A Cochrane review [Abstract] 1 included 44 trials involving a total of 2253 women. Metformin was less effective in improving hirsutism compared to combined oral contraceptives (COC) in the subgroup BMI 25 kg/m² to 30 kg/m² (MD 1.92, 95% CI 1.21 to 2.64, 5 RCTs, n = 254), but there were no clear difference in the subgroup BMI under 25. Either metformin alone or COC alone may be less effective in improving hirsutism compared to metformin combined with COC. Metformin resulted in a higher incidence of gastrointestinal and a lower incidence of non-gastrointestinal severe adverse effects requiring stopping of medication.
Comment: The quality of evidence is downgraded by study quality (lack of blinding, inadequate intention-to-treat) and by imprecise results (few patients and wide confidence intervals).
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