Rutin, also called rutoside, quercetin-3-rutinoside and sophorin, is a citrus flavonoid glycoside found in buckwheat, the leaves and petioles of Rheum species, and the fruit of the Fava D'Anta tree (from Brazil), as well as other sources. Rutin is the glycoside between the flavonol quercetin and the disaccharide rutinose.

It can combine with cations, supplying nutrients from the soil to the cells in plants. In humans, it attaches to the iron ion Fe²⁺, preventing it from binding to hydrogen peroxide, which would otherwise create a highly-reactive free-radical that may damage cells. It is also an antioxidant, and therefore plays a role in inhibiting some cancers.

Rutin also strengthens the capillaries, and, therefore, can reduce the symptoms of haemophilia. It also may help to prevent a common unpleasant-looking venous edema of the legs. Rutin, as ferulic acid, can reduce the cytotoxicity of oxidized LDL cholesterol and lower the risk of heart disease.