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.

How antacids work

Antacids work by counteracting (neutralising) the acid in your stomach that is used to aid digestion. This can reduce the symptoms of heartburn and relieve pain.

Some antacids also coat the surface of the oesophagus (gullet) with a protective barrier against stomach acid or produce a gel on the stomach’s surface which helps stop acid leaking into 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.

Who cannot take antacids?

Antacids are not suitable for everyone.

For example, many antacids are not recommended for children under the age of 12 and people with certain health conditions (such as kidney disease). Antacids can also interfere with other medications, so you may not be able to take them while you are being treated for another condition.

Antacids are generally considered safe to take during pregnancy, but you should discuss it with your GP or pharmacist beforehand.

Read more about who cannot take antacid medicines.

What are the possible side effects?

Like all medicines, antacids can have side effects. Common side effects include:

If you experience either constipation or diarrhoea after taking antacids, it may be possible to switch to an alternative medicine. Speak to your GP or pharmacist for advice.

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

Missed or extra doses

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

If you miss a dose of an antacid, it will usually not be necessary to alter your next dose. It is likely that you can carry on taking your normal dose. For specific advice about what to do, refer to the patient information leaflet that comes with your medicine.

Taking extra doses could cause several unpleasant side effects, such as nausea, vomiting, diarrhoea and constipation.

Contact your GP or pharmacist immediately if you think that you have taken more antacids than you should have. Alternatively, you can call NHS Direct on 0845 46 47 or NHS 111 for advice.


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).

Eat right for your digestion

How to eat and drink to ensure a good digestion, including foods to avoid and which ones to fill up on.

Page last reviewed: 12/12/2012

Next review due: 12/12/2014