A patient with gastroesophageal reflux disease (GERD) is prescribed the histamine antagonist, cimetidine. How does cimetidine pharmacologically reduce the amount of stomach acid?

By neutralizing existing stomach acid through its alkaline properties.

By stimulating the production of bicarbonate to buffer the stomach acid

By inhibiting the proton pump enzyme, preventing hydrogen ion exchange in parietal cells

By selectively blocking H2 receptors in the stomach which suppresses gastric acid secretion.