Finasteride is a medication primarily used to treat male pattern hair loss by blocking the activity of the enzyme 5-alpha reductase, specifically the type II isoenzyme. This enzyme converts testosterone into dihydrotestosterone (DHT), a hormone that shrinks hair follicles and leads to hair thinning and loss. By inhibiting 5-alpha reductase, finasteride reduces scalp and serum DHT levels by about 60-70%, helping to prevent further hair loss and promoting hair regrowth in many men. The medication is taken orally, typically in a 1 mg daily dose, and is effective when used continuously. It is not recommended for use by women who are or may become pregnant due to potential risks to the fetus. Finasteride is often used in combination with minoxidil for enhanced results in managing androgenetic alopecia.