Clostebol (INN), usually as the ester clostebol acetate, is a synthetic anabolic androgenic steroid. Clostebol is the 4-chloro derivative of the natural hormone testosterone. It is a weak anabolic steroid which was used by athletes from the German Democratic Republic (East Germany). It is a version of testosterone that is chlorinated so as to prevent conversion to DHT while also rendering the chemical incapable of conversion to estrogen.