Chronic constipation is one of the risk factors of inadequate bowel preparation, which could influence the effect of colonoscopy. The risk factors associated with inadequate bowel preparation in constipated patients remains unclear. Here the investigators investigated the high risk factors which might have influence on bowel preparation quality in a prospective cohort of patients with functional constipation.

Inclusion Criteria:

• 18-90
• Patients undergoing colonoscopy;
• Patients meeting the criteria of chronic constipation of Rome Ⅳ;

Exclusion Criteria:

• history of colorectal surgery;
• known of suspected colonic stricture or obstructing tumour;
• ulcerative colitis;
• Crohn's disease;
• irritable bowel syndrome;
• toxic colitis or megacolon;
• known or suspected bowel obstruction or perforation;
• pregnancy or lactation;
• unable to give informed consent;
• haemodynamically unstable.

patients >=18 years old undergoing colonoscopy