Blocks the 5-alpha-reductase enzyme, and thereby inhibits conversion of testosterone to DHT. At a dose of 1 mg/day, finasteride lowers serum and scalp DHT levels by more than 60 percent. The drug does not interfere with testosterone action. After 6 or 12 months of treatment, hair count was 9% higher in patients treated with finasteride. compared with placebo. After 48 months of therapy, hair count was 24% higher. The recommended dose of finasteride is 1 mg per day. Hair regrowth will be lost over six to nine months if finasteride is discontinued.