Lactulose is a synthetic sugar that is used as a laxative to treat constipation. It works by drawing water into the bowel, which softens and loosens the stool. Lactulose is also used to treat hepatic encephalopathy, a condition that occurs when the liver is not working properly and results in a buildup of toxins in the blood that affect brain function. In this case, lactulose helps to lower the levels of these toxins in the blood by promoting their elimination through the stool. Lactulose is available in oral solution or syrup form and is usually taken once or twice a day, with or without food.