Inclusion Criteria:

- elective colonoscopy

- consent to the study

Exclusion Criteria:

- pregnant or lactating women

- age less than 18 years

- significant gastroparesis

- gastric outlet obstruction

- ileus

- known or suspected bowel obstruction or perforation

- phenylketonuria

- glucose-6-phosphate dehydrogenase deficiency

- severe chronic renal failure (creatinine clearance <30 mL/minute)

- severe congestive heart failure (NYHA class III or IV)

- dehydration

- severe acute inflammatory disease

- compromised swallowing reflex or mental status

- uncontrolled hypertension (systolic blood pressure ≥170 mm Hg, diastolic blood
pressure ≥100 mm Hg)

- toxic colitis or megacolon

- previous colonoscopy within the last 5 years

- active Inflammatory bowel disease

- previous colectomy or partial colectomy