Icariin is a chemical compound classified as a flavonol glycoside, a type of flavonoid. It is the 8-prenyl derivative of kaempferol 3,7-O-diglucoside. The compound has been isolated from several species of plants belonging to the genus Epimedium which are commonly known as Horny Goat Weed or Yin Yang Huo. Extracts from these plants are reputed to produce aphrodisiac effects, and are used in traditional Chinese medicine to enhance erectile function.
It is thought that icariin is an active component of Epimedium extracts, as it has been shown to share several mechanisms of action with compounds used in Western medicine to treat impotence. In particular, icariin is a weak PDE5 inhibitor in vitro and enhances the production of nitric oxide, as well as mimicking the effects of testosterone in rats.[unreliable medical source?] It is a weak antioxidant and has antidepressant-like effects in mice. It also has neuroprotective effects in rats.