Which drug is commonly used as an H2 receptor antagonist?

Famotidine is commonly used as an H2 receptor antagonist, which works by inhibiting the action of histamine at the H2 receptors in the stomach lining. This leads to a decrease in gastric acid secretion, making it effective in treating conditions such as peptic ulcers, gastritis, and gastroesophageal reflux disease (GERD). H2 receptor antagonists like famotidine reduce the volume and concentration of stomach acid, providing relief from symptoms associated with excess acid production.

The other drugs listed serve different purposes. Esomeprazole is a proton pump inhibitor, which works differently by blocking the final step in gastric acid production, and is mainly used for similar indications as famotidine but through a different mechanism. Dextromethorphan is primarily an antitussive, used to suppress cough, and does not have an impact on gastric acid secretion. Guaifenesin is an expectorant, aimed at relieving chest congestion by thinning mucus, and does not interact with H2 receptors or influence gastric acid production.