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Systematic (IUPAC) name
CAS number 4618-18-2
ATC code A06AD11
PubChem 11333
DrugBank APRD01063
Chemical data
Formula C12H22O11 
Mol. mass 342.296 g/mol
Pharmacokinetic data
Bioavailability Poorly absorbed
Metabolism 100% in colon by enteric bacteria
Half life 1.7-2 hours
Excretion Faecal
Therapeutic considerations
Pregnancy cat.


Legal status


Routes Oral

Lactulose is a synthetic sugar used in the treatment of constipation and hepatic encephalopathy, a complication of liver disease. It is a disaccharide (double-sugar) formed from one molecule each of the simple sugars (monosaccharides) fructose and galactose. The commercial syrup used for treatment of constipation is dyed yellow-orange. It is produced commercially by isomerization of lactose.



In the treatment of chronic constipation, its metabolites draw water into the bowel, causing a cathartic effect through osmotic action.

It can be especially useful for negating the constipating effects of opiates and opioids.

It can be also useful for treating children that withhold their bowel movements out of fear.

Lactulose has an overly sweet taste that can be completely masked by mixing it with fruit juice or desserts. It can take 24 to 48 hours to work, but generally produces results within 4 hours if taken on a daily basis. It is best taken at breakfast along with a bowl of bran cereal.

Hepatic encephalopathy

In treating hepatic encephalopathy, lactulose helps "draw out" ammonia (NH3) from the body. The effectiveness of lactulose is somewhat controversial, and whether or not its effects are through ammonia is controversial as well. Lactulose is metabolized in the colon by bacterial flora to short chain fatty acids, acidifying the colonic contents. This favors the formation of the nonabsorbable NH4+ from NH3, trapping NH3 in the colon and effectively reducing plasma NH3 concentrations.

Side effects

Common side effects are abdominal cramping, gas, borborygmus and embarrassing flatulence. Less common side effects are nausea and vomiting. Excessively high dosage can cause explosive and uncontrollable diarrhea. In sensitive individuals, such as the elderly or people with reduced kidney function, excess dosage can result in dehydration and high sodium levels.

Brand names

  • Generlac®
  • Cephulac®
  • Cholac®
  • Constilac®
  • Enulose®
  • Acilac®
  • Heptalac®
  • Actilax®
  • Duphalac®
  • Kristalose®
  • Apo-Lactulose


  • Medline Plus
  • Deglin, J. H., & Vallerand A. H. (2003). Lactulose. In Davis's drug guide for nurses (9th ed.) (pp. 589-590). Philadelphia:F. A. Davis.
  • Actilax / Lactulose Virtual Cancer Centre
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Lactulose". A list of authors is available in Wikipedia.
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