Lactulose is a form of sugar that cannot be digested by the human body. In its pharmaceutical preparation, it is used for the treatment of chronic constipation, hepatic encephalopathy and to test for SIBO.
Lactulose can be digested by bacteria in the small intestine and, as a side effect, that process allowed a great deal of water to be retained in the intestines that can loosen stool. This process also draws ammonia out of the blood, which is particularly useful in patients with liver dysfunction.
Lactulose is also used commercially as a sweetener and to promote the growth of digestive bacteria after the use of antibiotics.