Background and AimThe addition of a laxative prior to a standard bowel preparation (BP) has shown variable results in efficacy, safety, and tolerability of the BP. This study compared the efficacy and tolerability of a macrogol‐augmented BP (M‐BP) with standard BP for routine colonoscopy in unselected patients.MethodsAdults undergoing outpatient colonoscopy were randomized to either M‐BP (one sachet of macrogol‐based osmotic laxative (MBOL) twice daily for eight doses prior to standard preparation) or BP (split‐dose of polyethylene glycol and sodium picosulfate). Bowel cleansing was assessed using the Ottawa BP scale. Risk factors for poor BP, patient satisfaction, and tolerance were recorded.ResultsThis randomized trial was stopped due to futility after 14 months; at that point, 92 subjects were randomized to the study arm and 102 to the control arm. M‐BP had a success rate of 71.7% (95% CI: 58.5–82.7%), while the BP had a success rate of 67.7% (95% CI: 54.9–78.8%), with a Pearson χ2 test P‐value of 0.639, which exceeded the cut‐off for futility (0.313). In subgroup analyses, there were statistically significant decreases in the rates of successful BP in patients taking regular opioids and regular laxatives. Both preparations were well tolerated, with no difference between groups (BP – 5.3% and M‐BP – 6.6% P = 0.66).ConclusionThe addition of MBOL prior to a standard BP in unselected subjects does not significantly improve bowel cleanliness at routine colonoscopy. The role of this laxative in patients at high risk of poor preparation warrants further investigation.