Background: the majority of individuals in sweden with type 2 diabetes have theirsole health care provider in primary health care. Metformin treatment often causesgastrointestinal side-effects. Our aim was to construct and validate a questionnaireassessing gastrointestinal symptoms before and after starting metformin treatment fortype 2 diabetes.Methods: in the interaction Between Metformin and Microbiota (MeMO) study, 54participants rated six gastrointestinal symptoms at baseline and after 2 months ofmetformin treatment in a questionnaire (measured change, i.e. the difference betweenassessments at these two time points), as well as direct assessment of perceived changein symptoms after 2 months in a separate validation questionnaire (reported change, i.e.how participants themselves have perceived the change between the same two timepoints). spearman’s ρ was calculated and reported with its 95% ci.Results: the agreement between reported and measured change of symptoms,measured as spearman’s ρ, was above 0.4 for 4 out of 6 symptoms (poor appetite 0.60[95% ci 0.39–0.75], loose stool or diarrhea 0.58 [95% ci 0.37–0.74], flatulence 0.45 [95%ci 0.21–0.64], and abdominal pain 0.45 [95% ci 0.20–0.65]). the agreement was lowerfor nausea and vomiting, although these were numerically above 75% in agreement,likely due to few symptomatic participants overall.Conclusion: For common side-effect symptoms associated with metformin treatment,our study shows that symptom change measured as the difference between assessmentsat two different time-points was in overall agreement, validating the usability of theconstructed questionnaire for metformin side-effects.