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How do H2-blocking drugs reduce the effects of histamine in the stomach?

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H2-blocking drugs, or H2 receptor antagonists, reduce the effects of histamine in the stomach by selectively blocking histamine from binding to its H2 receptors on the surface of parietal cells.12

Normally, histamine acts as a chemical messenger that stimulates these parietal cells to produce hydrochloric acid. By occupying these receptor sites, H2-blocking agents—such as cimetidine and ranitidine—prevent histamine from triggering this secretory process. Furthermore, these drugs are effective at blocking other stimulants of acid secretion, including the hormone gastrin and food. By inhibiting this acid production, these medications help treat conditions involving gastric hypersecretion, such as peptic ulcers and gastroesophageal reflux.1234