How do over-the-counter antacids primarily function?

Over-the-counter antacids primarily function by neutralizing stomach acid with carbonate or hydroxide ions. These substances work to raise the pH level of the gastric contents, thus providing relief from symptoms associated with excess stomach acidity, such as heartburn and indigestion. When antacids come into contact with hydrochloric acid in the stomach, they undergo a chemical reaction that results in the formation of water and other neutral compounds, effectively reducing acidity.

Other mechanisms described in the options pertain to different classes of medications. The role of blocking histamine receptors, for instance, is characteristic of H2 receptor antagonists, which are designed to reduce gastric acid secretion rather than neutralizing existing acid. Inhibiting proton pumps is the primary action of proton pump inhibitors, which differ significantly from the mechanism of antacids. Promoting gastric motility is associated with prokinetic agents, not antacids. Thus, the focus on chemical neutralization is what fundamentally distinguishes antacids in their therapeutic approach to managing conditions related to gastric acidity.