H2 blockers, or histamine-2 receptor antagonists, are a class of medications that reduce the amount of acid produced by the stomach. They work by blocking the action of histamine on the H2 receptors in the stomach lining, which helps alleviate conditions like gastroesophageal reflux disease (GERD) and peptic ulcers. Common H2 blockers include ranitidine, famotidine, and cimetidine. These medications are available both over-the-counter and by prescription, and they are generally used for short-term relief of heartburn and acid-related issues. While effective, they may have side effects and should be used under the guidance of a healthcare professional.