An aza-steroid that is inasteride in which the tert-butyl group is replaced by a 2,5-bis(trifluoromethyl)phenyl group. A synthetic 4-azasteroid, dutasteride is a selective inhibitor of both the type 1 and type 2 isoforms of steroid 5alpha-reductase, an intracellular enzyme that converts testosterone to 5alpha-dihydrotestosterone. Dutasteride is used for the treatment of symptomatic benign prostatic hyperplasia in men with an enlarged prostate gland.