Finasteride is an antiandrogen which acts by inhibing 5-alpha reductase, the enzyme the converts testosterone to dihydrotestosterone. It is used in benign prostatic hyperplasia (BPH) in low doses, and in prostate cancer in higher doses. Additionally, it is registered in many countries for male-pattern baldness. Drug trade names include Propecia ® and Proscar ® both products of Merck & Co. (the former is marketed for hair loss in male pattern baldness, and the latter for BPH).