Find out how finasteride treats benign prostate enlargement and hair loss in men, and how to take it. NHS medicines information on finasteride – what it's used for, side effects, dosage and who can take it. Finasteride works by reducing the amount of DHT available by blocking an enzyme called 5α-reductase, which converts testosterone into DHT. Lower levels of DHT help improve hair growth in male pattern hair loss and reduce symptoms of BPH. 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. Learn about the side effects of finasteride, from common to rare, for consumers and healthcare professionals. 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 (Proscar, Propecia) is used to treat male pattern hair loss or benign prostatic hyperplasia. Learn about side effects, warnings, dosage, and more. 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. Finasteride (Propecia, Proscar) is a medication used to treat benign prostatic hyperplasia (BPH) and male-pattern hair loss. It’s more likely to cause side effects at the higher dosage (5 mg) used to treat BPH. Common finasteride side effects include erectile dysfunction and decreased sex drive. What Is Finasteride and How Does It Work? 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 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.