Antacids are a type of medication that can control the acid levels in your stomach.

They're available over the counter from pharmacies and are often used to treat the symptoms of heartburn and indigestion.

How antacids work

Antacids counteract (neutralise) the acid in your stomach that's used to aid digestion. This helps reduce the symptoms of heartburn and relieves 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 and causing acid reflux.

Different types of antacids

Antacids are available in liquid form or as chewable tablets. They're sold under various brand names but contain common ingredients, including:

  • aluminium hydroxide
  • magnesium carbonate
  • magnesium trisilicate

Extra ingredients are sometimes added to help treat other problems, such as simeticone to relieve flatulence (wind), and alginates to prevent acid flowing into your oesophagus.

Who can't take antacids?

Antacids aren't suitable for everyone. For example, many antacids aren't 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're 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 can't take antacid medicines.

Possible side effects of antacids

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

If you have diarrhoea or constipation 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. Visit your GP if they continue.

Missed or extra doses

When taking antacid medicines, follow the instructions on the patient information leaflet that comes with the medicine or the advice of your GP or pharmacist.

If you miss a dose, it won't usually be necessary to alter your next dose. It's likely that you can carry on taking your normal dose. However, 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've taken more antacids than you should have. Alternatively, you can call NHS 111 for advice.

Page last reviewed: 19/12/2014

Next review due: 19/12/2016