Prado 2012.

Methods	Parallel randomised controlled trial, randomisation ratio 1:1, superiority design
Participants	Inclusion criteria: obese adolescents (BMI > 95th percentile for age and sex) postmenarchal aged 13 to 19 years ≥ 1 risk factor for type 2 diabetes Exclusion criteria: diagnosis of diabetes mellitus type 1 or 2 kidney diseases liver or respiratory alcoholism eating disorders other psychiatric disorders that could diminish adherence to treatment hypersensitivity to metformin pharmacological treatments by metabolic or nutritional impact during the last 3 months pregnancy Diagnostic criteria: obesity defined as BMI > 95th percentile for age and sex. Risk factors for type 2 diabetes include first‐ or second‐degree relative with a history of type 2 diabetes, or alteration in the results of the following examinations within the past 6 months: glycaemia fasting ≥ 100 mg/dL, postload glucose ≥ 140 mg/dL or HOMA > 3.0
Interventions	Intervention: metformin + nutritional guide + exercise programme Comparator: placebo + nutritional guide + exercise programme Number of trial centres: 1 Treatment before trial: none Titration period: no
Outcomes	Outcomes reported in abstract of publication: weight, BMI, metabolic risk profile
Study details	Run‐in period: no Trial terminated early: no
Publication details	Language of publication: Spanish Noncommercial funding Publication status: peer‐reviewed journal
Stated aim for study	Quote from publication: "To analyze the anthropometric and metabolic impact of metformin in obese adolescents at risk for type 2 diabetes"
Notes	‐
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "Recruited adolescents were randomly assigned into two groups (A and B) through a sequence computational randomization" Comment: an appropriate randomisation method was used
Allocation concealment (selection bias)	Low risk	Quote: "An external laboratory was in charge of packing and labelling bottles, keeping content knowledge in confidence until the study ended" Comment: there was allocation concealment
Blinding of participants and personnel (performance bias) Objective outcomes	Low risk	Comment: author confirmed participants and trial personnel were blinded
Blinding of participants and personnel (performance bias) Subjective outcomes	Low risk	Comment: author confirmed participants and trial personnel were blinded
Blinding of outcome assessment (detection bias) Objective outcomes	Unclear risk	Comment: unclear if outcome assessment was blinded and if this would have results in detection bias for the objective outcomes
Blinding of outcome assessment (detection bias) Subjective outcomes	Unclear risk	Comment: unclear if outcome assessment was blinded and if this would have results in detection bias for the subjective outcomes
Incomplete outcome data (attrition bias) Objective outcomes	High risk	Comment: there was no imputation method to replace missing data and dropout rates were fairly high
Incomplete outcome data (attrition bias) Subjective outcomes	High risk	Comment: there was no imputation method to replace missing data and dropout rates were fairly high
Selective reporting (reporting bias)	Unclear risk	Comment: do not give follow‐up data for some outcomes such as blood pressure
Other bias	Unclear risk	Comment: unable to make an assessment on other bias due to lack of information