| Section2 = }}Quercetin quer·ce·tin (ˈkwər-sə-tən)'s a plant-derived flavonoid, specifically a flavonol, used as a nutritional supplement. The American Cancer Society says that while quercetin "has been promoted as being effective against a wide variety of diseases, including cancer," and "some early lab results appear promising, as of yet there's no reliable clinical evidence that quercetin can prevent or treat cancer in humans." In the amounts consumed in a hea… (More on Quercetin)