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About lactulose

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.

Key facts

  • Lactulose relieves constipation by drawing water into your bowel to make poo softer.
  • The most common side effects are diarrhoea, bloating and wind. These are usually mild and do not last long.
  • Lactulose takes at least 2 days to work. Talk to your doctor if your constipation has not improved after 4 or 5 days.
  • If you find the taste of lactulose too sweet, you can dilute it with fruit juice or water.

Page last reviewed: 4 March 2022
Next review due: 4 March 2025