Propecia tablets contain the active ingredient, finasteride 1mg which is used to treat male pattern baldness (androgenic alopecia). Propecia is not used to treat hair loss in women.
Finasteride is in a class of medications known as 5α-reductase inhibitors. The enzyme, 5α-reductase has been associated with prostatic enlargement and hair loss. Blocking this enzyme prevents enlargement of the prostate gland and helps to slow hair loss in males.
5α-reductase converts the male hormone, testosterone to dihydrotestosterone (DHT). It is DHT that is responsible for causing hair follicles on the scalp to shrink and produce thinner and weaker hair. Blocking 5α-reductase helps to reverse the process and allow hair to grow normally.