How it works
Finasteride inhibits type II 5α-reductase, reducing serum and scalp DHT by ~70%. Lower DHT slows the miniaturization of hair follicles in androgenetic alopecia.
The evidence
Long-term trials (1–10 years) show improved hair counts and slowed progression vs. placebo at 1 mg daily, particularly in crown and vertex. Combined with topical minoxidil for additive effect.
Typical dosing
1 mg orally daily. Effects emerge over 3–6 months; durable response requires continued use.
Side effects
Common
- Decreased libido
- Erectile changes (reversible in most)
Less common
- Mood changes
Rare
- Post-finasteride syndrome (controversial, ongoing study)
Drug interactions
- Generally minimal at low doses