = Moderate Be cautious with this combination.

Talk to your health provider.

Quercetin might decrease how quickly the body breaks down diclofenac. Taking quercetin with diclofenac might increase the effects and side effects of diclofenac.

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

Interaction Rating = Moderate Be cautious with this combination.

Talk to your health provider.

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)

Interaction Rating = Moderate Be cautious with this combination.

Talk to your health provider.

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)

Interaction Rating = Moderate Be cautious with this combination.

Talk to your health provider.

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)

Interaction Rating = Moderate Be cautious with this combination.

Talk to your health provider.

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), and numerous others.

Medications for diabetes (Antidiabetes drugs)

Interaction Rating = Moderate Be cautious with this combination.

Talk to your health provider.

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)

Interaction Rating = Moderate Be cautious with this combination.

Talk to your health provider.

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-transporting polypeptide substrates)

Interaction Rating = Moderate Be cautious with this combination.

Talk to your health provider.

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)

Interaction Rating = Moderate Be cautious with this combination.

Talk to your health provider.

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, and others.

Midazolam (Versed)

Interaction Rating = Moderate Be cautious with this combination.

Talk to your health provider.

Quercetin might increase how quickly the body breaks down midazolam . Taking quercetin with midazolam might reduce the effects of midazolam.

Pravastatin

Interaction Rating = Moderate Be cautious with this combination.

Talk to your health provider.

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.

Warfarin (Coumadin)

Interaction Rating = Moderate Be cautious with this combination.

Talk to your health provider.

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 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.

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.

There are no known interactions with foods.

The following dose has been studied in scientific research:

BY MOUTH:

  • For prostate pain and swelling (prostatitis): 500 mg twice daily.

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.


 

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