Finasteride, <ref name="Finasteride"/> sold under the brand names Proscar and Propecia among others, is a medication used for the treatment of benign prostatic hyperplasia (enlarged prostate) and pattern hair loss.[1][2] It is a type II and type III 5α-reductase inhibitor;[3] 5α-reductase, an enzyme, converts testosterone to dihydrotestosterone (DHT).