Food safety In 2010, the FDA acknowledged high-purity quercetin as GRAS for use as an ingredient in various specified food categories at levels up to 500 milligrams per serving. Health claims Quercetin has been studied in basic research and small clinical trials. While supplements have been promoted for the treatment of cancer and various other diseases, there is no high-quality evidence that quercetin (via supplements or in food) is useful to treat cancer or any other disease. The US Food and Drug Administration has issued warning letters to several manufacturers advertising on their product labels and websites that quercetin product(s) can be used to treat diseases. The FDA regards such quercetin advertising and products as unapproved – with unauthorized health claims concerning the anti-disease products – as defined by "sections 201(g)(1)(B) and/or 201 (g)(1)(C) of the Act [21 U.S.C. § 321(g)(1)(B) and/or 21 U.S.C. § 321(g)(1)(C)] because they are intended for use in the diagnosis, cure, mitigation, treatment, or prevention of disease", conditions not met by the manufacturers. Safety There has been little research into the safety of quercetin supplementation in humans, and the results are insufficient to give confidence that the practice is safe. In particular, there is a lack of safety information on the effect of quercetin supplementation for pregnant women, breastfeeding women, children, and adolescents. The hormonal effects of quercetin found in animal studies raise the suspicion of a parallel effect in humans, particularly in respect of estrogen-dependent tumors. Quercetin supplementation can interfere with the effects of medications. The precise nature of this interaction is known for some common medicines, but for many, it is not. See also List of ineffective cancer treatments Flavonol 3-sulfotransferase Phenolic compounds in wine Phytochemical Quercetin 2,3-dioxygenase Quercetin 3-O-methyltransferase Quercetin-3-sulfate 3'-sulfotransferase Quercetin-3-sulfate 4'-sulfotransferase Quercetin-3,3'-bissulfate 7-sulfotransferase References External links Aromatase inhibitors CYP2C8 inhibitors CYP3A4 inhibitors Flavonoid antioxidants GPER agonists Xanthine oxidase inhibitors Experimental medical treatments Phytoestrogens Selective ERβ agonists