Dutasteride is a 5-α-reductase inhibitor that inhibits the conversion of testosterone into dihydrotestosterone (DHT). Dutasteride inhibits both isoforms of 5-α reductase (5 α-Reductase 1/5aR1 and 5 α-Reductase 2/5aR2) to a similar extent (IC50 6nmol/l and 7 nmol/l, respectively), while finasteride only inhibits Type II. Dutasteride competed for binding the LNCaP cell AR with an IC50 approximately 1.5 μM. Dutasteride is a dual 5-α reductase inhibitor that inhibits conversion of testosterone to dihydrotestosterone (DHT).