Drinking black coffee usually does not lead to black stools, which may be caused by upper gastrointestinal bleeding, drug factors, malignant tumors and other reasons. Black coffee is made from coffee beans and contains caffeine, tannins and other substances, but it usually does not cause changes in stool traits or stool color. Other factors need to be considered: 1. Upper gastrointestinal bleeding: for example, gastric ulcer bleeding, duodenal ulcer bleeding, blood oxidized through the intestines to discharge black stool. 2. Drugs: taking bismuth (e.g. bismuth potassium citrate), iron supplements (ferrous succinate), etc. can appear black stools. 3. Malignant tumors: for example, stomach cancer, etc., due to the mucous membrane on the surface of the tumor erosion, oozing blood through the intestinal oxidation, black stools can occur. It is recommended to consult a doctor to find out the cause of the disease and treat it as soon as possible.