Proscar (finasteride) is an FDA-approved prescription medication used to treat benign prostatic hyperplasia (BPH) in men. It works by inhibiting the enzyme 5-alpha-reductase, which reduces the conversion of testosterone to dihydrotestosterone (DHT). Lowering DHT levels helps shrink an enlarged prostate, improve urinary flow, and reduce symptoms such as difficulty starting urination, weak stream, and the need to urinate frequently or urgently. Proscar may also reduce the risk of acute urinary retention and the need for prostate surgery when taken long-term. It is available in tablet form for once-daily use and is not approved for the treatment of prostate cancer or for use in women or children.