Black stool may be caused by dietary or medication factors, or it may be caused by gastrointestinal bleeding and other disease factors. 1. Dietary factors: After eating iron rich foods such as chicken blood, duck blood, pig blood, etc., iron can produce iron sulfide under the action of intestinal bacteria leading to black stools. 2. Drugs: Taking iron and bismuth agents such as ferrous succinate and bismuth potassium citrate can also cause black stools. 3. Disease factors: gastric ulcer, esophageal varices rupture bleeding, gastrointestinal tumors and other diseases or taking aspirin and other drugs can cause gastrointestinal bleeding, resulting in the discharge of black stool. If you have black stools, it is recommended to go to the hospital and ask the doctor to determine the cause of the black stools by combining with your own condition after eliminating the factors of diet and taking iron and other medications.