The main causes of sudden black stools after a few days of stomach pain include consuming too many animal blood products or offal, taking bismuth supplements, but you also need to be alert to conditions such as gastrointestinal bleeding. 1. Consuming too much animal blood products or offal: Whether you are a patient with a stomachache or a healthy person, consuming too much pig liver, pig blood and other animal offal or animal blood products can lead to black feces. The reason is mainly because animal offal and blood contain more hemoglobin, which can be transformed into black ferrous ions after intake into the body, thus leading to black stool. 2. Taking bismuth: Helicobacter pylori infected people can have stomach pain, bloating and other discomforts, bismuth can treat Helicobacter pylori infection, its color is black, when the bismuth is not fully absorbed, it can be discharged with the stool, so that the stool is black. Bismuth can cause nausea, constipation and other adverse reactions, banned for pregnant women, bismuth does not usually cause stomach pain. 3. Gastrointestinal bleeding: gastric ulcer, duodenal ulcer and other symptoms of stomach pain, if not treated in time, may lead to gastric ulcer hemorrhage or duodenal hemorrhage, the blood through the gastrointestinal tract out of the body, black stools can be formed. Bleeding from ruptured esophageal varices in patients with cirrhosis can also lead to black stools, stomach pain and other symptoms. The above medications need to be taken as prescribed by your doctor. There are many reasons for stomach pain or black stool. If the symptoms of stomach pain or black stool do not subside or are accompanied by other symptoms, you should go to the hospital in time to get a clear picture of the cause and then give targeted treatment.