Histamine-2 antagonists (also called H2 blockers) are used to relieve heartburn and treat conditions like gastroesophageal reflux disease (GERD) and peptic ulcers. They work by blocking histamine-2 receptors in your stomach, which reduces the amount of acid your stomach produces. Histamine-2 antagonists come in different forms, including oral pills and solutions. Examples include famotidine (Pepcid AC, Zantac 360) and cimetidine (Tagamet HB). You can choose the form that best fits your needs.