Horny goat weed as Viagra alternative

Researchers seeking natural "aphrodisiacs" as alternatives to Viagra think that the aptly-named horny goat weed may hold promise. According to University of Milan pharmacologist Mario Dell'Agil, a drug derived from the plant could potentially be as effective as Viagra without the same side effects as the little blue pill. From New Scientist:
Viagra's active compound, sildenafil, works by inhibiting an enzyme called phosphodiesterase-5 (PDE5). Because PDE5 helps control blood flow to the penis, inhibiting PDE5 promotes male erection.

Dell'Agli and his colleagues tested the four plants in vitro to see how efficient they were at inhibiting PDE5. Just one – Epimedium brevicornum, also known as horny goat weed and Bishop's Hat – had an effect. This confirmed previous studies showing that icariin, a compound found inside the horny goat weed, is a PDE5 inhibitor.
"Horny goat weed could be better than Viagra" (New Scientist)