Lactulose is a laxative taken to treat constipation (difficulty pooing).
It's also taken to help a condition caused by 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.
Who can take lactulose
Most adults and young people aged 14 years and over can take lactulose.
Babies and children aged under 14 can take lactulose if their doctor recommends it. Do not give lactulose to a child under the age of 14 unless their doctor has said it's OK.
Who may not be able to take lactulose
Lactulose is not suitable for some people. To make sure it's safe for you, tell your doctor or pharmacist if you:
- have ever had an allergic reaction to lactulose or any other medicine
- 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 if you need to take high doses for a long time to treat hepatic encephalopathy
- have irritable bowel syndrome (IBS), as lactulose increases gas and bloating in the stomach, which can make IBS worse
Your dose of lactulose can go up or down, depending on how well the medicine is working.
The usual dose for constipation is:
- adults – 15ml, taken twice a day as a starting dose
- children aged 5 to 17 years – 5ml to 20ml, taken twice a day
- children aged 1 to 4 years – 2.5ml to 10ml, taken twice a day
- babies aged 1 month to 11 months – 2.5ml, taken twice a day
For adults with hepatic encephalopathy, the usual dose is between 30ml and 50ml, taken 3 times a day.
Only give lactulose to a child under 14 years if their doctor recommends it.
You can take lactulose with or without food.
The medicine comes with a plastic cup or spoon to measure your dose. If you do not have a cup or spoon, ask your pharmacist for one. Do not use a kitchen spoon as it will not measure the right amount.
Some people do not 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 water or other liquid during the day while you're taking lactulose or your constipation may get worse.
How long to take it for
You can take lactulose for as long as your constipation lasts, or for as long as your doctor has recommended. This will usually be for up to a week.
For more severe constipation, and if you're taking lactulose for hepatic encephalopathy, your doctor may recommend that you take it for many months.
If you forget to take it
If you forget a dose of lactulose, just skip the missed dose and take your 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.
If you take too much
Taking an extra dose of lactulose is unlikely to harm you. You may get diarrhoea and stomach pain but this should get better within a day or two.
If you're worried, talk to your doctor or pharmacist for advice.
Common side effects
A very common side effect of lactulose, particularly at high doses, is diarrhoea. This happens in more than 1 in 10 people.
These other common side effects happen in more than 1 in 100 people. There are things you can do to help cope with them:
These side effects are mild and usually go away after a couple of days. Talk to your doctor or pharmacist if the advice on how to cope does not help and side effects bother you or do not go away.
Serious side effects
It happens rarely (less than 1 in 100 people), but some people have serious side effects when taking lactulose.
Call a doctor or contact 111 straight away if you have severe diarrhoea or vomiting for more than a couple of days and you get:
- muscle cramps or weakness
- an irregular heartbeat
This could be a sign of an electrolyte imbalance, where levels of substances like sodium, potassium and magnesium in your body get too high or too low.
Go to 111.nhs.uk or call 111
Serious allergic reaction
In rare cases, it's possible to have a serious allergic reaction (anaphylaxis) to lactulose.
These are not all the side effects of lactulose. For a full list see the leaflet inside your medicines packet.
Lactulose and pregnancy
Lactulose can be taken during pregnancy and is not harmful to your baby.
Lactulose and breastfeeding
If your doctor or midwife says your baby is healthy, it's OK to take lactulose while you are breastfeeding.
Lactulose does not pass into breast milk so it's very unlikely to cause any side effects in your baby. However, it is always better to treat constipation without taking a medicine first.
If your baby is not feeding as well as usual, or has diarrhoea, or if you have any other concerns about your baby, then talk to your health visitor, midwife, pharmacist or doctor.
Lactulose and fertility
There's no evidence to suggest that taking lactulose should cause any fertility problems in either men or women.
Cautions with other medicines
There are no known problems mixing lactulose with other medicines or herbal remedies.
Taking lactulose with other laxatives
For most people, 1 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's an increased risk of side effects.
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