Propecia is a drug for benign prostatic hyperplasia and male pattern baldness. It is a type 2 5-reductase inhibitor 5-reductase. It turns androgen testosterone into 5-dihydrotestosterone or DHT. Propecia blocks the male hormone that causes prostate enlargement. It treats male pattern baldness by obstructing the body's production of the male hormone, responsible for hair growth stoppage.