Quercetin is one of a number of water-soluble plant pigments called bioflavonoids. Quercetin and the other bioflavonoids cannot be produced in the human body. They have been researched for a number of beneficial effects.

Quercetin is found in many foods including apples, onions, tea, berries, grapes, broccoli, cauliflower, and cabbage, as well as many seeds and nuts.

Dosage Info

Dosage Range

200-400mg, 2 to 3 times daily.

Most Common Dosage

400mg daily.

Dosage Forms

Tablets and capsules.

Reported Uses

Researchers think that quercetin may inhibit a number of substances that are responsible for producing symptoms of allergy and inflammation. (1) , (2) , (3) Quercetin may support the health of capillaries by enhancing their strength and permeability. (4) It may also function as an antiviral agent. (5) Studies have found that quercetin exhibited anticancer effects. (6) , (7) , (8)

Because quercetin is also an antioxidant, it can help prevent the oxidation or damage to cholesterol, (9) thereby reducing the risk of developing atherosclerosis. (10) Quercetin may also lower blood pressure by exhibiting coronary vasorelaxation properties. (11) , (12) This antioxidant activity may carry over to the treatment of cataracts and support of healthy vision. Studies suggest that quercetin may limit free radical damage to the eyes while inhibiting other factors that can damage vision. (13) , (14)

Toxicities & Precautions


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This dietary supplement is considered safe when used in accordance with proper dosing guidelines.

Pregnancy / Breast Feeding

To date, the medical literature has not reported any adverse effects related to fetal development during pregnancy or to infants who are breast-fed. Yet little is known about the use of this dietary supplement while pregnant or breast-feeding. Therefore, it is recommended that you inform your healthcare practitioner of any dietary supplements you are using while pregnant or breast-feeding.

Age Limitations

To date, the medical literature has not reported any adverse effects specifically related to the use of this dietary supplement in children. Since young children may have undiagnosed allergies or medical conditions, this dietary supplement should not be used in children under 10 years of age unless recommended by a physician.


  1. View Abstract: Bronner C, Landry Y. Kinetics of the Inhibitory Effect of Flavonoids on Histamine Secretion from Mast Cells. Agents Actions. 1985;16:147-51.
  2. View Abstract: Loggia Della, et al. Anti-inflammatory Activity of Benzopyrones that are Inhibitors of Cyclo- and Lipo-oxygenase. Pharmacol Res Commun. 1988;20:S91-S94.
  3. View Abstract: Wadsworth TL, McDonald TL, Koop DR. Effects of Ginkgo biloba extract (EGb 761) and quercetin on lipopolysaccharide-induced signaling pathways involved in the release of tumor necrosis factor-alpha. Biochem Pharmacol. Oct2001;62(7):963-74.
  4. Hertog MG, Hollman PC. Potential health effects of the dietary flavonol quercetin. Eur J Clin Nutr. Feb1996;50(2):63-71.
  5. View Abstract: Kaul TN, Middleton E Jr, Ogra PL. Antiviral effect of flavonoids on human viruses. J Med Virol. Jan1985;15(1):71-9.
  6. View Abstract: Morrow DM, Fitzsimmons PE, Chopra M, McGlynn H. Dietary supplementation with the anti-tumour promoter quercetin: its effects on matrix metalloproteinase gene regulation. Mutat Res. Sep2001;480-481:269-76.
  7. View Abstract: Mori H, Niwa K, Zheng Q, et al. Cell proliferation in cancer prevention; effects of preventive agents on estrogen-related endometrial carcinogenesis model and on an in vitro model in human colorectal cells. Mutat Res. Sep2001;480-481:201-7.
  8. View Abstract: Van Erk MJ, Roepman P, Van Der Lende TR, et al. Integrated assessment by multiple gene expression analysis of quercetin bioactivity on anticancer-related mechanisms in colon cancer cells in vitro. Eur J Nutr. Apr2004;:1-14.
  9. View Abstract: O'Reilly JD, Sanders TA, Wiseman H. Flavonoids protect against oxidative damage to LDL in vitro: use in selection of a flavonoid rich diet and relevance to LDL oxidation resistance ex vivo? Free Radic Res. Oct2000;33(4):419-26.
  10. View Abstract: Negre-Salvayre A, et al. Quercetin Prevents the Cytotoxicity of Oxidized LDL on Lymphoid Cell Lines. Free Radic Biol Med. 1992;12(2):101-06.
  11. View Abstract: Rendig SV, Symons JD. Effects of red wine, alcohol, and quercetin on coronary resistance and conductance arteries. J Cardiovasc Pharmacol. Aug2001;38(2):219-27.
  12. View Abstract: Duarte J, Galisteo M, Ocete MA, et al. Effects of chronic quercetin treatment on hepatic oxidative status of spontaneously hypertensive rats. Mol Cell Biochem. May2001;221(1-2):155-60.
  13. Beyer-Mears A, et al. Diminished Sugar Cataractogenesis by Quercetin. Exp Eye Res. Jun1979;28(6): 709-16.
  14. View Abstract: Chaudry PS, et al. Inhibition of Human Lens Aldose Reductase by Flavonoids, Sulindac, and Indomethacin. Biochem Pharmacol. 1983;32:1995-98.