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Antacids neutralise the acid made by your stomach. They are commonly used for indigestion and acid reflux which causes heartburn. Most people who take antacids do not develop any side-effects.

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What are antacids?

Antacids are a group (class) of medicines which help to neutralise the acid content of your stomach.

Some antacids are combined with another medicine called simeticone which helps to reduce wind (flatulence).

Another group of medicines called alginates are found in some brands of antacid medication. Alginates are added to help protect the lining of the gullet (oesophagus) from stomach acid.

Alginates include sodium alginate and alginic acid. They are present in antacid medications.

Types of antacids

Antacids include:

These come in various brand names and are available as tablets and liquids.

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What conditions are antacids used to treat?

Antacids may be used:

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.

Medicines called proton pump inhibitors (PPIs) and H2-receptor antagonists (commonly called H2 blockers) are now more widely used for these conditions. 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.

Note: some studies have questioned whether long-term use of PPIs may be linked to stomach cancer. More studies are needed. Therefore, current advice is that PPIs should be taken at the lowest dose, for the shortest length of time possible.

Some people may be able to take them occasionally rather than on a daily basis. However, if you find that other medicines don't help and you have persistent symptoms, the advice is to carry on taking PPI medication for as long as necessary.

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 have occasional bouts of mild dyspepsia or heartburn.

How do antacids work?

Upper gastrointestinal tract and acid

Upper GI Tract and acid

Your stomach normally produces acid to help with the digestion of food and to kill germs (bacteria). This acid is corrosive so your body produces a natural mucous barrier which protects the lining of the stomach from being worn away (eroded).

In some people this barrier may have broken down and this allows 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, allowing the acid to escape and irritate the gullet (oesophagus). This is called acid reflux, which can cause heartburn and/or inflammation of the gullet (oesophagitis).

Antacids work by counteracting (neutralising) 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 wind (flatulence). 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.

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Antacid 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:

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.

Can I buy antacids or do I need a prescription?

You can buy most brands of antacids at pharmacies, or you may obtain them on prescription.

When is the best time to take antacids?

Antacids are often taken to relieve symptoms or when symptoms are expected. Your doctor or pharmacist will advise you of the dose needed and how often you should take it. Read the leaflet that comes with your particular brand for further information.

How quickly do antacids work?

Generally antacids provide quick relief for problems such as heartburn caused by reflux. However, the relief of symptoms may only be short-lived.

How long is treatment needed for?

Your doctor may prescribe an antacid to have on standby so that you only take it to relieve your symptoms when they occur, rather than every day. Read the leaflet that comes with your particular brand for further information.

Who can and cannot take antacids?

A full list of people who should not take antacids is included with the information leaflet that comes in the medicine packet. If you are prescribed or buy an antacid, read this to be sure you are safe to take it.

Other considerations

You should talk to your doctor if your symptoms worsen, or if you experience any of the following problems which can indicate a serious gut disorder:

  • Bringing up (vomiting) blood. This may be obviously fresh blood but altered blood in vomit can look like dark brown or black ground coffee. This is called coffee-ground vomit.

  • Blood in your stools (faeces). This may be obvious blood, or it may make your stools black.

  • Unintentional weight loss.

  • Difficulty swallowing, including food getting stuck in the gullet (oesophagus).

  • Persistent tummy (abdominal) pain.

  • Persistent vomiting.

Further reading and references

Article history

The information on this page is written and peer reviewed by qualified clinicians.

  • Next review due: 8 Aug 2028
  • 10 Aug 2023 | Latest version

    Last updated by

    Dr Surangi Mendis

    Peer reviewed by

    Dr Doug McKechnie, MRCGP
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