Lactulose — NZ Medication Guide
📋 Reviewed by a Registered Pharmacist NZ — This information is for general educational purposes only and does not replace professional medical advice. Always consult your doctor or pharmacist before starting, stopping, or changing any medication.
What is Lactulose?
Lactulose is a synthetic osmotic laxative used to treat constipation and hepatic encephalopathy. This medication is commonly prescribed in New Zealand and is funded by Pharmac for constipation and hepatic encephalopathy.
What is Lactulose Used For?
Lactulose is used for the treatment of chronic constipation (particularly in elderly patients and those taking opioids), and at higher doses for hepatic encephalopathy — a serious complication of liver failure where ammonia builds up in the blood.
How Does Lactulose Work?
Lactulose is a disaccharide (galactose + fructose) that is not absorbed in the small intestine. In the colon, gut bacteria ferment lactulose into short-chain organic acids, increasing osmotic pressure and drawing water into the bowel — softening stools and stimulating peristalsis. In hepatic encephalopathy, lactulose reduces colonic pH, trapping ammonia in the gut and accelerating its excretion.
How to Take Lactulose
For constipation: 15–30 mL (one to two sachets) once or twice daily, adjusted for bowel response. For hepatic encephalopathy: higher doses (up to 30–50 mL three times daily) titrated to produce two to three soft stools per day. Onset of action is 24–48 hours. Mix with water, juice, or food if desired.
Common Side Effects of Lactulose
- Flatulence (gas) and bloating — common initially
- Abdominal cramps
- Nausea
- Diarrhoea (dose-related)
Serious Side Effects — Seek Medical Attention
Contact your doctor or call 111 immediately if you experience any of the following:
- Severe dehydration and electrolyte imbalance (with excessive doses)
- Hypernatraemia (high sodium) in patients restricting fluid intake
Drug Interactions
Lactulose may interact with other medicines. Always inform your doctor and pharmacist of all medications, supplements, and herbal products you are taking. Key interactions include:
- Antibiotics (neomycin and rifaximin can reduce effectiveness in hepatic encephalopathy by altering gut bacteria)
- Antacids (may reduce colonic pH alteration)
New Zealand Prescribing Information
Lactulose solution (3.3 g/5 mL) is funded by Pharmac and widely available in NZ pharmacies. It is the preferred osmotic laxative for constipation in patients taking opioids, in pregnancy (second and third trimester), and for hepatic encephalopathy. Flatulence is common but typically settles after 1–2 weeks of regular use.
Frequently Asked Questions
How long does lactulose take to work?
Lactulose typically takes 24–48 hours to produce a bowel movement. It is not suitable for immediate relief of acute constipation. If you need faster results, speak to your pharmacist about alternative options such as glycerol suppositories or enemas.
Can I take lactulose long-term?
Yes — lactulose is safe for long-term use and is commonly used in patients on chronic opioid therapy, the elderly, and those with chronic liver disease. Regular monitoring of electrolytes is recommended in patients using high doses or who are at risk of dehydration.
⚠️ Disclaimer: This page is for educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your doctor or a qualified health provider with any questions you may have regarding a medical condition or medication. In New Zealand, medication availability and funding may vary — check with Pharmac or your pharmacist for the most current information.
Reviewed by a Registered Pharmacist NZ
References & Further Information
The following New Zealand and international resources were used to inform this page: