Upon maturation, these individuals were observed to have smaller prostates which were underdeveloped, and were also observed to lack incidence of male pattern baldness.In 1975, copies of Imperato-McGinleys presentation were seen by P. Roy Vagelos, who was then serving as Mercks basic-research chief. He was intrigued by the notion that decreased levels of DHT led to the development of smaller prostates. Dr. Vagelos then sought to create a drug which could mimic the condition found in these children to treat older men who had  benign prostatic hyperplasia.Finasteride was developed by Merck under the code name MK-906. A team led by chemist Gary Rasmusson and biologist Jerry Brooks developed potential 5α-reductase inhibitors based on transition state inhibitors, using an iterative process of molecular design, testing, and redesign. In 1992, finasteride (5 mg) was approved by the U.S. Food and Drug Administration (FDA) for treatment of BPH, which Merck marketed under the brand name Proscar. Rasmusson and Brooks were awarded IPOs "Inventor of the Year" award in 1993 for their work on finasteride. In 1997, Merck was successful in obtaining FDA approval for a second indication of finasteride (1 mg) for treatment of male pattern hair loss, which was marketed under the brand name Propecia. It was the first 5α-reductase inhibitor to be introduced and was followed by dutasteride in 2001. The first study of finasteride in the treatment of hirsutism in women was published in 1994.
Finasteride may improve the symptoms associated with BPH such as difficulty urinating, getting up during the night to urinate, hesitation at the start and end of urination, and decreased urinary flow. It provides less symptomatic relief than alpha-1 blockers such as tamsulosin and symptomatic relief is slower in onset (six months or more of treatment with finasteride may be required to determine the therapeutic results of treatment). Symptomatic benefits are mainly seen in those with prostate volume > 40 cm3. In long-term studies finasteride but not alpha-1 inhibitors reduce the risk of acute urinary retention (−57% at 4 years) and the need for surgery (−54% at 4 years). If the drug is discontinued, any therapeutic benefits are reversed within about 6–8 months. Scalp hair loss
Finasteride is also used to treat male pattern baldness (androgenic alopecia) in men, a condition that develops in up to 80% of Caucasian men. In the United States, finasteride and minoxidil are the only two FDA approved drugs for the treatment of male pattern hair loss as of 2017. Treatment with finasteride slows further hair loss and provides about 30% improvement in hair loss after six months of treatment, with effectiveness persisting as long as the drug is taken. 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.