What it is
A synthetic 4-azasteroid 5-alpha-reductase inhibitor available as oral tablets. Also available in compounded topical formulations.
How it works
Selectively inhibits the type II isoform of 5-alpha-reductase, the enzyme that converts testosterone to dihydrotestosterone (DHT), lowering scalp and serum DHT.
Where it's used
Used in male pattern hair loss (androgenetic alopecia) and benign prostatic hyperplasia.
FDA-approved use
Male pattern hair loss (Propecia, 1 mg); benign prostatic hyperplasia (Proscar, 5 mg). Topical formulations are not FDA-approved.
Tracking it
Finasteride is oral, which makes consistency the whole game — a simple daily check-off with a reminder beats memory every time. with a half-life of about 6 hours, a dose log also lets a tracker model the relative amount still in your system between doses.
Source
OpenFDA
Last reviewed 2026-06-11