Gastrointestinal
Laxatives
Drugs for constipation — Different types for different problems — chosen by cause and stool consistency.
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
Laxatives treat and prevent constipation. The main groups are bulk-forming, osmotic, stimulant and stool-softening agents, each suited to a different cause or stool type.
How it works
Bulk-forming agents add fibre that holds water and increases stool bulk; osmotic agents draw water into the bowel to soften stool; stimulants speed up bowel muscle activity; and softeners help water mix into hard stool.
In practice
In practice laxatives are chosen by type rather than habit: a bulk-forming agent suits a low-fibre diet (with plenty of fluid), an osmotic such as a macrogol softens hard stool, and a stimulant helps a sluggish bowel — while a softener-plus-stimulant combination is standard for opioid-induced constipation. We also look first for reversible causes (drugs, dehydration, low fibre) and avoid bulk-forming agents where there is any suggestion of obstruction. The aim is comfortable, regular stools, then stepping the dose down.
Examples
Practical use
How to take it & use it well
- Choose and take your laxative as advised, and drink plenty of fluids, especially with bulk-forming types such as ispaghula.
- Take a bulk-forming laxative with water and not just before bed, to avoid it swelling in the throat or gullet.
- Some, such as macrogol, are mixed with water before drinking; follow the product instructions.
- Stimulant laxatives like senna often work overnight, so they are commonly taken in the evening.
- Use stimulant laxatives short-term where possible, and see your GP if constipation persists or you notice blood or a sudden change in bowel habit.
Common uses
- Short-term and chronic constipation
- Opioid-induced constipation (softener plus stimulant)
- Bowel preparation and faecal impaction (specific regimens)
Monitoring
- Bowel response and stool consistency
- Fluid intake, particularly with bulk-forming agents
- Underlying or reversible causes
Weighing it up
Advantages & disadvantages
Advantages
- They relieve constipation and make passing stools easier and more comfortable.
- Different types suit different needs, from gentle softening to more active stimulation.
- Many are available without prescription for short-term use.
- They can prevent straining, which is helpful after surgery, in pregnancy or with painful conditions like piles.
Disadvantages
- They can cause cramping, bloating or wind.
- Overuse of stimulant types can lead to reliance and a sluggish bowel.
- Bulk-forming types need plenty of fluid and can worsen things if fluid intake is low.
- They can occasionally cause diarrhoea or changes in body salts if overused.
Key safety principles
What to watch for
- Avoid bulk-forming laxatives if bowel obstruction is suspected, and take them with plenty of fluid.
- Match the type to the problem; review prolonged stimulant use.
- Always anticipate and treat opioid-induced constipation proactively.
Key interactions
What to avoid or check alongside
- Bulk-forming laxatives can reduce the absorption of some medicines if taken at the same time, so space them apart.
- Overusing stimulant laxatives can lower potassium, which may increase the risk from digoxin and some heart-rhythm medicines.
- Lactulose and some others can affect how certain medicines are absorbed from the gut.
- Combining several laxatives can cause excessive diarrhoea and fluid or salt loss.
- Low potassium from laxative overuse can add to the effects of water tablets and steroids.
Patient & carer advice
- Drink plenty of fluid, especially with fibre-based laxatives
- Increase dietary fibre and activity where you can
- If you take strong painkillers, expect to need a laxative regularly
Answers
Laxatives: frequently asked questions
Which laxative should I use for constipation?
It depends on the cause and your needs. Bulk-forming types add fibre, osmotic types like macrogol and lactulose draw in water to soften stools, and stimulants like senna prompt the bowel to move. A pharmacist can advise.
Can I use laxatives every day?
Some, such as bulk-forming and osmotic types, can be used regularly under guidance. Stimulant laxatives are best for short-term use, as overuse can make the bowel rely on them.
Why do bulk-forming laxatives need plenty of water?
They work by absorbing water to bulk and soften the stool. Without enough fluid they can cause blockage or make constipation worse, so take them with plenty of water.
When does a stimulant laxative work?
Stimulant laxatives such as senna usually take several hours and often work overnight, which is why they are commonly taken in the evening.
When should constipation be checked by a doctor?
See your GP if constipation is persistent, comes with blood in the stool, unexplained weight loss, severe pain, or a sudden change in your normal bowel habit.
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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