Objective: To assess the effect of metformin administration on thyroid function in overweight women with polycystic ovarian syndrome (PCOS).
Methods: Twenty-seven overweight women with PCOS and hypothyroidism were selected. Fifteen patients (group I) were treated with metformin 1500 mg/day for 6 months and 12 patients (group II) with placebo. Serum thyrotropin (TSH), free T3 and free T4 were measured at baseline and 6 months after the beginning of the study.
Results: A significant decrease (p<0.001) in TSH levels was observed in group I but not in group II subjects after 6 months of metformin treatment. No significant change in free T3 and free T4 was observed throughout the study in any group.
Conclusion: In obese PCOS patients with primary hypothyroidism, metformin results in a significant fall and sometimes normalisation of TSH, without causing any reciprocal changes in other thyroid function parameters.