Abstract
OBJECTIVETo assess the interplay between metformin treatment and thyroid function in type 2 diabetic patients.RESEARCH DESIGN AND METHODSThe acute and long-term effects of metformin on thyroid axis hormones were assessed in diabetic patients with primary hypothyroidism who were either untreated or treated with levothyroxine (L-T4), as well as in diabetic patients with normal thyroid function.RESULTSNo acute changes were found in 11 patients with treated hypothyroidism. After 1 year of metformin administration, a significant thyrotropin (TSH) decrease (P < 0.001) was observed in diabetic subjects with hypothyroidism who were either treated (n = 29; from 2.37 ± 1.17 to 1.41 ± 1.21 mIU/l) or untreated (n = 18; 4.5 ± 0.37 vs. 2.93 ± 1.48) with L-T4, but not in 54 euthyroid subjects. No significant change in free T4 (FT4) was observed in any group.CONCLUSIONSMetformin administration influences TSH without change of FT4 in patients with type 2 diabetes and concomitant hypothyroidism. The need for reevaluation of thyroid function in these patients within 6–12 months after starting metformin is indicated.
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