Horny goat weed is a genus of herbaceous flowering plants, native to southern China. Varieties and hybrids have been in Western cultivation for the last 100 to 150 years. Many species are alleged to have aphrodisiac qualities, and horny goat weed is now sold as a supplement, usually in raw herb, tablet, or capsule form and sometimes blended with other supplements. The "active ingredient" is icariin, and functions by increasing levels of nitric oxide, which relaxes smooth muscles and increase blood pressure. Horny goat weed is used to treat impotence and sexual dysfunction, as well as to alleviate menopausal symptoms.