Poor digestive function does not usually lead to black stools, mostly due to dietary factors, medication factors, upper gastrointestinal bleeding, etc. 1. Dietary factors: Eating black food, such as black sesame, black beans, black fungus, or eating animal blood products, such as chicken blood, duck blood, etc., will cause black stools, stop eating these foods, can gradually return to normal. 2. Drug factors: taking iron supplements such as ferrous succinate, bismuth such as bismuth potassium citrate, etc., resulting in black stools. 3. Gastrointestinal bleeding: for example, bleeding caused by chronic gastritis, gastric ulcer, duodenal ulcer, etc. Because of the small amount of bleeding, the blood stays in the intestines for a long time, and after oxidation, black sulfide is formed, which causes black stools. If you exclude dietary and medication factors, you need to be alert to the presence of gastrointestinal bleeding, and it is recommended that you seek medical attention as soon as possible to identify the cause of the disease and follow the doctor’s instructions for treatment.