Finasteride

Finasteride is a 5-alpha-reductase inhibitor that reduces the conversion of testosterone into dihydrotestosterone (DHT) — a more potent androgen that contributes to male pattern baldness (androgenic alopecia), prostate enlargement, and potentially skin and scalp oiliness. It is commonly used in both medical and performance-enhancing contexts to help prevent or slow hair loss in genetically susceptible individuals, especially during steroid cycles that raise androgen levels.
Finasteride is most effective against DHT-related hair loss on the crown and mid-scalp, but less effective for receding hairlines or temple thinning.