How it works
Finasteride blocks an enzyme called type II 5α-reductase. That lowers DHT in the blood and scalp by ~70%. With less DHT, hair follicles shrink more slowly in androgenetic alopecia (pattern hair loss).
The evidence
Long-term trials (1–10 years) of 1 mg daily show more hairs and slower hair loss than placebo. This is especially true at the crown (the top and back of the head). Adding topical minoxidil adds to the effect.
Typical dosing
1 mg by mouth, once a day. Results show up over 3–6 months. To keep the results, you have to keep taking it.
Side effects
Common
- Lower sex drive
- Erection changes
Less common
- Mood changes
Rare
- Post-finasteride syndrome (debated, still being studied)
Drug interactions
- Generally few at low doses
