Cimetidine (CMT)

Cimetidine is a histamine H2-receptor antagonist that inhibits stomach acid production. Cimetidine's mechanism of action is as an H2 receptor antagonist. Cimetidine has also been found to possess clinically significant anti-androgen properties at high doses that are especially noticeable in men. It directly antagonizes the binding of testosterone and DHT to the androgen receptor in animals. In addition, also in animals, it interferes with the metabolism of estrogen and increases its serum concentrations. Accordingly, cimetidine has been found to be effective in small clinical trials for the treatment of acne and androgenic alopecia, though not in hirsutism or in sex hormone-associated cancers such as breast and prostate cancer. Cimetidine's anti-androgen properties likely explain certain side effects seen with it such as galactorrhea and amenorrhea in women and gynecomastia and impotence in men.