Propecia (Finasteride) is a medication classified as a 5-alpha-reductase inhibitor. It works by inhibiting the enzyme responsible for converting testosterone into dihydrotestosterone (DHT), a hormone that contributes to the enlargement of the prostate gland. Propecia is primarily used to treat male pattern hair loss (androgenetic alopecia) in men. By reducing DHT levels in the scalp, Propecia helps to slow hair loss and promote hair regrowth. Clinical studies have shown that Propecia can lead to increased hair count, improved hair growth, and a delay in the progression of hair loss. It may take several months of continuous use to see noticeable effects.