Lactulose can take up to 48 hours to act.

If you find lactulose makes you feel queasy, mix your dose with some water or fruit juice. Alternatively, take it after a meal.

About lactulose

Type of medicine Osmotic laxative
Used for Constipation
Also called Duphalac®, Lactugal®
Available as Oral liquid

Constipation is a common problem. It means either going to the toilet less often than usual to empty your bowels, or passing hard or painful stools. Constipation may be caused by not eating enough fibre or not drinking enough fluids. Pregnancy, a lack of exercise or movement (such as being ill in bed) and some medicines, including some painkillers, can also cause constipation.

Often, increasing the amount of fibre in your diet (such as by eating more fruit, vegetables, cereals, and wholemeal bread) and drinking plenty of water each day can effectively prevent or relieve constipation. You will have been given lactulose for constipation if you cannot increase the fibre in your diet or if this is insufficient. Lactulose works by drawing fluid into your bowel, which makes your stools softer and easier to pass.

Lactulose also changes the acidity of your stools which helps discourage the growth of some bacteria in the bowel. This is helpful in treating a liver problem called hepatic encephalopathy.

Before taking lactulose

Before taking lactulose make sure your doctor or pharmacist knows:

  • If you are so constipated that you think you may have a blockage.
  • If you have galactosaemia (this means your body cannot process galactose which is a type of sugar).
  • If you are lactose intolerant (unable to digest milk sugar).
  • If you are pregnant or breast-feeding. (Lactulose may be used during pregnancy and breast-feeding, but it is important that your doctor or pharmacist knows about this.)
  • If you are taking other medicines, including those available to buy without a prescription, herbal and complementary medicines.
  • If you have ever had an allergic reaction to this or to any other medicine.

How to take lactulose

  • Before starting this treatment, read the manufacturer's printed information leaflet from the pack. The leaflet will give you more information about the specific brand of lactulose you have been given, and any possible side-effects from taking it.
  • Take lactulose exactly as you have been told to. Your doctor or pharmacist will tell you how much to take and when to take it. Your dose will also be on the label of the bottle. The usual starting dose for an adult is 15 ml (three 5 ml spoonfuls) twice daily, although the dose you are advised to take may be different from this as it will be adjusted to suit your needs.
  • You can mix lactulose with water or fruit juice to improve the taste. This should be done just before you take a dose. Alternatively, try taking lactulose after meals, to help prevent any feelings of queasiness.
  • Lactulose should not be taken by children unless it is on the advice of a doctor or a healthcare professional experienced in the management of constipation in children. Check the label carefully to make sure you are giving the correct dose for the age of your child.
  • If you forget to take a dose, do not worry, just take the next dose when it is due. Do not take two doses together to make up for a forgotten dose.

Getting the most from your treatment

  • Lactulose can take up to 48 hours to act, so it may take two or three days before you feel the full benefit. However, if after a week you do not feel your symptoms are improving, or if they get worse, speak with your doctor.
  • It is important to drink plenty while you are constipated. You should aim to drink at least two litres (about 8-10 cups) of fluid per day. Most sorts of drink will do, but as a start, try just drinking a glass of water 3-4 times a day in addition to what you normally drink.
  • Try to eat a balanced diet containing high-fibre foods such as wholemeal and whole-grain breads and cereals, fruit and vegetables, brown rice and wholemeal pasta. If you are not used to a high-fibre diet, it may be best to increase the amount of fibre you eat gradually.
  • Keeping your body active will help you to keep your digestive system moving, so try to take some regular daily exercise.
  • You may wish to include some foods that contain sorbitol in your diet. Sorbitol is a naturally occurring sugar. It is not digested very well and draws water into your bowel, which has an effect of softening stools. Fruits (and their juices) that have a high sorbitol content include: apples, apricots, gooseberries, grapes (and raisins), peaches, pears, plums, prunes, raspberries and strawberries.

Can lactulose cause problems?

Along with their useful effects, most medicines can cause unwanted side-effects although not everyone experiences them. These usually improve as your body adjusts to the new medicine, but speak with your doctor or pharmacist if any of the following side-effects continue or become troublesome.

Possible lactulose side-effects What can I do if I experience this?
Abdominal cramps and discomfort Try taking lactulose after food
Feeling or being sick Try taking lactulose after food, or mixing your dose with some water or fruit juice
Flatulence (excess wind) This usually settles down after a few days

If you experience any other symptoms which you think may be due to this medicine, speak with your doctor or pharmacist.

How to store lactulose

  • Keep all medicines out of the reach and sight of children.
  • Store in a cool, dry place, away from direct heat and light. Do not store lactulose in a refrigerator.