I have ulcerative colitis, IBS-D and severe GERD and have had approx. 15 colonoscopies in the past ten years, endoscopy about every other year and, for me, have never had any long term problems from the prep. I hate to add something to your current concerns, but I believe the sigmoidoscopy is a worthless procedure and most MD's (let's say HMOs) do it first b/c it's a much cheaper procedure, but, if the sigmoid doesn't reveal anything then--if your MD is competent--will suggest doing the full colonoscopy--which they just should have done in the first place. A friend of mine suffered an extra six months b/c her GI MD did a sigmoid first, didn't see anything and said she must just have colitis "or something" but it was colon cancer and wasn't detected b/c the sigmoid, as you may not know, does not check the entire colon. I always advise friends to demand the colonoscopy in the first place, the MD will resist, but ask how, if there is cancer in the upper colon area, will the sigmoid detect it if it doesn't go all the way up? It seems to work.