Androgenetic alopecia (AGA) is the most common type of hair loss and occurs in both men and women. In AGA, 5α-reductase enzymes convert testosterone to dihydrotestosterone (DHT), a potent metabolite of testosterone. DHT binds to androgen receptors with a five-fold greater affinity than testosterone, activating genes responsible for the gradual transformation of large terminal follicles to small, miniaturized follicles. Dutasteride inhibits both type 1 and 2 5α-reductase enzymes and has a potent ability of reducing scalp DHT was approved by the FDA in 2002 for the treatment of benign prostatic hyperplasia. Dutasteride is KFDA approved for the treatment of AGA. Phase II studies in AGA demonstrated a dose-dependent increase in hair growth. Twin studies showed that 0.5 mg dutasteride a day resulted in significantly more hair growth than placebo. When we compare with finasteride with dutasteride, dutasteride is three times more potent for inhibiting type 2 5α-reductase enzyme and 100 times more potent for inhibiting the type 1 enzyme in vitro. All dutasteride doses tested (0.05, 0.1, 0.5, 2.5 mg) and finasteride 5 mg were significantly better than placebo at 12 and 24 weeks, but only dutasteride at a 2.5 mg daily dose was statistically superior to finasteride with respect to hair counts. Recently published data showed the effectiveness of dutasteride at 0.02, 0.1 or 0.5mg daily and finasteride 1mg daily. At 24 weeks, dutasteride 0.5mg had significantly higher hair count and width, and improved hair growth compared with finasteride and placebo. There are no studies investigating the effect of dutasteride combined with minoxidil. In this session, updated knowledge on the dutasteride will be discussed.