Finasteride is one of the most extensively studied medications available for male androgenetic alopecia, commonly known as male pattern hair loss. It is a prescription 5 alpha reductase inhibitor that reduces the conversion of testosterone into dihydrotestosterone, or DHT. Learn about the side effects of finasteride, from common to rare, for consumers and healthcare professionals. Finasteride is from a class of medicines called 5α-reductase inhibitors. Finasteride 5mg tablets are used to treat symptomatic benign prostatic hyperplasia (BPH) in men, and finasteride 1mg tablets are used to treat male pattern hair loss in men. Finasteride explained: how it blocks DHT, 1 mg for hair loss and 5 mg for BPH, side effects, dosage, results, and how it compares to other treatments. Finasteride works by blocking an enzyme called 5-alpha-reductase Type II, which converts testosterone into dihydrotestosterone (DHT). DHT is the androgen primarily responsible for both male pattern hair loss and prostate growth. Finasteride is a prescription medication used to treat Benign Prostatic Hyperplasia and Androgenic Alopecia in males. Finasteride is available under the following different brand names: Propecia, Proscar. Finasteride is used to treat men who have symptoms of benign prostatic hyperplasia (BPH) and male pattern hair loss, also called androgenetic alopecia. BPH is caused by an enlarged prostate. Finasteride is in a class of medications called 5-alpha reductase inhibitors. Finasteride treats BPH by blocking the body's production of a male hormone that causes the prostate to enlarge. Taking finasteride leads to a reduction in scalp and serum DHT levels; by lowering scalp levels of DHT, finasteride can maintain or increase the amount of terminal hairs in the anagen phase by inhibiting and sometimes reversing miniaturization of the hair follicle. Finasteride is commonly used to treat BPH, which is non-cancerous enlargement of the prostate. In some people, BPH can occur at the same time as prostate cancer.