A raft-forming heartburn and reflux remedy
Alginic acid (alginates)
An over-the-counter remedy that forms a protective layer on top of stomach contents to stop heartburn and acid reflux.
What is Alginic acid (alginates)?
Alginic acid, usually called an alginate, is a popular over-the-counter remedy for heartburn and acid reflux, found in products such as Gaviscon, Acidex and Peptac. When it reaches the stomach it forms a foamy, gel-like 'raft' that floats on top of the stomach contents, acting as a barrier so that acid is less likely to splash back up into the gullet. It is usually taken after meals and at bedtime, when reflux is most likely. Many alginate products also contain antacids, which neutralise acid as well, giving quick relief. It is widely used in pregnancy and is generally very safe, but persistent symptoms should be checked by a pharmacist or GP.
Education and reference only. This is a plain-language guide to Alginic acid (alginates) — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Alginic acid, more often called an alginate, is a substance derived from seaweed that is widely used in over-the-counter remedies for heartburn and acid reflux. Products such as Gaviscon, Acidex and Peptac usually combine an alginate with antacid ingredients, so they both neutralise acid and form a protective barrier. It is one of the most common pharmacy purchases for indigestion-type symptoms and is available without a prescription as a liquid or chewable tablet. It works physically in the stomach rather than being absorbed into the body, which is part of why it is so well tolerated.
How it works
When an alginate meets the acid in the stomach, it reacts to form a light, foamy gel that floats to the top of the stomach contents, rather like a raft on water. This raft sits over the area where reflux happens, so when stomach contents do move upwards, it is the gentle raft that rises into the gullet instead of harsh acid, easing the burning feeling. Because many products also contain an antacid, the acid itself is partly neutralised at the same time. The effect is local and physical, which is why alginates start to help quite quickly and are gentle on the rest of the body.
Company & origin
Originated / developed by: Various (widely available).
A pharmacy-shelf remedy used across the UK to ease heartburn and acid reflux, often combined with antacids in well-known products such as Gaviscon.
What it treats
Conditions Alginic acid (alginates) is used for
Practical use
How to take Alginic acid (alginates)
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Take it after meals and at bedtime, when reflux and heartburn are most likely.
- Shake the liquid well, or chew the tablets thoroughly, before swallowing.
- Leave a gap of a couple of hours between alginates and other medicines, as it can affect how they are absorbed.
- Use it for short-term relief, and see a pharmacist or GP if symptoms keep coming back or last more than a couple of weeks.
- Check the label or ask the pharmacist if you need a low-salt or sugar-free option.
Weighing it up
Advantages & disadvantages of Alginic acid (alginates)
Advantages
- Eases heartburn and acid reflux quickly by forming a protective barrier on the stomach contents.
- Gentle and very well tolerated, as it works in the stomach rather than being absorbed.
- A commonly recommended and well-trusted option in pregnancy and for night-time symptoms.
Disadvantages
- Gives short-term relief rather than treating the underlying cause of reflux.
- Some products contain salt or sugar, which can matter for certain people.
- Needs to be timed after meals and at bedtime to work at its best.
Practical use
Good to know
Alginates are best taken after meals and at bedtime, because this is when reflux is most likely and when the raft can do the most good; taking it on an empty stomach gives less benefit. Many people find it especially helpful for night-time heartburn and during pregnancy, when it is a commonly recommended option. Because it works in the stomach rather than being absorbed, it is gentle and suitable for most people, but some products contain salt (sodium) or sugar, which can matter for people watching their salt or blood sugar, so it is worth checking the label or asking the pharmacist. It is fine for short-term relief, but heartburn that keeps coming back, lasts more than a couple of weeks, or comes with difficulty swallowing, weight loss or being sick should be checked by a pharmacist or GP rather than treated indefinitely at home.
Who should not take it / use with caution
- People who have had an allergic reaction to an alginate product or its ingredients should not use it.
- People on a low-salt diet, or with kidney or heart problems, should check the salt content with a pharmacist.
- Anyone with difficulty swallowing, unintended weight loss, or persistent or worsening symptoms should see a GP rather than self-treat.
Monitoring
- No routine monitoring is needed for short-term use.
- Reviewing symptoms if heartburn keeps returning despite treatment.
- Seeking a GP review for any warning signs such as difficulty swallowing or weight loss.
Side effects
- Side effects are uncommon, as it is not absorbed into the body.
- Occasionally bloating or wind from the foamy raft.
- Rarely, an allergic reaction to one of the ingredients, which needs medical attention.
Key interactions
- It can reduce the absorption of some other medicines, so take them a couple of hours apart.
- Antacid ingredients in the same product can affect medicines such as certain antibiotics and thyroid tablets, so separate the timing.
- Tell the pharmacist about your other medicines if you use alginates regularly.
Available as: Liquid and chewable tablets taken by mouth.
Answers
Alginic acid (alginates): frequently asked questions
What is alginic acid used for?
It is used to relieve heartburn and acid reflux. It forms a protective raft on top of the stomach contents so that acid is less likely to splash back up into the gullet.
When is the best time to take it?
It works best taken after meals and at bedtime, because that is when reflux is most likely and when the protective raft can do the most good.
Can I use it in pregnancy?
Alginates are commonly recommended for heartburn in pregnancy and are generally considered safe, but it is always worth checking with your pharmacist or midwife.
Will it affect my other medicines?
It can reduce how well some other medicines are absorbed, so it is best to leave a couple of hours between an alginate and other tablets.
When should I see a doctor about my heartburn?
See a GP if heartburn keeps coming back, lasts more than a couple of weeks, or comes with difficulty swallowing, weight loss or being sick.
Authoritative sources
- BNF
- NICE CKS
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