Black stools may be related to food, drugs, etc. In addition, gastrointestinal bleeding is also one of the important causes of black stools. 1. Food and drugs: Eating iron-containing food such as animal blood, iron-rich vegetables, taking iron and bismuth such as ferrous sulfate, ferric ammonium citrate, bismuth potassium citrate, bismuth pectin and other drugs, these foods and drugs in the digestive tract when passing through the stools can be blackened. 2. Gastrointestinal bleeding: Upper gastrointestinal bleeding can be manifested as black stools due to the upward location of the bleeding and the process of oxidation in the intestines, and it can be manifested as blood in vomiting and blood in stools (dark red blood in stools) when the bleeding is large and even hemorrhagic peripheral circulatory failure and anemia may occur. Upper gastrointestinal bleeding greater than 5 ml per day will result in a positive fecal occult blood test; if it is greater than 50 ml, it may be manifested as black stools. Common causes of upper gastrointestinal bleeding include peptic ulcer, acute erosive hemorrhagic gastritis, rupture of esophagogastric fundal varices, and upper gastrointestinal tumors. In addition, the lower gastrointestinal bleeding is mostly visible to the naked eye because the bleeding site is close to the anus, but there are some patients with lower gastrointestinal bleeding who will have black stools. You can improve the fecal occult blood test and colonoscopy to make it clear. Warm reminder: the symptoms of black stools, after excluding the influence of food and drugs, there are still symptoms of black stools, you need to consult a doctor in time to avoid adverse effects.