The causes of black stools may include dietary or medication effects and gastrointestinal bleeding, the former of which is not serious, while the latter is usually more serious. Some foods and medications can cause black stool color, especially foods containing a lot of hemoglobin and iron such as duck blood, and common medications include rifampicin and ferrous sulfate. This is not a serious condition and can return to normal after stopping eating or stopping medication for a period of time. Iron in hemoglobin in the blood, through the action of bacteria in the intestine to form iron sulfide, which is a black substance, will lead to dark and shiny stools, called tarry stools. This is a serious condition. For the specific cause and severity of the disease, it is recommended that the patient consult a doctor in a timely manner, complete gastroscopy and other relevant examinations to clarify, and actively cooperate with the doctor for treatment.