Lactitol and lactulose are both used to treat constipation, but they differ in their structure and some properties. Lactitol is a synthetic disaccharide made from galactose and sorbitol, while lactulose is a naturally occurring disaccharide made from galactose and fructose. Although they work similarly by drawing water into the intestines, some patients may prefer one over the other due to personal preference or specific medical needs.