Black stools are generally caused by upper gastrointestinal tract bleeding, which can stem from several reasons:

The first one is peptic ulcer, including stomach ulcers and duodenal ulcers;

The second is bleeding caused by varices rupturing in the esophagus or stomach due to liver cirrhosis;

The third is acute gastric mucosal injury, for example, gastric bleeding caused by orally taken non-steroidal anti-inflammatory drugs;

The fourth is gastric hemorrhage caused by gastric cancer.

No matter what causes the upper gastrointestinal bleeding, one should promptly visit a hospital, undergo a gastroscopy to determine the cause, and receive timely rescue and treatment. Moreover, during the treatment period, one cannot eat while experiencing gastric bleeding, and must fast until the bleeding stops, after which a liquid diet can be introduced, followed by a transition to a semi-liquid diet.