Diarrhea with dark brown stools is usually not serious if it is caused by diet, medication, etc. However, it may be caused by gastrointestinal bleeding, which is serious if it is heavy and should be treated promptly. If you have recently consumed a lot of blood products, spinach or used iron supplements, these substances containing large amounts of iron can produce black ferrous sulfide under the action of gastric acid and intestinal flora, which can make the feces black in color. This is usually a less serious condition, and diarrhea can be treated with antidiarrheal medications such as montelukast under the direction of a doctor. Bleeding in the digestive tract can also cause iron containing blood to enter the digestive tract and produce ferrous sulfide, which usually produces black stools in upper gastrointestinal bleeding. This condition should be treated promptly in a gastroenterology department, where the cause of the GI bleeding can be observed under gastroscopy or colonoscopy, whether the bleeding stops and whether the bleeding stops. Commonly used medications include omeprazole and octreotide, and interventional or surgical hemostasis can also be performed. Diarrhea with dark brown color can be reviewed whether the recent consumption of blood products or certain iron-containing agents, if the duration is long or the color of the stool becomes darker should be promptly to the gastroenterology department, improve the examination, standardized treatment.