Propecia (finasteride) is an oral medication used primarily for the treatment of male pattern baldness. When finasteride is marketed as Proscar, it is intended as treatment for benign prostatic hyperplasia (BPH; an enlarged prostate). It helps reduce the likelihood of getting a urinary tract infection or possibly needing prostate surgery. It is part of a class of medications called 5-alpha reductase inhibitors, and works by preventing the conversion of the hormone testosterone into dihydrotestosterone.