Finasteride inhibits 5-alpha-reductase type II, the enzyme converting testosterone to dihydrotestosterone (DHT) in scalp follicles and prostate. At 1 mg daily, the Propecia dose, it reduces serum DHT approximately 70% and scalp tissue DHT about 60%, slowing miniaturization in androgenetic alopecia.
Clinical evidence
Two-year placebo-controlled trials in men aged 18 to 41 demonstrated increased hair counts, improved patient and investigator ratings, and slowed hair loss progression. Five-year extensions confirmed maintained benefit while on drug. Finasteride is FDA-approved for male pattern hair loss; 5 mg (Proscar) is for benign prostatic hyperplasia and must not be split casually due to coating inconsistencies in some generics.
Side effects in context
Phase 3 trials reported sexual adverse events (decreased libido, erectile dysfunction, ejaculation disorder) in 2 to 4% versus 2% placebo, a small but real differential that drives interest in topical finasteride alternatives. Post-marketing reports of persistent symptoms exist but epidemiologic incidence is debated. Men attempting conception should avoid finasteride due to potential semen drug exposure and theoretical fetal risk.
Combination with minoxidil
Oral finasteride plus topical minoxidil is standard combination dermatology for men who want maximum medical therapy. Mechanisms are complementary: DHT blockade plus growth-phase extension. Compounded hair sprays that include topical finasteride aim for similar DHT suppression with lower systemic exposure, covered in our men's quad-stack article.
CLYR Health offers finasteride 1mg oral capsules as a preview SKU for men whose providers determine systemic DHT blockade is appropriate.