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Dr Karen Martin
Reviewed by Dr Karen MartinReviewed on 19.10.2023 | 3 minutes read

Lactulose is an oral solution used to treat constipation on prescription only. It comes as a sugar-like syrup and is suitable for adults and children.

Doctor’s advice

Who is it for?

It is for short-term relief of constipation when other treatments have not worked. Initial treatment should include simple measures like incorporating fruit, vegetables, and foods high in fiber into your diet, increasing your exercise, and drinking plenty of water.

Fybogel sachets should be your first option when moving on to specific constipation products. If you've had no luck with any of these measures, Movicol or lactulose are your options and work similarly.

Lactulose is suitable for all ages and does not interact with most medications. It's safe for pregnancy and breastfeeding.

It's one of the preferred laxatives for constipation related to strong opioid painkillers, such as codeine or morphine. However, it's only for short-term relief, so if you're on these medications in the long term, Movicol will be a safer option unless your doctor advises you differently.

How does it work?

Lactulose is a synthetic sugar molecule that works as an osmotic laxative, meaning – in broad terms – it draws water into the small intestine, early on in the digestive system while stool moves along. This helps stool on its way by making it softer and easier to pass.

In the latter part of the intestine, normal gut bacteria work alongside to encourage more water to be drawn into the bowel, further encouraging bowel movements.

Sodium chloride, sodium bicarbonate, and potassium chloride are components in Movicol to support the electrolyte balance, which is why it's a more suitable choice in the long term compared to lactulose.

As lactulose relies on drawing water out of other parts of the body and into the bowel, you need to make sure you're drinking plenty of water to ensure it's working at its best and that you don't get dehydrated.

Any reason to avoid it?

You should take lactulose with caution if you have diabetes, as this is a form of sugar that may affect your sugar levels at high doses, or if you have poorly controlled diabetes or take insulin. However, since lactulose is not absorbed and the amount of sugar produced is small, normal doses for constipation should not affect blood sugar levels greatly.

You can discuss which laxative is best in people with diabetes with your doctor. Movicol may be a good option as it works similarly but doesn't disrupt sugar levels. You can discuss which laxative is best in people with diabetes with your doctor.

Lactulose is only for short-term use, so if you have been using it regularly, it's worth speaking to your doctor about it to solve the underlying cause and consider a laxative for long-term use, such as Movicol.

You should be cautious if you are lactulose-intolerant and avoid lactulose if you have galactosemia or any holes or perfusions in the intestines.

Lactulose is suitable for children aged over 1 year but needs to be prescribed by a doctor.

Are there any side effects?

Most people tolerate the medicine very well, however, some people may experience side effects, including abdominal pain, diarrhea, flatulence, nausea and vomiting. These are normally caused by the fermentation process with bacteria in the gut.

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This article has been written by UK-based doctors and pharmacists, so some advice may not apply to US users and some suggested treatments may not be available. For more information, please see our T&Cs.
Dr Karen Martin
Reviewed by Dr Karen Martin
Reviewed on 19.10.2023
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