Sounds like 'lak-tew-lows'

Lactulose is a laxative used to treat and prevent constipation. Find out how to take it safely and possible side effects. Lactulose is also called Laevolac.

Type of medicine Also called
  • Laxative 
  • To treat constipation
  • Laevolac 

What is lactulose?

Lactulose is a type of laxative that helps to produce a soft bowel motion (poo). It is used to treat constipation in adults and children. Read more about constipation in adults and constipation in children. 

There are many different types of laxatives. Lactulose is referred to as an osmotic laxative, which means that it works by drawing water into your bowel. The bowel becomes filled with extra fluid, which makes the muscles of the bowel contract and squeeze the poo along, causing a bowel motion. Read more about types of laxatives.

Lactulose is also used for people with a liver problem called hepatic encephalopathy. Lactulose changes the acidity of your poos, which stops the growth of bacteria that produce ammonia in your bowel and in this way reduces the production of ammonia in your gut. 

In New Zealand lactulose comes as a liquid syrup called Laevolac. 

Dose of lactulose

The dose of lactulose will be different for different people.

  • Constipation: The usual dose in adults is 15 mL 2 times a day. The dose for children will depend on their age. It is usually given 2 times a day.
  • Liver problems: The usual dose is 30–50 mL 3 times a day.
  • Always take your lactulose exactly as your doctor or pharmacist has told you. The label on your medicine will tell you how much lactulose to take, how often to take it and any special instructions.

How to take lactulose

  • Try to space your doses evenly throughout the day, eg, if taken 2 times a day, take it in the morning and evening.   
  • Take lactulose as directed with a glass of water.
  • Lactulose is sweet and can be mixed with other liquids, such as water, milk or fruit juice.
  • If you forget to take a dose, just take the next dose when it is due. Do not take two doses together to make up for a forgotten dose.

When should the medicine start working?

Lactulose does not work straight away. When used for constipation, it can take a day or 2 before lactulose softens the poos enough to pass them comfortably. However, if after several days you do not feel your symptoms are improving, or if they get worse, ask your doctor or pharmacist for advice.

Precautions before taking lactulose

  • Are you lactose intolerant?
  • Do you have other stomach or bowel problems?
  • Are you pregnant or breastfeeding?
  • Do you have diabetes?

If so, it’s important that you tell your doctor before you start taking lactulose. Sometimes a medicine isn’t suitable or it can only be used with extra care.

What are the side effects of lactulose?

Like all medicines, lactulose can cause side effects, although not everyone gets them. Often side effects improve as your body adjusts to the new medicine.

Side effects What should I do?
  • Bloating (wind or gas)
  • Tummy ache
  • Stomach discomfort
  • It is quite common for lactulose to cause bloating or gas. 
  • Tell your doctor if troublesome.
  • Feeling sick (nausea)
  • Try having lactulose with some water or fruit juice or with meals.
  • Signs of dehydration such as feeling weak, very thirsty and headache
  • Tell your doctor.
Did you know that you can report a side effect to a medicine to CARM (Centre for Adverse Reactions Monitoring)? Report a side effect to a product

Learn more

The following links have more information on lactulose. 

Lactulose (adults) New Zealand Formulary
Lactulos (children) New Zealand Formulary


  1. Lactulose New Zealand Formulary
  2. Lactulose New Zealand Formulary for Children
  3. Managing constipation in older adults BPAC, NZ, 2019
Credits: Sandra Ponen, Pharmacist. Reviewed By: Angela Lambie, Pharmacist, Auckland Last reviewed: 27 Sep 2019