Body Mass Index (BMI) Dependent Effect of Glucagon Like Peptide 1 Receptor Agonist (GLP-1RA) Therapy on Bowel Preparation Quality

INTRODUCTION: Glucagon-like peptide-1 receptor agonist (GLP-1RA) therapy has been associated with inadequate bowel preparation during colonoscopy, but the role of baseline BMI remains unclear. We aim to assess whether baseline BMI modifies the association between GLP-1RA use and bowel preparation adequacy and lesion detection, hypothesizing a BMI-dependent effect modification. METHODS: We conducted a retrospective cohort study of 51,268 patients (46,883 controls, 4,385 GLP-1RA treated) undergoing colonoscopy. Patients were grouped by BMI category from normal or overweight to Class III obesity. Multivariable logistic regression models incorporating treatment × BMI interaction terms were used to formally test for effect modification. Primary outcomes were inadequate bowel preparation, adenoma detection, and sessile serrated polyp detection. Analysis was adjusted for age, sex, race, diabetes, and gastrointestinal medications. RESULTS: GLP-1RA use demonstrated significant BMI-dependent effect modification for inadequate bowel preparation (global likelihood ratio test p=0.001). In normal or overweight patients, GLP-1RA therapy was associated with increased odds of inadequate bowel preparation (OR 1.66; 95% CI 1.37-2.02; p<0.001). This effect progressively attenuated with increasing BMI and was negligible in Class III obesity. GLP-1RA therapy did not demonstrate an additional adverse impact on adenoma or sessile serrated polyp detection rates compared to patients in similar BMI categories not receiving the therapy. CONCLUSIONS: GLP-1RA therapy increased inadequate bowel preparation risk primarily in normal and overweight patients, with minimal effect in severe obesity. BMI stratification may inform personalized colonoscopy preparation strategies in GLP-1RA treated patients.