Background: Data suggest that androgenetic alopecia is a process dependent on dihydrotestosterone (DHT) and type 2 5α-reductase. Finasteride is a type 2 5α-reductase inhibitor that has been shown to slow further hair loss and improve hair growth in men with androgenetic alopecia. Objective: We attempted to determine the effect of finasteride on scalp skin and serum androgens. Methods: Men with androgenetic alopecia (N = 249) underwent scalp biopsies before and after receiving 0.01, 0.05, 0.2, 1, or 5 mg daily of finasteride or placebo for 42 days. Results: Scalp skin DHT levels declined significantly by 13.0% with placebo and by 14.9%, 61.6%, 56.5%, 64.1%, and 69.4% with 0.01, 0.05, 0.2, 1, and 5 mg doses of finasteride, respectively. Serum DHT levels declined significantly (P < .001) by 49.5%, 68.6%, 71.4%, and 72.2% in the 0.05, 0.2, 1, and 5 mg finasteride treatment groups, respectively. Conclusion: In this study, doses of finasteride as low as 0.2 mg per day maximally decreased both scab skin and serum DHT levels. These data support the rationale used to conduct clinical trials in men with male pattern hair loss at doses of finasteride between 0.2 and 5 mg.
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