Finasteride, sold under the brand names Proscar and Propecia among others, is a medication used mainly to treat an enlarged prostate or hair loss in men. It can also be used to treat excessive hair growth in women and as a part of hormone therapy for transgender women. It is taken by mouth.
Side effects are generally mild. Some men experience sexual dysfunction, depression, anxiety, or breast enlargement. It may also increase the risk of certain forms of prostate cancer. Finasteride is a 5α-reductase inhibitor, and therefore an antiandrogen. It works by decreasing the production of dihydrotestosterone (DHT) by about 70%, including in the prostate gland and the scalp.
Finasteride was patented in 1984 and approved for medical use in 1992. It is available as a generic medication. A month supply in the United Kingdom costs the NHS about 0.89 £ per month as of 2019. In the United States the wholesale cost of this amount is about 2.34 USD. In 2016 it was the 75th most prescribed medication in the United States with more than 10 million prescriptions.