Finasteride
Propecia · 5α-reductase inhibitor (hair)
What it is
The standard prescription drug for male pattern hair loss — blocks conversion of testosterone to DHT, the androgen that miniaturises follicles. The most evidence-backed oral option for keeping hair, and the most argued-about because of persistent-side-effect reports.
What human evidence shows
Strong: decades of trials show it halts loss in the large majority and regrows some hair in many. DHT reduction ~70% at standard prescribing. Effect requires continuous use — stopping returns you to baseline trajectory within a year.
Risks
Sexual side effects (libido, erectile function) occur in a small percentage in trials; the contested part is post-finasteride syndrome — persistent symptoms after stopping, which regulators list while the literature fights over causality and rate. Mood effects reported. Crushed-tablet exposure is dangerous in pregnancy (topical/handling warning). Anyone running exogenous androgens changes this calculus entirely.
Legal status
US: prescription-only (not scheduled); telehealth prescribing is trivial to obtain.
Evidence base
established literature
Large human evidence base: several phase 3 or 4 trial reports, plus multiple meta-analyses or systematic reviews.
- phase 3/4
- 17
- randomised
- 356
- reviews
- 113
- human trials
- 468
Counts are of published papers, not distinct trials, and measure how much research exists — not whether this works or is safe for you.
Research (12)
- Comparison of oral minoxidil, finasteride, and dutasteride for treating androgenetic alopeciaJ Dermatolog Treat · 2022
- Finasteride for hair loss: a reviewJ Dermatolog Treat · 2022
- Efficacy and safety of topical finasteride spray solution for male androgenetic alopecia: a phase III, randomized, controlled clinical trialJ Eur Acad Dermatol Venereol · 2022
- Risk of Depression Associated With Finasteride TreatmentJ Clin Psychopharmacol · 2021
- Sexual side effects of 5-α-reductase inhibitors finasteride and dutasteride: A comprehensive reviewDermatol Online J · 2017
- Topical finasteride for male and female pattern hair loss: Is it a safe and effective alternative?J Cosmet Dermatol · 2022
- Post-Finasteride Syndrome. Literature ReviewArch Esp Urol · 2022
- Finasteride in the treatment of men with androgenetic alopecia. Finasteride Male Pattern Hair Loss Study GroupJ Am Acad Dermatol · 1998
- FinasterideExpert Opin Drug Metab Toxicol · 2010
- The effects of finasteride on scalp skin and serum androgen levels in men with androgenetic alopeciaJ Am Acad Dermatol · 1999
- Comparitive effectiveness of finasteride vs Serenoa repens in male androgenetic alopecia: a two-year studyInt J Immunopathol Pharmacol · 2012
- Finasteride and androgenic alopecia; from therapeutic options to medical implicationsJ Dermatolog Treat · 2020
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