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Quercetin is a plant pigment (flavonoid). It's found in many plants and foods, such as red wine, onions, green tea, apples, and berries.

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

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 no strong scientific evidence to support most of these uses. There is also no good evidence to support using quercetin for COVID-19.

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.
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When taken by mouth: Quercetin is possibly safe for most people when used short-term. Quercetin has been safely used in doses up to 1 gram daily for 12 weeks. It's not known if long-term use or higher doses are safe.

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.

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.

Herbs and supplements that might lower blood pressure: Quercetin might lower blood pressure. Taking it with other supplements that have the same effect might cause blood pressure to drop too much. Examples of supplements with this effect include andrographis, casein peptides, L-arginine, niacin, and stinging nettle.
Herbs and supplements that might lower blood sugar: Quercetin might lower blood sugar. Taking it with other supplements with similar effects might lower blood sugar too much. Examples of supplements with this effect include aloe, bitter melon, cassia cinnamon, chromium, and prickly pear cactus.

There are no known interactions with foods.

Quercetin has most often been used by adults in doses of 250-1000 mg by mouth daily for up to 12 weeks. Speak with a healthcare provider to find out what dose might be best for a specific condition.

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