Orally, quercetin is used for atherosclerosis, hypercholesterolemia, hypertension, coronary heart disease, vascular insufficiency, diabetes, cataracts, allergic rhinitis, peptic ulcers, aphthous ulcers, schizophrenia, inflammation, rheumatoid arthritis (RA), niacin flush, asthma, gout, viral infections, bladder disorders and infections, chronic fatigue syndrome (CFS), preventing cancer, oral mucositis, treating prostatitis, improving hormone levels in women with polycystic ovary syndrome, and improving function of kidney transplants. It is also used to increase exercise endurance and improve athletic performance.