Colonoscopy is the best method to detect colorectal cancer and colonic polyps. Studies showed that adenoma detection rate positive correlation with good bowel preparation which makes bowel preparation an important issue. Hence, investigators conduct a clinical trial about adding another laxative agent to morning single dose low-volume PEG. To see if this new regimen could have non-inferior efficacy and lower life/sleep impact compared with standard regimen.

Colorectal cancer incidence rate has increased in recently years, and colorectal cancer has come to the top of cancer incidence ranking of Taiwan. Colonoscopy is the best method to detect colorectal cancer and colonic polyps. Studies showed that adenoma detection rate positive correlation with good bowel preparation. That makes bowel preparation an important issue. Polyethylene Glycol (PEG) is widely used for bowel preparation for it efficacy and safety. However, there are many different adjunctive, dose, timing of administration in PEG preparation. Some may decrease patient tolerability due to large fluid volume, and some may influence patient's life and sleep quality when performing bowel preparation. Here, investigators conduct a clinical trial about adding another laxative agent to morning single dose low-volume PEG. To see if this new regimen could have non-inferior efficacy and lower life/sleep impact compared with standard regimen.

Inclusion Criteria:

• Age between 20-70 years.
• Out-patient department ambulatory patient.
• Patients who have indications to receive colonoscopy.

Exclusion Criteria:

• Age is under 20 or over 70
• Have severe renal impairment (hemodialysis or eGFR<30).
• Have severe congestive heart failure (NYHAⅢorⅣ).
• Pregnant or lactating, or women is under oral contraceptive.
• Have history of bowel obstruction or resection, known or suspected gastroparesis acute gastric/intestinal ulcer, toxic colitis or megacolon
• Be allergic to polyethylene glycol (PEG) or bisacodyl.
• Have severe constipation ( ≤ 1 bowel movement per week).
• Patient who has Phenylketonuria.
• Refuse to sign consent to the study.