Colorectal cancer, the third most common cancer in U.S. adults, can be detected early through colonoscopy. Thorough bowel preparation facilitates successful colonoscopy. Effectiveness, tolerability, and costs of 3 bowel preparations were compared in patients undergoing outpatient screening colonoscopy. In this prospective, randomized, single-blind study, comparing three preparation protocols, 209 of 276 consented subjects completed (Protocol [N = 67] = HalfLytely© 1 L × 2 doses and bisacodyl 5 mg delayed release tablets × 2 tablets; Protocol 2 [N = 74] = MiraLAX® 5 tablespoons × 2 doses and bisacodyl 5 mg tablets × 2 tablets; and Protocol 3 [N = 68] = MoviPrep 1 L × 2 doses). Patients completed symptom diaries and a gastroenterologist rated effectiveness. Most subjects were White females, aged 59 years (mean). Protocol 1 was the most effective regimen, but Protocol 2 was the most tolerable and cost-effective. While the three bowel protocol differences were not statistically significant for all outcomes measured, there were clinically meaningful differences. As Protocol 1 was most effective, HalfLytely© and bisacodyl is recommended for patients prior to colonoscopy. For patients who cannot tolerate HalfLytely© or MoviPrep, or with financial concerns, Protocol 2 (MiraLAX® & bisacodyl) is alternatively recommended.