Histamine H2 antagonists are a class of medications that block the action of histamine on H2 receptors in the stomach lining. This action reduces the production of stomach acid, helping to treat conditions like gastroesophageal reflux disease (GERD) and peptic ulcers. Common examples of H2 antagonists include ranitidine and famotidine. These medications are typically available over-the-counter and are used to relieve symptoms such as heartburn and indigestion. They are generally considered safe for short-term use, but long-term use should be monitored by a healthcare professional.