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Antacids are medicines that counteract (neutralise) the acid in your stomach. They are used to relieve indigestion and heartburn.

Many different types of antacid are available.

They come as a liquid or chewable tablets. You can buy them from pharmacies and shops without a prescription.

Some are sold under a brand name and others are named after their main ingredient.

Common brand names include Rennie, Gaviscon, Maalox, Bisodol, and Milk of Magnesia.

Ingredients to look for include:

  • aluminium hydroxide
  • magnesium carbonate
  • magnesium trisilicate
  • magnesium hydroxide
  • calcium carbonate
  • sodium bicarbonate

Some antacids also contain other medicines, such as:

  • alginate - this coats your gullet with a protective layer
  • simeticone - this helps reduce bloating and trapped wind (farting)

Uses of antacids

Antacids may help if you have:

  • indigestion
  • heartburn or acid reflux – also known as gastro-oesophageal reflux disease (GORD)

Your GP may decide to use antacids to help treat stomach ulcers and gastritis (inflammation of the stomach lining).

They can relieve your symptoms for a few hours. But they do not treat the underlying cause.

Long-term use of antacids is not recommended. Taking antacids for a long time may mask the signs of more serious disease.

Talk to your GP if you are taking antacids often.

Severe allergic reaction

A severe allergic reaction (anaphylaxis) to antacids is rare. But you will need to go to an emergency department (ED) if you have symptoms of a severe allergic reaction.

Emergency action required: Go to an ED or phone a GP immediately if you:

  • get a skin rash
  • develop swelling
  • have shortness of breath

Stop taking the antacids you are on.

Check if you can take antacids

Antacids are safe for most people to take, but they are not suitable for everyone. Some antacids are not recommended for children.

Talk to a pharmacist or your GP for advice first if you:

  • are taking other medicines
  • are looking for a medicine for a child under 12 years of age
  • have liver disease, kidney disease or heart failure
  • need to control how much salt is in your diet
  • have high levels of calcium in your blood
  • have low levels of phosphate in your blood

Pregnant or breastfeeding

Most antacids are safe to take if you are pregnant or breastfeeding. But talk to a pharmacist or your GP for advice before taking them.

How and when to take antacids

Check the instructions on the packet or leaflet to see how much antacid to take and how often. This depends on the exact medicine you're taking.

Use antacids when you have symptoms or think you will get them soon. For most people, the best time to take them is with or soon after meals, and before going to bed.

Doses for children may be lower than for adults.

Talk to your GP or pharmacist if you take more than the recommended dose and start to feel unwell.

Eating and drinking

It's best to take antacids with food or soon after eating. This is when you're most likely to get indigestion or heartburn.

The effect of the medicine may also last longer if you take it with food.

You can drink alcohol while taking antacids. But alcohol can irritate your stomach and make your symptoms worse.

Side effects of antacids

Antacids do not have many side effects. But you should only take them from time to time and at the recommended dose.

Check the instructions on the packet or leaflet to see how much antacid to take and how to use this medicine.

Sometimes they can cause:

  • diarrhoea or constipation
  • farting (wind)
  • stomach cramps
  • feeling sick or vomiting

Any side effects should stop when you stop taking the medicine.

Talk to a pharmacist or a GP if side effects do not improve or are troublesome. You may need to switch to another medicine.

Read the patient information leaflet that comes with your medicine for a full list of side effects.

Non-urgent advice: Find your patient information leaflet

Your patient information leaflet is the leaflet that comes with your medicine. You can find a digital version of the leaflet online.

Report side effects

You can report any suspected side effects to the the Health Products Regulatory Authority (HPRA): report an issue -

Taking antacids with other medicines

Antacids can affect how well other medicines work. Sometimes, they can stop other medicines working properly.

Talk to a pharmacist or GP about taking antacids if you are taking other medicines or supplements.

Do not take other medicines within 2 to 4 hours of taking an antacid.

Fact check

This content was fact checked by a pharmacist, a GP, the National Medication Safety Programme (Safermeds) and the Health Products Regulatory Authority (HPRA).

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This project has received funding from the Government of Ireland’s Sláintecare Integration Fund 2019 under Grant Agreement Number 123.

Page last reviewed: 24 September 2021
Next review due: 24 September 2024