Demeclocycline is a semisynthetic tetracycline derived from Streptococcus aureofaciens that is used as an antibiotic, but perhaps more frequently as an inhibitor of arginine vasopressin in the therapy of hyponatremia and the syndrome of inappropriate secretion of antidiuretic hormone (SIADH). While demeclocycline has not been linked specifically to liver injury in the published literature, it is an orally available semisynthetic tetracycline and is likely to cause injury similar to that described for tetracycline, oxytetracycline, and doxycycline. Because it is not commonly used, its potential for causing liver injury may not have been fully defined.