Aluminum hydroxide is a typical and commonly used antacid. It has the functions of acid resistance, sorption, local hemostasis, and protection of ulcer surface. Aluminum hydroxide acts as a chemical reaction to neutralizing or buffering the existing gastric acid in the stomach, but has no direct effect on the secretion of gastric acid, and its acid resistance is slow and persistent. Neutralization and buffering of aluminum hydroxide can lead to an increase in the pH content of gastric contents, thereby relieving the symptoms of gastric acid excess. However, it should be pointed out that the ability of acid is lower than that of magnesium and calcium carbonate, higher than that of aluminum carbonate and sodium dihydroxycarbonate. Aluminum hydroxide can react with gastric acid to produce aluminum chloride, which can partially stop bleeding, but it may also cause constipation. Aluminum hydroxide can react with gastric acid to produce aluminum chloride, which can partially stop bleeding, but it may also cause constipation. Aluminum hydroxide is also mixed with gastric juice to form gel, covering the surface of ulcer to form a protective film, which has mechanical protection function. In addition, as aluminum ions are produced in the intestines with phosphate, the insoluble aluminum phosphate is discharged from the feces, so the uremic patients take large doses of aluminum hydroxide to reduce the absorption of phosphate in the intestinal tract, thereby reducing acidemia (but at the same time, attention should be paid to the above side effects).