Lactulose (Standard) is the analytical standard of Lactulose. This product is intended for research and analytical applications. Lactulose (4-O-beta-D-Galactopyranosyl-D-fructose) is a poorly absorbed sugar that can be used to study constipation and hepatic encephalopathy. The drug generally begins to take effect 8 to 12 hours after administration, but it may take two days to improve constipation.