Taking iron supplements black stools is considered to be related to the role of drugs, but we can not rule out the possibility of gastrointestinal bleeding. 1. The effect of the drug, iron is a drug containing iron, when the iron into the body may be oxidized to form iron oxide, so it will produce black stool symptoms, usually a normal reaction. Not only can this symptom occur after taking medication, but also after consuming food containing coloring. 2. Gastrointestinal bleeding, if the process of taking drugs have gastrointestinal bleeding, such as gastritis, gastric ulcer, duodenal ulcer and other diseases may damage the gastric mucosa, gastrointestinal bleeding, may also have black stool symptoms. If this symptom still occurs after stopping the drug, it is recommended to actively seek medical examination and treatment.