Left-sided stomach pain is usually caused by chronic gastritis, gastric ulcer and other diseases. Chronic gastritis is caused by edema and congestion of the gastric mucosa, while gastric ulcer is caused by damage to the protective barrier of the gastric mucosa and the appearance of ulcerated surfaces. These two diseases are the most common in the stomach and can occur in any part of the stomach. When the patient’s lesion is located on the left side of the stomach body and fundus, stomach acid will come into direct contact with the left side of the stomach body and fundus when the body is lying on the left side. The stomach acid itself is irritating because the protective barrier of the gastric mucosa has been damaged, so it is not possible to isolate the stomach acid from the stomach wall, and a painful sensation in the stomach occurs. People who often experience stomach pain should be treated as early as possible with medications, mainly drugs that inhibit gastric acid secretion and promote mucosal repair, such as omeprazole, lansoprazole, and colloidal bismuth pectin.