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A bottle of antacid tablets

An antacid is any substance, generally a base, which counteracts stomach acidity. In other words, antacids are stomach acid neutralizers.

Action mechanism

Antacids sucks the pain when you have just had a peptic ulcer. They perform a neutralization reaction, i.e. they buffer gastric acid, raising the pH to reduce acidity in the stomach. When gastric hydrochloric acid reaches the nerves in the gasitrointestinal mucosa, they signal pain to the central nervous system. This happens when these nerves are exposed, like in ulcers. The gastric acid may also reach ulcers in the esophagus or the duodenum.

Other mechanisms may contribute, such as the effect of aluminum ions inhibiting smooth muscle cell contraction and delaying gastric emptying.


Antacids are taken by mouth to relieve heartburn, the major symptom of gastroesophageal reflux disease, or acid indigestion. Treatment with antacids alone is symptomatic and only justified for minor symptoms. Peptic ulcers may require H2-receptor antagonists or proton pump inhibitors.

The usefulness of many combinations of antacids is not clear, although the combination of magnesium and aluminum salts may prevent alteration of bowel habits.

Side effects


Altered pH or complex formation may alter the bioavailability of other drugs, such as tetracycline. Urinary excretion of certain drugs may also be affected.

Problems with reduced stomach acidity

Reduced stomach acidity may result in an impaired ability to digest and absorb certain nutrients, such as iron and the B vitamins. Since the low pH of the stomach normally kills ingested bacteria, antacids increase the vulnerability to infection.

Drug names

Examples of antacids (brand names may vary in different countries).

de:Antazidum hr:Antacidi nl:Antacidum sk:Antacidum sl:Antacid sr:Антацид fi:Antasidi sv:Antacida th:ยาลดกรด