Bowel preparation affects the quality of colonoscopy. Reaching the optimal preparation has been a challenge for years. Polyethylene glycol (PEG) is the sole FDA-approved substance for this purpose. However, patients find it unpleasant and often complain about its adverse effects. In this study, we aimed to reduce these complaints by lowering the amount of PEG and adding senna which is an herbal stimulant laxative.