Preliminary evidence suggests that it may modulate levels of the hormones cortisol, testosterone, and thyroid hormone, bringing low levels back to normal.

Animal studies indicate that horny goat weed may work by increasing nitric oxide levels, which relaxes smooth muscle allowing an increased blood flow to the penis or clitoris.  Horny goat weed may also inhibit the PDE-5 enzyme (cGMP-specific phosphodiesterase type 5).  The PDE-5 enzyme has a degrading effect on the smooth muscle cells lining the blood vessels supplying the corpus cavernosum of the penis.  PDE-5 inhibitors are used in the treatment of erectile dysfunction.

Horny Goat Weed contains flavonol glycosides, including icariin.  Icariin can block an erection-inhibiting enzyme but without the side effects.