5-alpha-reductase inhibitors are used to treat benign prostatic hyperplasia (BPH) and male-pattern hair loss. These medications work by blocking the enzyme 5-alpha-reductase, which helps to reduce the levels of dihydrotestosterone (DHT) in your body. Lowering DHT levels can help shrink an enlarged prostate and reduce hair loss. These medications are available in oral forms. Examples include finasteride (Propecia, Proscar) and dutasteride (Avodart).