The first and only FDA approved prescription for male pattern hair loss is Propecia. It works to treat thinning hair on the vertex, (top of the head) and anterior (mid-scalp area) in men. Only diagnosed for men, one tablet is usually prescribed by a physician, daily. The benefits and results of Propecia are noticeable within 3 months. As soon as Propecia treatment is stopped, any gain in hair quantity is lost. The possible side effects that might occur with Propecia include impotence or a decreased sex drive. When Propecia is crushed, it must not be handled by women who are pregnant.