I've had numerous CT Scans. Several before my rectal cancer in 1999 and at least 3 after. Ever since my surgeries this contrast just cleans me out. I joke it's better than the Fleet's Phospho Soda! Now the nurses suggest I consume half the amount recommended and the second dose, in the parking lot, right before reporting for the scan. They said I don't need all of what is suggested on the instruction sheet. I would at least ask if this is your case. As soon as it's over (they also hurry me in), I go straight home. Sure enough, the clean out begins. I also clear my calendar. (I should add that I had a temp ostomy after my colon resection, but I struggle with chronic IBS like symptoms now, so this forum and the IBS have been very helpful to me since my diet is all different now).