Gastrointestinal
Antacids and alginates
Indigestion and reflux remedies — Fast, on-demand relief for heartburn and indigestion — often the sensible first step.
Education and reference only. This is a plain-language class overview — it deliberately contains no doses. Always check the current Summary of Product Characteristics (SmPC), the BNF and your local formulary before prescribing or administering any medicine.
What it is
Antacids neutralise stomach acid for quick symptom relief, while alginates form a protective "raft" that floats on the stomach contents to reduce reflux. Both are widely available for heartburn and indigestion.
How it works
Antacids chemically neutralise acid that is already in the stomach, giving rapid but short-lived relief. Alginates react with stomach acid to create a gel raft that physically blocks acid from refluxing into the gullet.
In practice
In practice antacids and alginates are the simple, fast-acting first line for occasional heartburn and indigestion, working within minutes and ideal taken after meals and at bedtime. The practical catches are timing and interactions: they can reduce the absorption of several other medicines (such as some antibiotics, levothyroxine and iron), so they should be separated by a couple of hours. Persistent symptoms, or any alarm features, mean stepping up to acid-suppression and considering investigation rather than continued self-treatment.
Examples
Practical use
How to take it & use it well
- Take them when symptoms occur or after meals and at bedtime, as advised for your product.
- Separate them from your other medicines by leaving a clear gap, as they can reduce how well other tablets are absorbed.
- Alginate products work best taken after eating, as they form a protective raft on top of the stomach contents.
- Shake liquid forms before use and use the measure provided.
- If you need them most days, or symptoms continue, see your GP to look into the cause.
Common uses
- Occasional heartburn and indigestion
- Reflux symptoms, especially after meals or lying down
- On-demand relief alongside longer-term acid suppression
Monitoring
- Symptom relief and frequency of use
- Review if needed regularly or symptoms persist
- Renal function where high or prolonged use
Weighing it up
Advantages & disadvantages
Advantages
- They give fast relief from heartburn and indigestion.
- Alginates form a barrier that helps stop acid rising into the gullet.
- They are available without prescription for occasional use.
- They are generally safe for short-term symptom relief.
Disadvantages
- Their effect is short-lived compared with acid-suppressing medicines.
- They can interfere with the absorption of many other medicines if taken too close together.
- Some can cause constipation or diarrhoea depending on their ingredients.
- Products containing sodium may not suit people who need to limit salt.
Key safety principles
What to watch for
- Can reduce absorption of other drugs (e.g. some antibiotics, levothyroxine, iron) — separate doses by about two hours.
- Magnesium salts can loosen and aluminium salts can constipate; caution with high sodium content in some products.
- Caution in renal impairment with magnesium- and aluminium-containing products.
Key interactions
What to avoid or check alongside
- They reduce the absorption of certain antibiotics, such as tetracyclines and fluoroquinolones, if taken close together.
- They can lower the absorption of iron and of thyroid medicine like levothyroxine, so these should be spaced apart.
- By raising stomach pH they can affect medicines designed to dissolve in a certain part of the gut.
- They can reduce the effect of some bisphosphonates used for bones if not separated in time.
- Spacing antacids and alginates from other medicines by a clear interval helps avoid these problems.
Patient & carer advice
- Take after meals and at bedtime for predictable symptoms
- Leave a couple of hours between these and your other medicines
- See us if you need them most days, or have weight loss or swallowing problems
Answers
Antacids and alginates: frequently asked questions
What is the difference between an antacid and an alginate?
An antacid neutralises stomach acid for quick relief, while an alginate forms a floating raft over the stomach contents to help stop acid rising into the gullet. Many products combine both.
Why should I separate antacids from other medicines?
They can bind to or change the absorption of many medicines, making them less effective. Leaving a clear gap between them helps your other medicines work properly.
When should I take an alginate?
Alginates work best taken after meals and at bedtime, as they form their protective raft on top of food in the stomach.
Can antacids cause bowel problems?
Yes. Depending on the ingredients, some can cause constipation and others diarrhoea. Combination products are designed to balance this, but tell your pharmacist if you have problems.
When should I see a doctor for indigestion?
See your GP if you need antacids most days, symptoms persist, or you have difficulty swallowing, weight loss, vomiting or black stools, as these need further checks.
Authoritative sources
Always verify against the source
This overview is for orientation. For doses, interactions, contra-indications and the full monograph, use:
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