Finasteride, which is sold under the brand name Propecia, is a treatment for male pattern baldness. This is a genetic condition that causes testosterone to be converted into another hormone called dihydrotestosterone (DHT). DHT has a damaging effect on follicles and it can slow or stop the production of hair. Finasteride works by preventing the conversion of testosterone into DHT, helping to stop or reverse the balding process. It is most effective in men with mild to moderate hair loss.