Final answer:
Cimetidine works by blocking histamine H₂ receptors in the stomach to reduce acid production, treating disorders like ulcers and GERD.
Step-by-step explanation:
The mechanism of action of Cimetidine, an H₂ blocker, involves the inhibition of histamine action at the histamine H₂ receptors of the gastric parietal cells. This inhibition results in a decrease in the production of gastric acid, which is useful in the treatment of conditions associated with excessive stomach acid production, such as ulcers, gastroesophageal reflux disease (GERD), and Zollinger-Ellison syndrome. Cimetidine is different from other classes such as proton pump inhibitors, as it does not inhibit the gastric acid pump but rather blocks the action of histamine that stimulates acid secretion.