Antacids are a type of medication that can control the acid levels in your stomach. They are available over the counter from pharmacies and are commonly used to treat the symptoms of heartburn and indigestion.

What are antacids?

Antacids are agents that neutralize the gastric acid and raise the gastric pH, so are used to treat dyspepsia and are used as symptomatic relief of peptic ulcer. Antacids in common use salts of magnesium, aluminium and calcium. Some mixtures contain sodium and should be used with caution in patients who should avoid excess sodium intake. Alginates are sometimes combined with antacids for use in gastroesophageal reflux disease. Alginates float on top of the gastric contents and act as a barrier between the acidic contents of the stomach and the lower oesophageal sphincter, preventing erosion of the lower esophagus and therefore not creating the pain experienced in gastroesophageal reflux disease.

What conditions are antacids used to treat?

Antacids may be used:

  • To reduce the symptoms of acid reflux which may cause heartburn or oesophagitis (inflammation of the gullet). These conditions are sometimes called gastro-oesophageal reflux disease (GORD).
  • To relieve some of the symptoms caused by ulcers in the stomach and duodenum (part of the gut).
  • In other conditions where it is helpful to neutralise stomach acid. For example, for occasional bouts of dyspepsia (indigestion).
  • Before the discovery of other more modern medicines, antacids were commonly used for the above conditions. They were also used to help heal ulcers in the stomach and duodenum.
  • Modern medicines called proton pump inhibitors and H2-receptor antagonists (commonly called H2 blockers) are now more widely used for these conditions, as they are much more effective than antacids. Unlike antacids, which simply neutralise the acid for a short period, these modern medicines work by reducing the amount of acid made by the stomach.
  • However, antacids still have a place. They are most commonly used to provide quick relief of symptoms caused by stomach acid. In particular, in people who get intermittent bouts of mild dyspepsia (indigestion) or heartburn.

How do antacids work?

  • Your stomach normally produces acid to help with the digestion of food and to kill bacteria. This acid is corrosive so your body produces a natural mucus barrier which protects the lining of the stomach from being eroded.
  • In some people this barrier may have broken down allowing the acid to damage the stomach, causing an ulcer. In others there may be a problem with the muscular band at the top of the stomach (the sphincter) that keeps the stomach tightly closed. This may allow the acid to escape and irritate the oesophagus (gullet). This is called acid reflux, which can cause heartburn and/or oesophagitis.
  • Antacids work by neutralising (counteracting) the acid in your stomach. They do this because the chemicals in antacids are bases (alkalis) which are the opposite of acids. A reaction between an acid and base is called neutralisation. This neutralisation makes the stomach contents less corrosive. This can help to relieve the pain associated with ulcers and the burning sensation in acid reflux.
  • When antacids work on stomach acid, they can produce gas which may cause flatulence (wind). Simeticone helps to stop this foaming effect and may sometimes be included within antacid medications.
  • Many of the common antacids also include alginates. Most alginates work by forming a gel which floats on top of the stomach contents. The gel acts as a protective barrier, preventing stomach acid from irritating the oesophagus.

Different types of antacids

Antacids are available in the form of chewable tablets or liquid. They are sold under various brand names, but they contain common ingredients, including:

  • aluminium hydroxide
  • magnesium carbonate
  • magnesium trisilicate

Sometimes extra ingredients are added to help treat other problems, such as simeticone to relieve flatulence and alginates to prevent acid flowing into your oesophagus.

What are the side-effects?

  • Most people who take an antacid do not have any side-effects. However, side-effects occur in a small number of users. The most common are diarrhoea, constipation and belching.
  • Magnesium-containing antacids tend to be laxative whereas aluminium-containing antacids tend to be constipating. Antacids containing both magnesium and aluminium may balance out these effects and so minimise any possible side-effects of diarrhoea or constipation.
  • For a full list of all the side-effects and possible interactions associated with your medicine, consult the leaflet that comes with your medication.
  • If you are taking antacids, you should avoid taking them at the same time as you take other medication. This is because antacids can affect how well other medication is absorbed.


Health Reference: Heartburn, Indigestion