Thanks for contacting healthcare magic. According to your complain you have black stool problem that may be because of bleeding from digestive tract... Peptic ulcer or other problem may cause black stool means Melanie.... As soon as possible consent your physical for further diagnosis. Stool examination test help in diagnosis. .. Iron supplements may cause black stool... Proper physical examination and history give exact idea about disease. . I hope my guidance is helpful to you. Take care. Thanks.