Get our free Cephulac coupon and be eligible to receive a discount. You can reduce your Cephulac cost by up to 75% with our free Cephulac discount card. Bring it to a participating pharmacy near you to save on your prescription medication.Lactulose is 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. Lactulose is used to treat chronic constipation. Lactulose may also be used for other purposes not listed in this medication guide.