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Chronulac Side Effects

Generic name: lactulose

Medically reviewed by Last updated on Nov 23, 2023.

Note: This document contains side effect information about lactulose. Some dosage forms listed on this page may not apply to the brand name Chronulac.

Applies to lactulose: oral powder for solution, oral solution, oral syrup.

Serious side effects of Chronulac

Along with its needed effects, lactulose (the active ingredient contained in Chronulac) may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking lactulose:

Incidence not known

Other side effects of Chronulac

Some side effects of lactulose may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects.

Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

Incidence not known

For Healthcare Professionals

Applies to lactulose: compounding solution, oral powder for reconstitution, oral solution, oral syrup, oral and rectal liquid.


Gastrointestinal side effects have included abdominal cramps, gaseous distention, flatulence, belching, bowel distention, cramping, nausea and vomiting, and with excessive doses, diarrhea. Colonic dilatation has been reported in elderly patients. Rare cases of pneumatosis cystoides intestinalis have been reported.[Ref]

Diarrhea is an indication of overdose. Severe diarrhea may lead to hypovolemia, hypokalemia, and hypernatremia, especially in elderly or acutely ill patients. If diarrhea develops, the dosage should be reduced.

Pneumatosis cystoides intestinalis may occur with lactulose therapy as a result of increased intracolonic pressure caused by ammonia sequestration in the bowel, and particularly when there is a concomitant breach of intestinal mucosal integrity.[Ref]


Metabolic side effects have included hypernatremia, hypokalemia and hyperchloremic metabolic acidosis. An isolated case of severe and intractable lactic acidosis has been reported.[Ref]

Fluid and electrolyte disturbances, including severe hypokalemia, hypernatremia and hyperchloremic metabolic acidosis, typically occur as a result of severe diarrhea and subsequent fluid loss. A case of fatal lactulose-induced lactic acidosis in the absence of diarrhea has also been reported. Elderly and/or acutely ill patients may be at increased risk for adverse metabolic effects with lactulose.[Ref]

Frequently asked questions


1. Kot TV, Pettit-Young NA (1992) "Lactulose in the management of constipation: a current review." Ann Pharmacother, 26, p. 1277-82

2. Avery GS, Davies EF, Brogden RN (1972) "Lactulose: a review of its therapeutic and pharmacological properties with particular reference to ammonia metabolism and its mode of action of portal systemic encephalopathy." Drugs, 4, p. 7-48

3. (2002) "Product Information. Chronulac (lactulose)." Hoechst Marion Roussel

4. (2002) "Product Information. Cephulac (lactulose)." Hoechst Marion Roussel

5. Janssen DA, Kalayoglu M, Sollinger HW (1987) "Pneumatosis cystoides intestinalis following lactulose and steroid treatment in a liver transplant patient with an intermittently enlarged scrotum." Transplant Proc, 19, p. 2949-52

6. (2001) "Product Information. Duphalac (lactulose)." Solvay Pharmaceuticals Inc

7. Kaupke C, Sprague T, Gitnick GL (1977) "Hypernatremia after the administration of lactulose ." Ann Intern Med, 86, p. 745-6

8. Mann NS, Russman HB, Mann SK, Tsai MF (1985) "Lactulose and severe lactic acidosis ." Ann Intern Med, 103, p. 637

9. Nelson DC, McGrew WR, Jr Hoyumpa AM, Jr (1983) "Hypernatremia and lactulose therapy." JAMA, 249, p. 1295-8

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.