> Western Medicines > Lactulose


Used for: Constipation, Hepatic encephalopathy
Chinese name:

What is Lactulose for?

Lactulose is a man-made sugar that is used as a laxative. It works by staying inside your bowel, drawing water into it and softening your stools, making them easier to be removed from your body. Lactulose is used to treat constipation and hepatic encephalopathy. Beneficial effects in hepatic encephalopathy are thought to result from prevention of absorption of ammonia by lowering faecal pH as well as its laxative effect. Lactulose usually begins working within 1-2 days.

How to use it?

Lactulose can be taken by mouth as syrup or solution. The doses for different age groups are listed below but they are not absolute and should be adjusted according to you or your child’s response:



Start with 15 mL twice daily.


Child 1-11 months

2.5 mL twice daily.


Child 1-4 years

2.5-10 mL twice daily.


Child 5-17 years

5-20 mL twice daily.

What are the side effects of Lactulose?

Common side effects of Lactulose include abdominal pain, diarrhoea, flatulence, nausea and vomiting.

Who should not take Lactulose?

People with the following:

  • Galactosaemia
  • Intestinal obstruction
  • Intestinal perforation
  • Risk of intestinal obstruction

Pharmacist Tips:

Lactulose tastes very sweet. You can dilute it with water, milk or fruit juice to make it more palatable. It is not absorbed so it has minimal effect on blood glucose level and can be used by people with diabetes.


Drinking a sufficient amount of water is necessary for lactulose to work efficiently, make sure to stay hydrated. Especially for those who use it for hepatic encephalopathy, who are required by the doctor to make sure more than one passing of stool is achieved per day.


Other laxatives may be needed for immediate relief of constipation. Unlike other laxatives that provide immediate relief, Lactulose can be and is best used regularly.


Common dosing schedule:
You can take Lactulose with or without food.


This schedule is for reference only, adjustments may be made according to individual needs.


Some common medications Lactulose may interact with:

  • Antacids, e.g. Aluminium Hydroxide, may interfere with the desired drop in colonic pH for hepatic encephalopathy

Please notify your doctor or pharmacist if you are taking the above medication, dosage adjustments might be needed.

Where to buy Lactulose in Hong Kong?

In Hong Kong, Lactulose is an over-the-counter medicine which can be purchased without a prescription from any retail outlet in Hong Kong. This includes grocery stores, convenience stores, medicine shops, and pharmacies. It can also be obtained from doctors. To find a pharmacy near you, refer to the list of pharmacies (“Authorized Sellers of Poisons”) from the Hong Kong Department of Health.


For more information about drug names and ingredients, you can visit Hong Kong’s Drug Office at https://www.drugoffice.gov.hk

Need more information?

For detailed information about the use of Lactulose in children, pregnancy and breastfeeding, and for questions about drug interactions, please check with your pharmacist or doctor.

Disclaimer: our goal is to provide you with the most relevant drug information and common dosage for Hong Kong. This information does not constitute medical advice. For specific treatment recommendations and advice, always discuss with your doctor or pharmacist, and follow the instructions included with your specific medicine.

Brands in Hong Kong
Available dosage
  • 667g/l (Oral Solution)
Drug class
Sub class
Osmotic Laxatives
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Used for: Constipation, Hepatic encephalopathy
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