Jin 2006.

Study characteristics
Methods	Randomised controlled trial Location of the trial: quote: Beijing, China Method of randomisation: quote: "Randomly divided into 4 groups" Method of allocation concealment: not stated Source of funding: Not stated
Participants	Inclusion criteria: women with PCOS according to Rotterdam criteria, normal liver and kidney function, no treatment provided 3 months prior to the study. Exclusion criteria: congenital adrenal hyperplasia (CAH); Cushing's syndrome; hyperprolactinaemia; thyroid disease; hormone‐secreting tumours. Number of women randomised: 24 MET: 15 OCP: 10 Number of women analysed: 24 MET: 15 OCP: 10 Number of withdrawal and reasons: 0 Summary characteristics: PCOS Age (years): MET mean (+SD): 23.3 (6.53) OCP mean (+SD): 23 (6.11)
Interventions	Treatment: MET oral, 500 mg/time, three times a day Control: OCP (Ethynil Estradiol 35 mcg/ Cyproterone acetate 25 mg) start on day 5 of menstrual cycle, continued for 21 days; one pill a day Duration: 3 months Co‐intervention(s): none
Outcomes	Primary outcomes: Hirsutism (assessed clinically and subjectively) Secondary outcomes: Improved menstrual pattern (i.e. an initiation of menses or significant shortening of cycles or intermenstrual days) Acne (assessed clinically and subjectively) BMI (kg/m2) Serum total testosterone (n mol/L) Fasting insulin (mIU/L)
Subjective outcomes	(a) Clinical parameters Hirsutism (assessed clinically and subjectively) Acne (assessed clinically and subjectively)
Objective outcomes	(a) Clinical parameters Improved menstrual pattern (i.e. an initiation of menses or significant shortening of cycles or intermenstrual days) BMI (kg/m2) (b) Hormonal parameters Serum total testosterone (n mol/L) (c) Metabolic parameters Fasting insulin (mIU/L)
Notes	Power calculation: no
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "Randomly divided into 4 groups" Insufficient information about the sequence generation process available to permit a judgement of 'low risk' or 'high risk'
Allocation concealment (selection bias)	Unclear risk	Method of allocation concealment not stated. Insufficient information available to permit a judgement of 'low risk' or 'high risk'
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Insufficient information available to permit a judgement of ‘low risk’ or ‘high risk’. Blinding not stated.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Insufficient information available to permit a judgement of ‘low risk’ or ‘high risk’. Blinding not stated.
Incomplete outcome data (attrition bias) All outcomes	Low risk	No missing outcome data.
Selective reporting (reporting bias)	High risk	Hirsutism and acne described with score in the methods (Ferriman‐Gallwey score; acne score) but reported in the results as number of patients who had an improvement. BMI not reported in the results. One or more primary outcomes have been reported using measurements, analysis methods or subset of the data that were not prespecified.
Other bias	High risk	Baselin imbalance.