Lactulose activates natural mechanisms to restore the microbial balance and function of the colon. It combines different effects, such as supporting colonic bacterial growth, increasing stool volume and activating peristaltics.

Based on this mode of action lactulose is used as an active ingredient of medicinal products to alleviate bowel movements in the treatment of constipation. 
In high dosages lactulose is applied to help lower elevated blood ammonia levels in patients with liver diseases.