Mechanism of Action of Lactulose

Primary Mechanisms

Lactulose works as an osmotic laxative by drawing water into the intestine to hydrate and soften stool, and in hepatic encephalopathy, it acidifies colonic contents through bacterial fermentation, trapping ammonia as the ammonium ion and preventing its absorption, according to the American Gastroenterological Association 1
Once in the colon, lactulose draws water into the intestinal lumen, creating an osmotic gradient that hydrates and softens stool, as recommended by the American Gastroenterological Association 1, 2

Gastrointestinal side effects, such as bloating, flatulence, and abdominal cramps, occur in approximately 20% of patients due to the fermentation process producing gas, as reported by the European Society of Gastroenterology 3, 4
Starting at lower doses and titrating upward minimizes these dose-dependent side effects, according to the European Society of Gastroenterology 3, 4
Excessive dosing can lead to diarrhea with complications including hypokalemia and hypernatremia from fluid and electrolyte losses, as warned by the European Society of Gastroenterology 4