Rialac Laxative Liquid contains Lactulose which is a colonic acidifier and a type of sugar. It is broken down in the large intestine into mild acids that draw water into the colon, which helps soften the stools. Before taking Rialac, speak to your doctor if you have diabetes or if you need to have any type of intestinal test using a scope (such as a colonoscopy). It may take up to 48 hours before you have a bowel movement after taking this medicine.