The effect of
metformin treatment on the hypothalamic-pituitary-thyroid axis is relatively weakly understood. This study included 24 prediabetic patients with
polycystic ovary syndrome and untreated subclinical
hypothyroidism, 12 of whom had already been treated with
bromocriptine (5.0-7.5 mg daily). The included patients received
metformin (2.55 g daily) for 6 months.
Glucose homeostasis
markers, serum prolactin, and thyroid function tests were determined before, after 3 months, and at the end of the treatment. Beyond improving
glucose homeostasis,
metformin administered for 6 months reduced serum levels of
thyrotropin but did not affect serum levels of total and free
thyroid hormones.
Thyrotropin-lowering effect of this agent was stronger in patients not treated with
bromocriptine than in patients receiving this
drug, and weakly correlated with an improvement in
insulin sensitivity. The obtained results indicate that
metformin treatment may have an impact on thyrotrope function in hypothyroid patients, probably by enhancing the effect of
thyroid hormone action in the pituitary.