H2 receptor antagonists are a class of medications that block the action of histamine on H2 receptors in the stomach lining. By doing so, they reduce the production of stomach acid, which can help treat conditions like gastroesophageal reflux disease (GERD) and peptic ulcers. These medications are often available over-the-counter and include drugs like ranitidine and famotidine. They are generally well-tolerated, but potential side effects can include headaches, dizziness, and gastrointestinal issues. Always consult a healthcare professional before starting any new medication.