Wiegand 2010.

Methods	Parallel randomised controlled trial, randomisation ratio 1:1, superiority design
Participants	Inclusion criteria: obese aged 10 to 17 years HOMA IR > 3 or > 95th percentile according to Allard et al nondiabetic normal liver and kidney function already were enrolled in the trial Exclusion criteria: pre‐existing diabetes pregnancy liver enzymes > 1.5 times the upper limit of normal or elevated creatinine > 1.5 mg/dL severe chronic or mental illness Diagnostic criteria: obesity (not defined)
Interventions	Intervention: metformin + multiprofessional lifestyle intervention Comparator: placebo + multiprofessional lifestyle intervention Number of trial centres: 2 Treatment before trial: 6‐month multiprofessional lifestyle intervention Titration period: no
Outcomes	Outcomes reported in abstract of publication: BMI, HOMA‐IR, fasting insulin, insulin sensitivity index, metabolic syndrome
Study details	Run‐in period: no Trial terminated early: no
Publication details	Language of publication: English Commercial and noncommercial funding Publication status: peer‐reviewed journal
Stated aim for study	Quote from publication: "To study whether metformin reduces obesity, homeostasis model assessment for insulin resistance index (HOMA‐IR), and the metabolic syndrome (MtS) in obese European adolescents in addition to previous unsuccessful lifestyle intervention"
Notes	‐
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Comment: no description of the randomisation process
Allocation concealment (selection bias)	Unclear risk	Comment: unclear if allocation was concealed
Blinding of participants and personnel (performance bias) Objective outcomes	Unclear risk	Quote: "we performed a double‐blind, randomized controlled clinical trial" Comment: unclear who was blinded
Blinding of participants and personnel (performance bias) Subjective outcomes	Unclear risk	Quote: "we performed a double‐blind, randomized controlled clinical trial" Comment: unclear who was blinded
Blinding of outcome assessment (detection bias) Objective outcomes	Unclear risk	Quote: "we performed a double‐blind, randomized controlled clinical trial" Comment: unclear who was blinded
Blinding of outcome assessment (detection bias) Subjective outcomes	Unclear risk	Quote: "we performed a double‐blind, randomized controlled clinical trial" Comment: unclear who was blinded
Incomplete outcome data (attrition bias) Objective outcomes	Unclear risk	Comment: no imputation method was used to replace missing data; however, dropout was fairly low
Incomplete outcome data (attrition bias) Subjective outcomes	Unclear risk	Comment: no imputation method was used to replace missing data; however, dropout was fairly low
Selective reporting (reporting bias)	Unclear risk	Comment: unable to find the clinical trial entry; hence, it is unclear whether selective reporting occurred
Other bias	High risk	Quote: "The study was supported in part by BMBF Research grant 01 GS 0825 and by MERCK SANTE S.A.S, Lyon, France (10’000,‐ Euro)" Comment: trial was partly funded by a pharmaceutical company. The authors do not declare their involvement in the design, analysis and interpretation of the results