Is it absolutely essential that i drink all of the bowel prep before i have a colonoscopy?

Yes: Yes so that your colon is clean enough. If you choose not to, the endoscopist may not be able to see everything' could potentially miss a lesion, and with an inadequate prep, i usually recommend that i repeat the scope much sooner than if i was comfortable i could see everything well. E.G repeat in 5 yrs instead of 10.

Drink it all or call: The point of the colonoscopy is to allow the endoscopist to evaluate the colon fully. This can't happen if stool remains in the colon. It's not just the chunky stuff: liquid stool coating the colon lining also makes it very hard to see. So if you are going to bother to go for a colonoscopy, give yourself the best chance for a good exam. If you just can't drink the prep, call your doctor for advice.