About 30% of patients were reported to suffer inadequate bowel preparation. So, it is desirable to prescribe personalized regimen according to patient's personal characteristics.

Colonoscopy is currently the main approach for detecting mucosal abnormalities in the whole colon. Inadequate bowel preparation is the predominant threaten to the efficacy of colonoscopy.Unfortunately, about 30% of patients were reported to suffer inadequate bowel preparation. In order to improve adequate bowel preparation rate, it is desirable to prescribe personalized regimen according to patient characteristics. We intend to improve adequate bowel preparation rate by deploying tailored bowel preparation strategy. There are many predictive factors of inadequate bowel preparation such as obesity, constipation, abdominal surgery and so on. By recognizing these risk factors of the patients , we can prescribe the patients with higher dose of bowel cleansing regimen to improve bowel preparation quality.

Inclusion Criteria:

• patients aged 18 or older
• patients undergoing colonoscopy

Exclusion Criteria:

• patients with a history of colorectal surgery
• patients with severe colonic stricture or obstructing tumor
• patients with dysphagia
• patients with compromised swallowing reflex or mental status
• patients with significant gastroparesis or gastric outlet obstruction
• patients with known or suspected bowel obstruction or perforation
• patients with severe chronic renal failure (creatinine clearance<30 ml/min)
• patients with severe chronic renal failure (creatinine clearance<30 ml/min)
• patients with uncontrolled hypertension (systolic blood pressure>170 mm Hg, diastolic blood pressure>100 mm Hg)
• patients with inflammatory bowel disease or megacolon
• patients with dehydration
• patients with dehydration
• patients with pregnancy or lactation
• patients hemodynamically unstable
• patients unable to give informed consent

The individual participant data of this trial will be shared when necessary