The purpose of this study is to observe the difference in bowel preparation quality between compound sodium picosulfate#CSP combined with lactulose and polyethylene glycol electrolyte#PEG combined with lactulose in high-risk population.

The quality of bowel preparation is crucial for colonoscopy. Some high-risk factors for inadequate bowel preparation have been identified , including age >70, previous colon surgery, constipation, diabetes, Parkinson's disease, history of stroke or spinal cord injury, prior history of inadequate bowel preparation, body mass index (BMI) >25, use of tricyclic antidepressant or narcotics. Patients were considered as high risk if they have any of the above factors.This is a single-center ,endoscopist-blinded study to compare the efficacy of CSP combined with lactulose and PEG combined with lactulose in bowel preparation. In colonoscopy procedures, endoscopists who were blinded to the intervention evaluated the overall quality of colonoscopy cleaning according to the Boston Bowel Preparation Scale. Patients' tolerance, defecation, adverse events and adenoma detection rate (ADR) were also evaluated.

Inclusion Criteria:Adults undergoing colonoscopy who have at least one risk factor: age>70, previous colon surgery, constipation, diabetes, Parkinson's disease, history of stroke or spinal cord injury, prior history of inadequate bowel preparation, body mass index (BMI) >25, use of tricyclic antidepressant or narcotics.

Exclusion Criteria:

1. presence of any contraindications for colonoscopy (gastrointestinal obstruction or perforation,severe acute inflammatory bowel disease,toxic megacolon,severe heart failure,unable to swallow,severe heart failure,etc);
2. Patients with galactosemia;
3. hypersensitivity to any of the ingredients;
4. Pregnancy or lactation;
5. Use of lactulose,prokinetic agents or purgatives within 7 days;
6. Unwilling to sign informed consent.