The most common causes of upper gastrointestinal bleeding. The first is hemorrhage due to peptic ulcers. The second is bleeding from ruptured esophageal and gastric varices. The third is acute erosive hemorrhagic gastritis. The fourth is bleeding caused by gastric cancer. The fifth is bleeding caused by Mallory-Weiss syndrome. After the occurrence of gastrointestinal bleeding, it is necessary to seek medical attention promptly, undergo treatments like hemostasis and blood transfusion in the hospital, and actively manage the symptoms. If necessary, a gastroscopy can be performed for endoscopic hemostasis. If not treated actively, emaciated individuals' lives may be at risk, so caution is necessary.