Finasteride (Propecia) helps balding men grow hair, but it can cause sexual problems— according to an Argentinian study. Propecia works by preventing the conversion of testosterone to dehydrotestosterone, which is the hormone that promotes hair loss in aging men.
During a two-year study, the drug increased hair production by 30 percent but caused sexual problems, such as erectile dysfunction and decreased sex drive in some men. The study presents a dilemma: Propecia might make you more attractive to women, but you might not be able to do anything when you get them. (Archives of Dermatology, 146:1141-1150)