Lactulose is contraindicated in case of galactosemia, as most preparations contain the monosaccharide galactose due to its synthesis process.

[14][15] Lactulose may be used to counter the constipating effects of opioids, and in the symptomatic treatment of hemorrhoids as a stool softener.

[medical citation needed] Lactulose is commonly prescribed for children who develop fear of their bowel movements and are withholders.

This is because lactulose, when dosed in the proper amount, causes a bowel movement that is impossible to retain for very long.

[medical citation needed] Lactulose is useful in treating hyperammonemia (high blood ammonia), which can lead to hepatic encephalopathy.

An alternate explanation for differences in results is the variance in small bowel transit time among tested subjects.

In sensitive individuals, such as the elderly or people with reduced kidney function, excess lactulose dosage can result in dehydration and electrolyte disturbances such as low magnesium levels.

Although lactulose is less likely to cause dental caries than sucrose, as a sugar, a potential for this exists, which is relevant when taken by people with a high susceptibility to this condition.

[citation needed] Lactulose is not absorbed in the small intestine nor broken down by human enzymes, thus stays in the digestive bolus through most of its course, causing retention of water through osmosis leading to softer, easier-to-pass stool.

[25] Moreover, research showed improved cognitive functions and health-related quality of life in people with cirrhosis with minimal hepatic encephalopathy treated with lactulose.

[26] Lactulose is a disaccharide formed from one molecule each of the simple sugars (monosaccharides) fructose and galactose.