Hair loss pills. Packet of Propecia hair loss pills that contain the drug finasteride, which acts to block the formation of the hormone dehydroxytestosterone (DHT). It is thought that DHT causes hair loss in men. Propecia has been shown to slow or halt male pattern hair loss (androgenetic alopecia) and in some cases caused regrowth. It is only intended for hair loss from the top of the head, not a receding hairline. Pregnant women must avoid the drug, as it may cause abnormalities in a male baby's sex organs. Larger amounts of finasteride are used for shrinking an enlarged prostate gland. Propecia is manufactured by Merck Sharp & Dohme.