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Dr Roger Henderson
Reviewed by Roger HendersonReviewed on 29.04.2024 | 3 minutes read

Lactulose is an over-the-counter oral solution used to treat constipation in the short term. 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. You should first try simple measures like incorporating fruit, vegetables and foods high in fibre 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 next options and work in similar ways.

Lactulose is suitable for all ages and agrees with most medication. It’s safe in pregnancy and breastfeeding.

It's one of the preferred laxatives if you have constipation related to strong opioid painkillers, such as co-codamol, codeine or morphine. This should be taken primarily instead of trying Fybogel or other sachets. 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 later part of the intestine, normal gut bacteria work alongside to encourage more water to be drawn into the bowel, further encouraging bowel movements.

The sodium chloride, sodium bicarbonate and potassium chloride present in movicol or similar macrogol sachets are all there 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.

Pharmacist recommended products

Any reason to avoid it?

You should take lactulose with caution if you are diabetic, as this is a form of sugar and may affect your sugar levels at high doses, or if you have very 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 in a similar way but doesn’t disrupt sugar levels.

Lactulose purchased over the counter 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 is you are lactulose-intolerant, and avoid lactulose if you have galactosaemia or any holes or perfusions in the intestines.

Lactulose is suitable for children aged over 1 year, and doses can be adjusted according to response or as otherwise recommended by a pharmacist or doctor.

Are there any side effects?

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

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Dr Roger Henderson
Reviewed by Roger Henderson
Reviewed on 29.04.2024
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