Drinking black tea will not affect the color of stool. The darkening of stool color can be due to physiological and pathological reasons, which need to be consulted in time and judged under the guidance of a medical professional. Normal stools are yellowish brown and formed. Dark stool color can be divided into physiological causes and pathological causes. 1. Physiological reasons: taking certain drugs, such as ferrous sulfate, bismuth potassium citrate, etc.; consuming foods containing more iron, such as animal blood products, animal liver, etc.; eating foods with high pigment content, such as mulberries, spinach, seaweed and so on. All of these factors can lead to darker stool color. 2. Pathological reasons: digestive diseases such as gastric and duodenal ulcer, gastric mucosal bleeding, esophageal cancer, gastric cancer and so on can lead to darker stool color. The deepening of stool color caused by food and medication will usually return to normal within 1~2 days after stopping use, so there is no need to worry. If there is any unexplained deepening of stool color, it is better to go to regular hospitals for relevant examinations and clarify the cause of the disease under the guidance of professional physicians.