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Epimedium is also known as Rowdy Lamb Herb, Barrenwort, Bishop's Hat, Fairy Wings, Horny Goat Weed, or Yin Yang Huo.

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, tablet, or capsule 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. Other research has demonstrated that injections of Epimedium extract directly into the penis of the rat results in an increase in penile blood pressure.

Like sildenafil (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 sildenafil has an IC50 of about 6.6 nanomolar (.0066 micromolar) and vardenafil (Levitra) has an IC50 of about 0.7 nanomolar (.0007 micromolar). Measured differently, the EC50 of icariin is approximately 4.62 micromolar, while sildenafil's is .42 micromolar. The amount of oral administration of Epidemium extract necessary to achieve these relative concentrations is unclear from the literature.

A recently published Italian study modified icariin structurally and investigated a number of derivatives.[10] Inhibitory concentrations for PDE-5 close to sildenafil could be reached. Moreover, the most potent PDE-5 inhibitor of this series was also found to be a less potent inhibitor of phosphodiesterase-6 (PDE-6) and cyclic adenosine monophosphate-phosphodiesterase (cAMP-PDE), thus showing it to have more specificity for PDE-5 than sildenafil.

Epimedium has been shown to up-regulate genes associated with nitric oxide production and changes in adenosine/guanine monophosphate balance in ways that other PDE5 inhibitors do not.

In regards to medicinal uses in women, a study* tested the estrogenic activity of 32 herbs used for menopause and Epimedium had some of the most potent estrogenic activity.

*Zhang CZ et al. In vitro estrogenic activities of Chinese medicinal plants traditionally used for the management of menopausal symptoms. Journal of Ethnopharmacology. 98.3 (2005):295-300.





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