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  1. About lactulose
  2. Key facts
  3. Who can and can't take lactulose
  4. How and when to take it
  5. Side effects
  6. How to cope with side effects
  7. Pregnancy and breastfeeding
  8. Cautions with other medicines
  9. Common questions

1. About lactulose

Lactulose is a laxative taken to treat constipation (difficulty pooing). It is also taken to help a severe liver disease called hepatic encephalopathy.

Lactulose comes as a sweet syrup that you swallow.

It's available on prescription and to buy from pharmacies.

Do not give lactulose to children under 14 years unless recommended by a doctor.

2. Key facts

  • Lactulose relieves constipation by drawing water into the bowel to make poo softer.
  • The most common side effects are diarrhoea, bloating and wind. These are usually mild and shortlived.
  • Lactulose takes at least 48 hours to work.
  • If you find the taste of lactulose too sweet, you can dilute it with fruit juice or water.
  • Lactulose is also called by the brand names Duphalac and Lactugal.

3. Who can and can't take lactulose

Lactulose can be taken by adults including pregnant and breastfeeding women. It can also be taken by children aged 14 years and over.

Babies and children can take lactulose if their doctor recommends it. Do not give lactulose to a child under the age of 14 years unless your doctor has said so.

Lactulose isn't suitable for some people. To make sure lactulose is safe for you, tell your doctor or pharmacist if you:

  • have ever had an allergic reaction to lactulose or any other medicine in the past
  • can't digest a sugar called lactose (lactose intolerance)
  • have a rare health problem where the body cannot process a sugar called galactose (galactosaemia)
  • have diabetes (as lactulose may affect your blood sugar levels)

4. How and when to take it

Take lactulose once or twice a day. You can take it with or without food.

How much to take

Your dose of lactulose can go up or down, depending on how well the medicine is working.


Only give lactulose to children under 14 years if their doctor recommends it.

For constipation in:

  • adults – the starting dose is usually 15ml taken twice a day
  • children aged 5 to 17 years - the usual dose is 5ml to 20ml twice a day
  • children aged 1 to 4 years – the usual dose is 2.5ml to 10ml twice a day
  • babies aged 1 to 11 months – the usual dose is 2.5ml twice a day

For adults with hepatic encephalopathy, the usual dose is between 30ml and 50ml taken 3 times a day.

How to take it

The medicine comes with a plastic cup or spoon to measure your dose. Do not use a kitchen spoon as it will not give the right amount. If you don't have a cup or spoon, ask your pharmacist for one.

Some people don't like the sweet taste of lactulose. To improve the taste, you can mix your dose with half a glass or water or fruit juice.

Aim to drink 6 to 8 glasses of fluid during the day while you are taking lactulose or your constipation may get worse.

What if I forget to take it?

If you forget a dose of lactulose, don't worry, just take the next dose at the usual time.

Never take 2 doses at the same time. Never take an extra dose to make up for a forgotten one.

If your doctor has told you to take lactulose every day and you often forget doses, it may help to set an alarm to remind you. You could also ask your pharmacist for advice on other ways to help you remember to take your medicine.

What if I take too much?

Taking an extra dose of lactulose by accident is unlikely to harm you. You may get diarrhoea and stomach pain but this should ease off within a day or two.

If you're worried, talk to your doctor or pharmacist for advice.

5. Side effects

Like all medicines, lactulose may cause side effects in some people, but many people have no side effects or only minor ones.

Common side effects

A very common side effect, particularly at high doses, is diarrhoea. This happens in more than 1 in 10 people.

Other common side effects, which happen in more than 1 in 100 people, are:

  • bloating
  • wind (farting and burping)
  • feeling sick
  • being sick (vomiting)
  • stomach pain

These side effects are mild and usually go away after a couple of days. Talk to your doctor or pharmacist if the side effects bother you or don't go away.

