H2 antagonists are a class of medications that reduce stomach acid production. They work by blocking the action of histamine on H2 receptors in the stomach lining, which decreases the secretion of gastric acid. This helps treat conditions like gastroesophageal reflux disease (GERD) and peptic ulcers. Common examples of H2 antagonists include ranitidine, famotidine, and cimetidine. These medications are often available over-the-counter and are used to relieve symptoms such as heartburn and indigestion. While generally safe, they can have side effects and may interact with other drugs, so it's important to consult a healthcare provider before use.