lactulose at a glance
Medicine class
Osmotic laxative
Main use
Softens stools to relieve constipation
How it is supplied
A sweet oral solution in bottles or single-use sachets, depending on the product
Onset
Its effect is gradual rather than immediate
What is lactulose used for?
Licensed uses differ between products.
Constipation: both selected products are licensed to treat constipation.
Hepatic encephalopathy, including hepatic coma: licensed for the selected bottled oral solution, but not the selected constipation-only sachets.
How does lactulose work?
Lactulose passes to the colon, where bacteria convert it into organic acids. This draws water into the bowel, increases stool water content and supports bowel movement. In hepatic encephalopathy, changes in colonic acidity, transit and bacterial nitrogen handling help reduce intestinal ammonia absorption and increase nitrogen removal in stool.
lactulose preparations and strengths
Oral solution
Route: Oral
Strengths: 3.335 g/5 mL, 10 g/15 mL
How to take lactulose
Follow the pack label or prescriber's instructions and use the supplied measuring device for bottled solution.
Take it with or without food.
It may be swallowed undiluted or mixed with water or fruit juice if the sweet taste is difficult.
Swallow it promptly rather than holding it in the mouth.
Maintain adequate fluid intake unless a clinician has advised fluid restriction.
Use sachet contents immediately after opening and discard any remainder.
lactulose side effects
Common or expected effects
- Diarrhoea
- Wind and bloating
- Abdominal discomfort or pain
- Nausea or vomiting
Get urgent medical advice
- Severe or persistent diarrhoea or vomiting causing dehydration or electrolyte disturbance
- Hypersensitivity reactions, including rash, hives or swelling
- Signs of anaphylaxis, such as throat swelling or breathing difficulty
lactulose in pregnancy
Lactulose can be used during pregnancy when needed. Its systemic absorption is negligible, and available information does not suggest harm to the baby. Discuss persistent constipation, severe abdominal symptoms or ongoing treatment with a midwife, pharmacist or prescriber.
lactulose while breastfeeding
Lactulose can be used while breastfeeding because maternal absorption and expected transfer into milk are very low. As a precaution, seek advice if the baby develops diarrhoea, vomiting, irritability or feeding difficulties.
lactulose interactions
Important interactions are uncommon, but some are product-specific and become more relevant if lactulose causes diarrhoea or electrolyte loss.
Thiazide diuretics, corticosteroids or amphotericin B
The constipation-only sachet product warns that lactulose may add to potassium loss caused by these medicines.
Cardiac glycosides, such as digoxin
Potassium depletion may increase their effects and toxicity risk.
Colon-released pH-dependent medicines, such as some 5-aminosalicylate products
Reduced colonic pH may interfere with release or activity; check the specific formulation.
Common questions about lactulose
Answers are fully visible for fast scanning and source review.
How long does lactulose take to work?
It works gradually and may take a couple of days to produce its full laxative effect.
Can lactulose be mixed with water or juice?
Yes. The oral solution may be diluted with water or fruit juice to make the sweet taste easier to tolerate.
Sources
These sources were used to prepare and review this medicine page.
Prepared and reviewed by the iatroX editorial team.