Colorectal cancer is the first neoplasm most commonly diagnosed in both sexes and the second leading cause of cancer death in Spain. Colorectal cancer screening Program in Barcelona was implanted in 2009 and approximately 1,500 colorectal cancer screening colonoscopies are performed annually at Hospital Clínic de Barcelona. Adequate colon preparation (anterograde cleansing with laxatives) improves polyp detection, decreases examination time, and complications. There are both low and high volume intestinal regimens with polyethylene glycol (PEG) as the main active ingredient or without it.

Hypothesis: Two low volumen regimens, 1L PEG plus ascorbate and magnesium citrate plus picosulphate, at starting doses have the same Adenoma Detection Rate as cleansing solutions in preparation for screening colonoscopy.

The primary objective of the study is to compare the clinical efficacy (by comparing the adenoma detection rate) of 1L PEG plus ascorbate versus magnesium citrate plus picosulphate in subjects undergoing colonoscopy in a colorectal cancer screening programme. We also will compare the Lesion Detection Rate, the quality of colon cleansing (Boston classification) overall and by segments, the tolerability and satisfaction and the rate of adverse effects experienced with intake of these products.

Methodology: A comparative, parallel, randomized, single-centre, low-intervention clinical trial to be conducted at the CCR screening unit of Hospital Clínic de Barcelona that will include 1,002 participants.

Subjects will complete a Tolerability and Satisfaction Questionnaire after completing the bowel preparation. Findings (polyps, CRC, or other lesions) and quality of bowel cleansing will be collected from the colonoscopy report.

Inclusion Criteria:

• Men and women aged 50 to 69 years who have participated in the early detection programme for colon and rectal cancer (PDPCCR) in Barcelona, who have obtained a positive result in the faecal occult blood test (≥20 μg Hb/g faeces) and who are scheduled for a screening colonoscopy at Hospital Clínic de Barcelona.

Exclusion Criteria:

• People who do not agree to participate in the study.
• People with known severe renal failure (grade IV or V) and grade III and IV heart failure according to the New York Heart Association (NYHA) Scale of Functional Assessment of Heart Failure
• Individuals who have undergone a colonoscopy in the past year.
• Subjects meeting the Rome IV Criteria for the diagnosis of functional constipation
• Subjects with mental disabilities or with a severe mental disorder (schizophrenia and other psychotic disorders, recurrent severe major depressive disorders, severe obsessive-compulsive disorder, severe personality disorders and bipolar disorders).
• Individuals who do not understand Catalan or Spanish verbally and in writing.
• Individuals with partial or total colon resection.
• Individuals with a personal history of CRC or colorectal disease amenable to specific follow-up (ulcerative colitis, Crohn's disease, or colorectal adenomas).
• Individuals with terminal illness or severe illness/disability that contraindicates further study of the colon.
• People with gastrointestinal disorders that contraindicate the use of the study products (gastric emptying disorders, perforation or gastrointestinal obstruction, ileus, toxic megacolon).
• People with congestive heart failure
• Hypermagnesemia
• Rhabdomyolysis
• Phenylketourine
• Glucose-6-phosphate dehydrogenase deficiency
• People with hypersensitivity to the active ingredients of excipients
• People with severe renal impairment