Subclinical Hyperthyroidism Enhances Gonadotropin‐Lowering Effects of Metformin in Postmenopausal Women

in response to metformin treatment. Although metformin decreased HOMA1-IR in both groups, this effect was stronger in women with hyperthyroidism than with normal thyroid function (-50 ± 20% vs -30 ± 15%). Similar relationships were observed for FSH (-43 ± 21% vs -21 ± 12%). Only in hyperthyroid women did the drug reduce LH concentration (by 35 ± 17%). Metformin did not affect circulating levels of TSH, total and free thyroxine, total and free triiodothyronine, estradiol, prolactin, ACTH, and IGF-1. The obtained results indicate that hyperthyroidism enhances the gonadotropin-lowering effects of metformin, as well as the fact that this agent has a neutral effect on the hypothalamic-pituitary-thyroid axis in case of its overactivity.