Serious side effects

Call a doctor straight away if these unlikely but serious side effects happen to you:

  • severe diarrhoea or vomiting
  • muscle cramps or weakness
  • irregular heartbeat

Serious allergic reaction

In rare cases, it's possible to have a serious allergic reaction (anaphylaxis) to lactulose.

Immediate action required: Call 999 or go to A&E if:

  • you get a skin rash that may include itchy, red, swollen, blistered or peeling skin
  • you're wheezing
  • you get tightness in the chest or throat
  • you have trouble breathing or talking
  • your mouth, face, lips, tongue or throat start swelling

You could be having a serious allergic reaction and may need immediate treatment in hospital.

These are not all the side effects of lactulose. For a full list see the leaflet inside your medicines packet.


You can report any suspected side effect to the UK safety scheme.

6. How to cope with side effects

What to do about:

  • diarrhoea - drink lots of fluids, such as water or squash, to avoid dehydration. Signs of dehydration include peeing less than usual or having dark strong-smelling pee. Reducing your dose of lactulose may also help diarrhoea. Do not take any other medicines to treat diarrhoea without speaking to a pharmacist or doctor.
  • bloating - take lactulose between meals instead of before or after them
  • wind - steer clear of foods that cause wind like lentils, peas, beans and onions. It might also help to eat smaller and more frequent meals, eat and drink slowly, and exercise regularly. Some pharmacy remedies help wind, such as charcoal tablets or simethicone.
  • feeling sick - try taking lactulose with meals, or mixing your dose with some water or fruit juice
  • being sick (vomiting) - drink lots of fluids, such as water or squash, to avoid dehydration. Take small, frequent sips. Do not take any other medicines to treat vomiting without speaking to a pharmacist or doctor.
  • stomach pain - try to rest and relax. It can help to eat and drink slowly and have smaller and more frequent meals. Putting a heat pad or covered hot water bottle on your stomach may also help. If you are in a lot of pain, speak to your pharmacist or doctor.

7. Pregnancy and breastfeeding

Lactulose is generally safe to take during pregnancy and while breastfeeding.

Constipation is common at the end of pregnancy and just after having a baby.

If you're pregnant or breastfeeding, it's always better to try to safely treat constipation without taking a medicine.

Your doctor or midwife will first advise you to eat more fibre and drink plenty of fluids. You'll also be encouraged to do gentle exercise.

If dietary and lifestyle changes don't work, you may be recommended a laxative such as lactulose.

For more information about how laxatives can affect you and your baby during pregnancy, read this leaflet on the Best Use of Medicines in Pregnancy (BUMPS) website.


Tell your pharmacist or doctor if you're trying to get pregnant, are already pregnant or if you're breastfeeding.

8. Cautions with other medicines

There are no known problems mixing lactulose with other medicines or herbal remedies.


For safety, tell your doctor or pharmacist if you're taking any other medicines, including herbal remedies, vitamins or supplements.

9. Common questions

How does lactulose work?

Lactulose is broken down in the bowel into products that pull water out from the body and into the bowel to soften poo and make it easier to pass. It's called an osmotic laxative.

People with liver disease can sometimes get problems in their brain (hepatic encephalopathy). This happens because the liver isn't clearing toxins properly. In this situation, lactulose clears the bowels and helps the body remove the toxins that build up when the liver is failing.

When will I feel better?

It takes a couple of days for lactulose to work.

Talk to your doctor if you are still constipated after 3 days.

How long should I take lactulose for?

You can take lactulose for as long as the constipation lasts, or for as long as your doctor has recommended. This will usually be for up to a week.

For more serious constipation, and if you are taking lactulose for hepatic encephalopathy, your doctor may recommend that you take it for many months.

Is it safe to take lactulose for a long time?

Ideally, you should only take lactulose occasionally and for a few days at a time. Using laxatives like lactulose for longer can lead to prolonged diarrhoea. It can also cause an electrolyte imbalance, where levels of substances like sodium, potassium and magnesium in your body get too high or too low. An electrolyte imbalance can cause serious health problems such as muscle spasm and twitching and even convulsions.

