Horny Goat Weed

(Epimedium)

Epimedium is a genus of about 60 or more species of herbaceous flowering plants in the family Berberidaceae. The large majority are endemic to southern China, with further outposts in Europe, and central, southern and eastern Asia.

Epimedium species are hardy perennials. The majority have four petaled "spider-like" flowers in spring. Many are believed to be aphrodisiacs.

Many species of Epimedium are alleged to have aphrodisiac qualities. According to legend, this property was discovered by a Chinese goat herder who noticed sexual activity in his flock after they ate the weed. It is sold as a health supplement, usually in raw herb or pill form and sometimes blended with other supplements. The over-exploitation of wild populations of Epimedium for use in traditional Chinese medicine is having potentially serious consequences for the long-term survival of several species, none of which are widely cultivated for medicinal purposes.

The "active ingredient" in Epimedium is icariin, which can be found in standardized extracts from 5% up to 60% potent. Strengths above that are usually reserved for lab use.

Icariin is purported to work by increasing levels of nitric oxide, which relax smooth muscle. It has been demonstrated to relax rabbit penile tissue by nitric oxide and PDE-5 activity.

Like Viagra, icariin, the active compound in Epimedium, inhibits the activity of PDE-5. In vitro assays have demonstrated that icariin inhibits PDE-5 with an IC₅₀ of around 1 micromolar, while Viagra has an IC₅₀ of about 6.6 nanomolar (.0066 micromolar) and Levitra has an IC₅₀ of about 0.7 nanomolar (.0007 micromolar). Measured differently, the EC₅₀ of icariin is approximately 4.62 micromolar