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A 5-alpha-reductase inhibitor that lowers scalp DHT to slow hair loss; FDA-approved for male pattern loss.
Finasteride is an oral (and increasingly topical) drug that blocks 5-alpha-reductase, cutting DHT and thereby slowing follicle miniaturization and partially regrowing hair. It is FDA-approved for male androgenetic alopecia at 1 mg/day and requires continued use to maintain results. A minority of men report sexual side effects; it is not used in women who may become pregnant.