Medically Reviewed on 4/13/2022

Generic Name: lactulose

Brand Names: Enulose, Kristalose, Constulose, Generlac

Drug Class:  Laxatives, Osmotic; Ammonium Detoxicants

What is lactulose, and what is it used for?

Lactulose is a synthetic sugar derived from lactose, the sugar found in dairy products. Lactulose is used to relieve constipation and to prevent and treat portal systemic encephalopathy (PSE), a condition in which neurotoxins in the blood accumulate and damage the brain tissue because the liver fails to remove the toxins from the blood. lactulose may be administered orally or rectally.

Lactulose consists of two sugar molecules (disaccharide), one galactose and one fructose. Lactulose is an osmotic laxative that softens the stools by drawing water into the colon. The bacteria in the intestines break lactulose down into lactic and other organic acids, acidifying the colonic contents, and generate gasses such as hydrogen and methane. Both these actions contribute to increase in the colonic water content and promotion of the muscle contractions (peristalsis) that facilitate bowel movement.

Portal systemic encephalopathy is caused when the liver fails to remove ammonia and other neurotoxins from the blood, which get deposited in the brain. PSE results when blood bypasses the purification process in the liver because of an abnormal connection (portosystemic shunt) which can result from liver cirrhosis or from congenital malformation. The acidification of the intestinal contents by lactulose draws the ammonia and other waste products in the blood into the colon, which are then eliminated in the stools.


  • Do not administer to patients who are hypersensitive to lactulose or any of its ingredients
  • Do not administer to patients who are unable to metabolize galactose and have high galactose levels in blood (galactosemia) because lactulose contains galactose
  • Use with caution in patients with diabetes; lactulose contains sugars
  • Do not use lactulose concurrently with other laxatives
  • Electrolyte imbalances may result from chronic use, particularly in patients predisposed to electrolyte imbalances, including infants; infants may also develop dehydration with low sodium levels (hyponatremia); use with caution and monitor periodically
  • There is a theoretical risk of reaction between hydrogen gas accumulation in the colon and electrical spark from electrocautery procedure during proctoscopy or colonoscopy; cleanse the bowels thoroughly with a nonfermentable solution prior to procedure
  • Response to lactulose may be reduced if taken simultaneously with anti-infective agents

What are the side effects of lactulose?

Common side effects of lactulose include:

This is not a complete list of all side effects or adverse reactions that may occur from the use of this drug.

Call your doctor for medical advice about serious side effects or adverse reactions. You may also report side effects or health problems to the FDA at 1-800-FDA-1088.


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What are the dosages of lactulose?

Oral/Rectal Solution

  • 10g/15mL


  • 10g
  • 20g



  • Solution: 15-30 mL (10-20 g) orally once daily; may be increased to 60 mL (40 g) once daily
  • Crystals: 10-20 g orally every day; may increase to 40 g/day

Portal Systemic Encephalopathy


  • 30-45 mL (20-30 g) orally every 6-8 hours, adjusted until 2-3 soft stools/day; if acute, may be given every 1-2 hours until 2-3 soft stools/day


  • 20-30 g (30-45 mL) orally every 1 hour to induce rapid defecation; reduced to 20-30 g every 6-8 hours after defecation achieved; titrated to produce 2-3 soft stools/day
  • 300 mL (200 g) rectally with 700 mL water or normal saline, retained for 30-60 minutes; may be repeated every 4-6 hours; transition to oral treatment before discontinuance of rectal administration



  • 0.7-2 g/kg/day (1-3 mL/kg/day) orally in divided doses; not to exceed 40 g/day (60 mL/day)

Portal Systemic Encephalopathy


  • Infants: 2.5-10 mL/day (1.7-6.67 g/day) orally in divided doses; titrated to produce 2-3 soft stools/day
  • Children and adolescents: 40-90 mL/day (26.7-60 g/day) orally in divided doses; titrated to produce 2-3 soft stools/day


  • Symptoms of lactulose overdose may include abdominal cramps and diarrhea.
  • In case of overdose, discontinue lactulose and seek medical help or contact Poison Control.

What drugs interact with lactulose?

Inform your doctor of all medications you are currently taking, who can advise you on any possible drug interactions. Never begin taking, suddenly discontinue, or change the dosage of any medication without your doctor’s recommendation.

  • Lactulose has no known severe interactions with other drugs.
  • Lactulose has no known serious interactions with other drugs.
  • Moderate interactions of lactulose include:
  • Lactulose has no known mild interactions with other drugs.

The drug interactions listed above are not all of the possible interactions or adverse effects. For more information on drug interactions, visit the RxList Drug Interaction Checker.

It is important to always tell your doctor, pharmacist, or health care provider of all prescription and over-the-counter medications you use, as well as the dosage for each, and keep a list of the information. Check with your doctor or health care provider if you have any questions about the medication.

Pregnancy and breastfeeding

  • Lactulose use during pregnancy may be acceptable when diet and lifestyle modifications are ineffective in relieving constipation.
  • It is not known if lactulose is present in breast milk; use with caution in nursing mothers.

What else should I know about lactulose?

  • Take lactulose exactly as prescribed
  • Store out of reach of children


Lactulose is a synthetic sugar derived from lactose, the sugar found in dairy products. Lactulose is used to relieve constipation and to prevent and treat portal systemic encephalopathy (PSE). Common side effects of lactulose include abdominal distention, abdominal cramping, excessive bowel activity, diarrhea, gas (flatulence), belching, nausea, vomiting, dehydration, high sodium levels (hypernatremia), and low potassium levels (hypokalemia). Use with caution in patients with diabetes (lactulose contains sugars). Use with caution in nursing mothers and during pregnancy.

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Medically Reviewed on 4/13/2022