antacid

An antacid is like a chemical sponge for stomach acid: you swallow a base that meets the acid already sitting in your stomach and neutralizes it on the spot, taking the burn out of heartburn within minutes.

Common antacids are simple inorganic bases or salts — aluminium hydroxide, magnesium hydroxide, calcium carbonate, and sodium bicarbonate. They react with hydrochloric acid to raise the gastric pH and reduce the activity of pepsin, the acid-dependent protein-digesting enzyme. Because they act on acid that is already present rather than on the cells that make it, they work fast but only for a few hours, until the stomach refills with acid.

Antacids relieve symptoms but do not switch off acid production, so for healing ulcers or treating significant reflux they are weaker than acid-suppressing drugs. Side effects track the metal: aluminium tends to cause constipation, magnesium tends to cause diarrhoea (so the two are often combined), and calcium or sodium loads matter in kidney or heart disease. They can also bind other drugs in the gut and reduce their absorption, so dosing is usually separated in time.