TSH-Lowering Effect of Metformin in Type 2 Diabetic Patients

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.

Thyreotropin levels in diabetic patients on metformin treatment

“…The results of the present retrospective study indicate that the TSH-lowering effect of metformin, previously observed in hypothyroid subjects (13), also occurs in euthyroid diabetic patients with basal TSH in the uppernormal range. This effect of metformin appears to occur independently of the presence of AbTPO.…”

“…We also reported a significant reduction of serum TSH levels in diabetic patients with primary untreated hypothyroidism (13). More recently, a decrease in serum TSH was also observed in hypothyroid women being treated with metformin for a coexistent polycystic ovarian syndrome (14,15).…”

“…This observation was confirmed by Isidro et al (12). In a previous study, we showed that treatment with metformin is associated with a significant reduction in the serum levels of TSH in diabetic patients with primary hypothyroidism both untreated and on L-T 4 replacement therapy (13). Evidence for this TSHlowering effect of metformin was recently extended to overweight women with polycystic ovarian syndrome and hypothyroidism (14,15).…”

Metformin inhibits goitrogenous effects of type 2 diabetes

“…While three studies in patients with hypothyroidism and/or levothyroxine treatment showed a reduction of serum TSH levels under metformin treatment (9,10,11), a retrospective study demonstrated significantly higher serum TSH levels in euthyroid patients with T2DM treated with metformin compared with those treated with other diabetic agents (12). However, in that study, metformin use was not associated with serum TSH levels after adjustment for several potential confounding factors of which goiter was the only significant one (12).…”

Subclinical Hypothyroidism in Pregnancy - A Case Series

“…Many other literatures have also documented an association of thyroid abnormalities, notably overt and subclinical hypothyroidism as well as autoimmune thyroiditis with GDM [56][57][58][59][60] . This correlation has been substantiated by depiction of an inverse association between Metforfin and TSH level 61,62,63 . Hence, screening for thyroid dysfunction in diabetes patients, ät-risk" patients for GDM, with anti-TPO antibody positivity, or with TSH concentrations in the upper limits of normal range has been advised by many studies.…”