Icariin

The flavonoid compound in Horny Goat Weed thought to be responsible for its aphrodisiac effects.  Icariin is a phosphodiesterase-5 (PDE-5) inhibitor, and may act as a sort of “herbal Viagra” to enhance/maintain erectile function.  Cell culture and animal experiments have shown icariin is biologically active, and also has anti-osteoporotic, neuroprotective and antioxidant activities.