Final answer:
Finasteride is a medication used to treat male pattern hair loss by inhibiting the enzyme responsible for producing a hormone that contributes to hair loss.
Step-by-step explanation:
Finasteride is a 5-alpha-reductase inhibitor, which means it inhibits the enzyme responsible for converting testosterone to dihydrotestosterone (DHT). DHT is a hormone that contributes to male pattern hair loss. By reducing DHT levels, finasteride helps treat male pattern hair loss and can promote hair growth.