Finasteride is a medication used to treat pattern hair loss and benign prostatic hyperplasia (BPH) in men. It can also be used to treat excessive hair growth in women.It is usually taken orally but there are topical formulations for patients with hair loss, designed to minimize systemic exposure by acting specifically on hair follicles.

Finasteride is a 5α-reductase inhibitor and therefore an antiandrogen.It works by decreasing the production of dihydrotestosterone (DHT) by about 70%.^[6]

In addition to DHT, finasteride also inhibits the production of several anticonvulsant neurosteroids including allopregnanolone, androstanediol, and tetrahydrodeoxycorticosterone.

Adverse effects from finasteride are rare in men with already enlarged prostates;however, some men experience sexual dysfunction, depression, and breast enlargement. In some men, sexual dysfunction may persist after stopping the medication. It may also hide the early symptoms of certain forms of prostate cancer.

Finasteride was patented in 1984 and approved for medical use in 1992. It is available as a generic medication. In 2023, it was the 91st most commonly prescribed medication in the United States, with more than 7 million prescriptions.