However, there are some situations where you may need to take lactulose for many months, for instance, if you keep getting constipation or if you have a health problem called hepatic encephalopathy. In this instance, your doctor will decide exactly how long and how much lactulose you need to take.

Can I take different laxatives together?

For most people, one laxative will be enough to relieve constipation.

Occasionally, you may need to take 2 different types of laxatives at the same time to get your bowels moving again. Only take 2 laxatives together on the advice of your doctor or pharmacist as there is an increased risk of side effects.

Are other laxatives any better?

There are other types of laxatives. They work in a different way to lactulose but are equally good at treating constipation. Some work more quickly than lactulose.

  • Bulk-forming laxatives, for example Fybogel and methylcellulose. These increase the "bulk" or weight of poo which in turn stimulates bowel movement. They take 2 or 3 days to work.
  • Stimulant laxatives, for example, senna and bisacodyl. These speed up your bowels by stimulating the nerves that control the muscles lining your gut. They work more quickly than other laxatives. If you take them at bedtime, they work overnight.
  • Surface-wetting laxatives, for example arachis oil and docusate sodium. These let water get into poo to soften it and make it easier to pass.
Can people with IBS take it?

It's not a good idea for people with irritable bowel syndrome (IBS) to take lactulose.

Lactulose increases gas and bloating in the stomach, which can make IBS worse. Other types of laxative may be more suitable if you have IBS.

Can people with diabetes take it?

Yes, usually they can. If you have diabetes, ask your doctor or pharmacist whether this medicine is suitable you.

If you have diabetes and are taking normal doses of lactulose for constipation, the medicine will have little, if any, effect on your blood sugar levels.

However, if you have diabetes and need to take high doses of lactulose for many months, the medicine may affect your blood sugar levels. In this case, monitor your blood sugar levels carefully and share the results with your doctor. Your diabetes treatment or diet may need to be adjusted.

People with diabetes often think that lactulose is the same as lactose - a sugar that can dangerously raise blood sugar levels. But lactulose is very different. It's a manmade sugar that is broken down in the bowel so very little gets into the bloodstream.

Will it affect my fertility?

There's no firm evidence to suggest that taking lactulose will reduce fertility in either men or women.

Will it affect my contraception?

Lactulose doesn't affect any type of contraception including the combined pill or emergency contraception unless you have severe diarrhoea (6 to 8 watery poos in 24 hours) for more than 24 hours.

If you have severe diarrhoea your contraceptive pills may not protect you from pregnancy. Look on the pill packet to find out what to do.

Read more about what to do if you're on the pill and you're vomiting or have diarrhoea.

Is there any food and drink I need to avoid?

You can eat and drink normally while taking lactulose.

It might be a good idea to stop eating pastries, puddings, sweets, cheese and cake for a while as these foods can make constipation worse.

Can I drink alcohol with it?

Yes, you can drink alcohol with lactulose.

Can I use lactulose after surgery?

It's quite common to have constipation after surgery. Using a laxative may help relieve the discomfort.

If you have constipation after an operation, it's fine to use lactulose syrup. It's gentler on the tummy muscles than some other types of laxative, like senna.

Can lifestyle changes help constipation?

It's often possible to improve constipation without laxatives. Before trying lactulose or to stop constipation coming back it may help to:

  • get more fibre into your diet - aim for about 30g of fibre a day. High-fibre foods include fruit, vegetables and cereals. If you are not used to a high-fibre diet, increase the amount of fibre you eat gradually.
  • add bulking agents, such as wheat bran, to your diet. These will help make your poo softer and easier to pass (although bran and fibre can sometimes make bloating worse).
  • drink plenty of water - to keep poo soft
  • exercise regularly - keeping your body active will help to keep your gut moving