quercetin

Quercetin is a plant-derived compound known as flavonoid, the pigment that gives many flowers, fruits and vegetables their colors. Quercetin is widely available over the counter as oral formulations and is commonly taken as an herbal supplement. Quercetin is believed to have many health benefits due to its anticarcinogenic, antiviral, antioxidant and anti-inflammatory properties.

Quercetin is an antioxidant that scavenges free radicals and reduces tissue damage from oxidative stress, a major contributor to inflammation. Oxidative stress is caused by imbalance in the levels of free radicals and antioxidants that can neutralize them. Quercetin reduces inflammation by inhibiting the release of inflammatory substances such as histamine and cytokines. Quercetin also inhibits aldose reductase, an enzyme that plays a role in the breakdown of glucose.

The suggested uses of quercetin include:

• Asthma and allergies such as hay fever and hives
• Prevention of diabetic cataracts
• Viral infections
• Cardiovascular diseases including:
  • Hardening of the arteries (atherosclerosis)
  • High cholesterol
  • High blood pressure (hypertension)
• Adjunctive therapy in cancer
• Chronic prostate inflammation (prostatitis)
• Chronic bladder inflammation (interstitial cystitis)

There is insufficient evidence, however, for the efficacy of quercetin and it is not approved by the FDA for therapeutic purposes.

Dietary sources of Quercetin include apples, onions, citrus fruits, tea, sage, parsley, dark berries, grapes, red wine, and olive oil.

• High doses (greater than 1 g per day) of quercetin may cause kidney damage
• Avoid taking quercetin if you have kidney disease
• Avoid taking quercetin during pregnancy and nursing

Common side effects of quercetin include:

• Abnormal skin sensations (paresthesia)
• Headache
• Nausea and vomiting
• Shortness of breath (dyspnea)
• Toxicity to kidney (nephrotoxicity)

This is not a complete list of all side effects or adverse reactions that may occur from the use of this drug. Call your doctor for medical advice about serious side effects or adverse reactions. You may also report side effects or health problems to the FDA at 1-800-FDA-1088.

Adult

• 400-500 mg orally three times daily
• Prostatitis: 500 mg orally twice daily
• Cancer: 420-1400 mg/m2 intravenous (IV) bolus once/week

Pediatric

• There is insufficient evidence to recommend use in children

Inform your doctor of all medications you are currently taking, who can advise you on any possible drug interactions. Never begin taking, suddenly discontinue, or change the dosage of any medication without your doctor’s recommendation.

• Quercetin has no known severe interactions with other drugs.
• Serious Interactions of quercetin include:
  • everolimus
  • topotecan
• Quercetin has moderate interactions with at least 60 different drugs.
• Mild interactions of quercetin include:
  • alvimopan
  • armodafinil
  • ciprofloxacin
  • fexofenadine
  • fleroxacin
  • gemifloxacin
  • levofloxacin
  • loratadine
  • moxifloxacin
  • norfloxacin
  • ofloxacin

The drug interactions listed above are not all of the possible interactions or adverse effects. For more information on drug interactions, visit the RxList Drug Interaction Checker.

It is important to always tell your doctor, pharmacist, or health care provider of all prescription and over-the-counter medications you use, as well as the dosage for each, and keep a list of the information. Check with your doctor or health care provider if you have any questions about the medication.

• Little is known about quercetin use during pregnancy and breastfeeding; avoid use.

• 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.