The appearance of dark brown stools may be physiological reasons such as eating more meat and animal liver substances, but also pathological reasons, such as upper gastrointestinal bleeding, intestinal tumors and so on. 1. Physiological reasons: may be some iron-containing drugs, food, such as polysaccharide iron capsule, duck blood, animal liver and so on. After taking iron ions in the gastrointestinal tract will be combined with hydrogen sulfide to form iron sulfide, the stool color is brown. 2. Pathologic causes: (1) Gastrointestinal bleeding: for example, when there are ulcers in the stomach, duodenum and other parts of the stomach, or long-term oral non-steroidal anti-inflammatory drugs without, etc. can cause bleeding in the gastrointestinal tract, the blood will be with the food, into the intestinal tract, and when the blood is oxidized in the intestines and discharged out of the body, black-brown stools will appear. (2) Intestinal tumor: If there is malignant tumor in the intestinal tract, such as the right half of the colon, it may lead to mucous membrane breakage and bleeding, which is manifested as dark brown stools with black color, and bloody stools can be seen when the bleeding volume is large. If you have dark brown stools with change of stool shape or other discomforts, it is recommended to consult a doctor in time, follow the doctor’s instructions for further examination, clarify the cause with the help of the doctor, and carry out targeted treatment or therapy.