Lactulose is a non-absorbable sugar used in the treatment of constipation and hepatic encephalopathy. It is administered orally for constipation, and either orally or rectally for hepatic encephalopathy. It generally begins working after 8–12 hours, but may take up to 2 days to improve constipation.
Common side effects include abdominal bloating and cramps. A potential exists for electrolyte problems as a result of the diarrhea it produces. No evidence of harm to the fetus has been found when used during pregnancy. It is generally regarded as safe during breastfeeding. It is classified as an osmotic laxative.
Lactulose was first made in 1929, and has been used medically since the 1950s. Lactulose is made from the milk sugar lactose, which is composed of two simple sugars, galactose and glucose. It is on the World Health Organization's List of Essential Medicines. It is available as a generic medication. In 2021, it was the 265th most commonly prescribed medication in the United States, with more than 1million prescriptions.