An antacid is a substance which neutralizes stomach acidity.
Antacids are available over the counter and are taken by mouth to quickly relieve occasional heartburn, the major symptom of gastroesophageal reflux disease, or acid indigestion. Treatment with antacids alone is symptomatic and only justified for minor symptoms.
Antacids are distinct from acid-reducing drugs like H2-receptor antagonists or proton pump inhibitors and they do not kill the bacteria, Helicobacter pylori, which causes most ulcers.
Versions with magnesium may cause diarrhea, and brands with calcium or aluminium may cause constipation and rarely, long-term use may cause kidney stones. Long term use of versions with aluminum may increase the risk for getting osteoporosis.
Mechanism of action
Antacids contain alkaline ions that directly neutralize stomach gastric acid.
Some well-known antacid brands
Antacids are generally a chemical salt of an alkaline ion and a counterion, as shown in the table below. The alkaline ion is generally bicarbonate but may also be hydroxide.