The efficacy and safety of a hypertonic polyethylene glycol - electrolyte lavage solution (PEG-ELS) for patients with constipated patients or regularly user of a laxative: a randomized study

INTERVENTION: A hypertonic PEG‐ELS is administrated for colonoscopy bowel preparation. A conventional PEG‐ELS is administrated for colonoscopy bowel preparation. CONDITION: Patients with chronic constipation, functional constipation or regularly use of a laxative PRIMARY OUTCOME: The rate of poor colon preparation(Ottawa bowel preparation scale>2) and rate of the patients who needed the enema . INCLUSION CRITERIA: (1)Patients with chronic constipation or functional constipation. (2) 20years or older and up to 80 years old. (3) Patients judged to resect polyp in total colonoscopy within the past two years, and undergoing polypectomy. (4) )Written informed consent obtained.