I pulled this directly off of Wikipedia.

In herbal medicine, damiana is used to treat conditions ranging from coughs to constipation to depression. The herbal supplement is reputed to help with energy, emphysema, low estrogen, frigidity, hot flashes, impotency, infertility, menopause, Parkinson's disease, PMS, inflammation of prostate, Lou Gehrig's disease, and more dealing with reproductive organs in both males and females. Damiana can also be made into a liquor. A traditional Mexican liquor, it is sometimes used in margaritas. Mexican folklore claims that it was used in the first margarita. This particular drink is popular in the Los Cabos region of Mexico. (The bottle of my favorite brand in shaped like the torso of a voluptuous woman.)