Approved by the FDA in 1997, Propecia (finasteride 1mg) is the first pill proven to treat genetic hair loss in the crown and mid-scalp area of men. In clinical trials, Propecia stopped hair loss in over 80% of cases and stimulated hair re-growth in around half of cases.

Male pattern hair loss is due to the effects of dihydrotestosterone (DHT) on genetically susceptible hair follicles. Finasteride works by inhibiting type II 5-alpha-reductase (the enzyme that produces DHT from testosterone). Therefore, by reducing DHT production, finasteride can prevent and even reverse the process of hair loss. Because of its mode of action, finasteride is not recommended for use by women.

Finasteride, at a low dose (1mg/day,) has few side effects and those that occur are resolved when the medication is stopped. One side effect, which occurs in up to 2% of men, is a change in sexual desire or function. Low dose finasteride does not affect sperm function or fertility and the medication presents no risk to women during normal sexual relations; however pregnant women and women of childbearing age should not take or handle the medication.