What causes the stool to be black

Stool blackening may be due to the recent consumption of pig liver, duck liver, pig blood, duck blood and other iron-rich foods, combined with sulfide in the intestinal tract to form iron sulfide excreted out of the body, or taking colloidal bismuth pectin, ferrous succinate, activated carbon and other drugs to cause physiological melena; it may also be due to the existence of gastric ulcer, duodenal ulcer, chronic gastritis, esophageal and gastric varices and other diseases, leading to upper gastrointestinal bleeding, and causing melena. Long-term melena patients need to go to the hospital for systematic examination, clear cause, timely symptomatic treatment.