Icariin is a flavonol, a type of flavonoid. It is the prenyl acetylation of kaempferide 3,7-O-diglycoside. The compound is derived from several species of plants in the Epimedium family, which are commonly known as Horny Goat Weed or Yin Yang Huo. Extracts from these plants are reputed to produce aphrodisiac effects, and are commonly used in Chinese herbal medicine to enhance erectile function, as well as for several other indications.

It is thought that icariin is likely to be the primary 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 and improve sexual function. In particular, icariin has been demonstrated to act as a PDE5 inhibitor and to enhance the production of bioactive nitric oxide, as well as mimicing the effects of testosterone. It also shows antioxidant, antidepressant and nootropic effects in animal studies, as well as stimulating osteoblast activity in bone tissue which has been linked to a possible therapeutic role in the treatment of osteoporosis.

he effect of icariin on the bone resorption activity of rabbit osteoclasts is assessed in vitro. Osteoclasts were isolated from Japanese white rabbits and cultured on plates with a sterilized bone slice in each well. After treatment with icariin at various concentrations, the bone resorption activity of osteoclasts was evaluated by examining pit areas, superoxide anion (·O 2 − ) generation, size and number of actin rings and intracellular calcium concentration [Ca2+]i. As revealed by these data, icariin elicited continuous decline of [Ca2+]i, making actin ring constricted and ·O2 − generation decreased. These events resulted in smaller and fewer pits which indicate suppressed bone resorption activity of rabbit osteoclasts by icariin.