Metformin, also known as cimetidine, has another trade name of Tegretol. Its main action is to inhibit gastric acid secretion and it is the first generation of H2 receptor blocker, followed by the second generation of ranitidine, and the third generation of famotidine, which has a stronger acid-suppressing effect, and because it blocks H2 receptors, it also has an anti-allergic effect. However, it has serious side effects, such as gynecomastia, and also able to pass through breast milk and placenta, so pregnant women and children under 16 years old are avoided, and extravertebral reactions can occur with prolonged use, and adverse reactions should be closely observed during use, and these side effects limit its use in clinical practice. Currently there are stronger acid inhibitors, such as proton pump inhibitors, which are rarely used in clinical practice as a treatment for gastric diseases.