This study is a randomized, controlled, single centre, endoscopist-blinded non-inferiority trial. The purpose of our study is to determine if using a 2-litre mixture in combination with vitamin C is better than using 2 litres of mixture with bisacodyl tablets. Two-litre PegLyte based preparations with an added laxative agent are commonly used for colonoscopies in outpatient settings. If the investigators discover that a 2-litre mixture with either the tablets or the ascorbic acid work better, future patients undergoing colonoscopy will be able to experience fewer side effects and be less troubled by the preparation while still allowing a good view of the colon.

All adults (≥ 19 yrs of age) who are referred to St. Paul's Hospital for outpatient colonoscopy will be included in our study. Exclusion criteria included those with constipation, suspected or known small bowel obstruction, severe inflammatory bowel disease, and any history of colonic resection. 278 consecutive eligible patients will be randomized to one of two bowel preparations through the use of concealed allocation by a scheduling assistant (blinded) in a one-to-one allocation ratio. Bowel preparations included: (i) 2 L of MoviPrep (2 L PEG 3350 electrolyte solution + ascorbic acid) or (ii) Bi-Peglyte (2 L PEG 3350 electrolyte solution and 15mg bisacodyl). Patients in both arms will be instructed to adhere to a clear liquid diet commensing 24 hours prior to scheduled colonoscopy in addition to their remaining bowel preparation.

The investigators will not have access to the randomization envelopes and the randomized bowel preparation will be stored within the medical record that will not be accessible by the endoscopist. The endoscopists can break blinding and access the bowel prep given when medically necessary.

At the time of their procedure check-in, written consent will be confirmed and patients will respond to a brief survey assessing patient tolerance. All colonoscopies will be performed under conscious sedation by an experienced endoscopist. Endoscopists will be blinded to the bowel preparation until the completion of the study. We will use the Boston Bowel Preparation Scale (BBPS) and Ottawa Bowel Preparation Scale (OBPS) to assess efficacy in bowel preparation.

Inclusion Criteria:

• All adults (≥ 19 years of age) who are referred to St. Paul's Hospital for outpatient colonoscopy will be included in our study.

Exclusion Criteria:

• those with constipation,
• suspected or known small bowel obstruction,
• severe inflammatory bowel disease, and
• any history of colonic resection.