Propecia (finasteride) is a compound developed by Merck & Co Inc., to treat mild to moderate hair loss in men only. Propecia belongs to a group of medicines that selectively blocks an enzyme (known as 5-alpha reductase type 2), which intervenes in the regulation of the hair follicle. Propecia was developed to treat male pattern hair loss on the vertex, or top of the head, and the anterior mid scalp area, or the middle front of the head, in men only. So far there is not sufficient evidence to show that Propecia works for receding hair lines at the temples.

Merck & Co. Inc. researched the causes of hair loss in the development of Propecia, and it was found that there were common factors in men with androgenetic alopecia, or male pattern hair loss. It is widely understood that male pattern hair loss may be inherited from your family and can come from either side. Usually this begins with a receding hairline and can include slow balding of the crown. A key factor is a chemical called dihydrotestosterone, which is more commonly known as DHT. The balding scalp contains miniaturized hair follicles and increased amounts of DHT compared with a hairy scalp. Propecia acts to inhibit this enzyme which is know to intervene in the regulation of the hair follicle.

Propecia was developed as a treatment for hair loss in men. Women cannot use Propecia due to the risk of pregnancy and it is unsuitable for children. Each tablet is coated to prevent contact with the ingredient during normal handling, but women must not handle crushed or broken Propecia tablets if they are pregnant or may become pregnant.