Taking iron supplements black stools is mainly considered to be the reaction of the drug in the intestinal tract to produce black iron sulfide, but also need to rule out food, gastrointestinal bleeding causes. The main ingredient of iron supplements (such as ferrous sulfate tablets) includes ferrous sulfate, which can react with hydrogen sulfide in the intestines to produce iron sulfide, which is black in color and mixes with feces to form black stools, which is a normal phenomenon. Black stools may also be associated with eating iron-rich foods, such as blood products, or taking other medications, such as bismuth potassium citrate and other bismuth agents, may also be bleeding in the digestive tract. Therefore, black stools exclude the cause of food, drugs, but also need to guard against gastrointestinal bleeding, if necessary, should be perfect blood, stool routine, gastroenteroscopy and other related examinations to clarify the cause of the disease.