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Antacid medicines

Page last reviewed: 13/07/2011

Antacids are a type of medication that are available over the counter from pharmacies and are used to treat the symptoms of heartburn and acid indigestion.


Heartburn is burning chest pain or discomfort that occurs when stomach acid leaks out of the stomach and into the oesophagus (gullet). The acid irritates the surface of the oesophagus which causes the burning sensation in the chest. The medical term for this is gastro-oesophageal reflux disease (GORD).

How antacids work

Antacids can work in two ways. They can:

  • coat the surface of the oesophagus with a protective barrier against stomach acid
  • produce a gel on the stomach's surface which helps stop acid leaking up into the oesophagus, preventing the symptoms of heartburn

Antacids work by neutralising any acid that is in your stomach, reducing heartburn symptoms and relieving pain.

Antacids can also be combined with other medicines to help relieve the symptoms of heartburn. A number of different antacid medicines are available which all have different brand names.

Are antacids effective?

There is evidence to show that antacids are effective in providing short-term relief for heartburn.

However, long-term use is not recommended because there are more effective prescription medications that can be used to treat recurring heartburn, such as proton-pump inhibitors (PPIs). PPIs work by reducing the amount of acid that your stomach produces.

There is a lack of evidence showing that the long-term use of antacids is effective in relieving pain that is associated with heartburn.

Lifestyle changes, such as changes to your diet, can help to reduce the symptoms of heartburn. For more information and advice see heartburn - treatment.

Visit your GP if the symptoms of heartburn persist for more than a week or if they quickly return after the effects of the antacids has worn off.

Most antacids are not recommended for children under the age of 12. Read more about who can use antacids.

Page last reviewed: 13/07/2011

Antacid medicines are available in the form of both chewable tablets and liquids.

Examples of antacids include:

  • aluminium hydroxide
  • magnesium carbonate
  • magnesium hydroxide
  • magnesium trisilicate

As well as being used on their own, antacids can be combined with medicines such as simeticone and alignates.

Antacids and simeticone

Some antacids contain an added ingredient called simeticone. This combination helps relieve the symptom of flatulence (wind). 

Antacids and alignates

Antacid medicines can also contain another group of medicines, called alignates. Alignates form a protective layer on the surface of your stomach which prevents acid flowing into your oesophagus (gullet).

Sodium alginate is found in most medicines that are used to treat indigestion and gastro-oesophageal reflux disease (GORD).

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Page last reviewed: 13/07/2011

Use in children

Most antacid medicines are not recommended for children who are under the age of 12.

Antacids that contain calcium and are taken for long periods of time are not recommended for children because they can interfere with the rate that calcium is absorbed into the body and carried through the bloodstream. The right levels of calcium are vital for healthy bones and childhood development.

Prolonged use of antacids that contain calcium can also lead to the body's alkali levels becoming unbalanced and abnormally high, resulting in symptoms of muscle weakness and cramp.

There have also been a number of cases linking the prolonged use of antacids that contain magnesium and aluminium with rickets, a developmental disorder in infants that causes softening and weakening of the bones.

Always read the patient information leaflet that comes with a medicine or the packaging to ensure that it is suitable for children and to check the correct dosage.

Antacids that contain aluminium should not be used:

  • in children with kidney disease
  • in infants who are under the age of two
  • in babies  

Always seek the advice of your GP or pharmacist about giving antacids to children who are under 12 years old.

Use in pregnancy

Most types of antacids are generally considered to be safe to take during pregnancy.

However, if you are pregnant or breastfeeding, seek advice from your GP or pharmacist before starting to take antacids.

Use with other medicines

Antacids may interfere with your body's ability to absorb other types of medication, particularly if you take them together, at the same time.

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Page last reviewed: 13/07/2011

All medicines have potential side effects. Before starting to take antacid medicines, you may want to discuss any potential side effects with your GP or pharmacist.

A study investigating the use of antacids found that around 1 in 10 people who took them experienced side effects such as:

  • diarrhoea
  • feeling sick
  • being sick
  • blood in their stools
  • flatulence (wind)
  • constipation

Antacids that contain aluminium can cause constipation in some people, while those with magnesium can cause diarrhoea.

If you experience either constipation or diarrhoea after taking antacids, a medicine that contains both ingredients may be more suitable and help prevent these unwanted side effects. Speak to your GP or pharmacist for advice.

Any side effects that you experience while taking antacids should pass once you stop taking the medication. However, visit your GP if you continue to experience side effects after you stop taking the medication.

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Page last reviewed: 13/07/2011

Taking antacids can interfere with your body's ability to absorb other medications that you are taking at the same time.

Therefore, you may be advised to stop taking other medication for a certain amount of time while you are taking antacids.

It's important never to stop taking a medication that has been prescribed for you without first consulting your GP or another suitably qualified healthcare professional.

Other health conditions

Antacids that contain high levels of magnesium and aluminium may be harmful for people with a history of kidney disease. Also, some antacids contain high levels of salt and may be harmful for people with high blood pressure. Ask your GP or pharmacist for advice about which antacids are suitable for you if you have either of these conditions.

Before taking antacids regularly, also ask your GP or pharmacist for advice if you:

  • are taking calcium supplements - for example, for a condition such as osteoporosis, which causes weak and fragile bones
  • have had kidney stones
  • are taking medication for another health condition on a regular basis

Page last reviewed: 13/07/2011

Take antacid medicines as directed on the patient information leaflet that comes with the medicine (or on the packet), or as advised by your GP or pharmacist.

Missed doses

If you miss a dose of an antacid, it will usually not be necessary to double the dose the next time that you take the medication. It is likely that you can carry on taking your normal dose, regardless of the dose that you missed.

For specific advice about what to do, refer to the patient information leaflet that comes with your medicine.

Extra doses

It's important to stick to the recommended doses of antacids because extra doses could cause several unpleasant side effects, such as:

  • feeling sick
  • being sick
  • upset stomach
  • diarrhoea 
  • constipation

Contact your GP or pharmacist immediately if you think that you have taken more antacids than you should have.

Content provided by NHS Choices www.nhs.uk and adapted for Ireland by the Health A-Z.

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