Black stools can be produced by food and drugs. Food is mainly some special green vegetables, or animal blood products and offal. Patients who eat these iron-rich foods will produce black stools, such as eating pig blood, sheep blood, chicken, duck and goose blood, and eating a lot of beef and pig liver. The iron in the blood of these animals can form black iron sulfide in the human intestine and make the stool black in color. Of course there are some foods, such as eating some prune jam and mulberry jam, may also cause the color of the stool to darken. And then there are some drugs to eat can also appear black stool, such as oral activated charcoal end and blood iron supplements, as well as some bismuth agents commonly used in gastroenterology, and even some Chinese medicine may lead to black stools.