H2 antagonists inhibit gastric acid secretion. H2 antagonists, also known as H2 receptor blocking drugs, can competitively block the H2 receptor on the mural cells and inhibit the secretion of basal and nocturnal gastric acid, mainly used in the treatment of gastric and duodenal ulcers, can reduce the pain caused by ulcers and promote the healing of gastric and duodenal ulcers. H2 receptor blocking drugs include cimetidine, ranitidine, famotidine, nizatidine, rosatidine and so on. The incidence of adverse reactions to H2 receptor blocking drugs is low, with mild diarrhea, constipation, dizziness, and malaise common. The drugs are mainly metabolized by the kidneys, and long-term use by the elderly and those with poor hepatic and renal function may lead to drug involvement, with neurological symptoms such as confusion, slurred speech and even coma. H2 receptor blocking drugs should be used properly under the guidance of gastroenterologist.