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Diabetes Care. 2009 Sep;32(9):1589-90. doi: 10.2337/dc09-0273. Epub 2009 Jun 5.

TSH-lowering effect of metformin in type 2 diabetic patients: differences between euthyroid, untreated hypothyroid, and euthyroid on L-T4 therapy patients.

Author information

1
Internal Medicine and Endocrinology Unit, Department of Medical and Surgical Sciences, University of Brescia, Brescia, Italy. cappelli@med.unibs.it

Abstract

OBJECTIVE:

To assess the interplay between metformin treatment and thyroid function in type 2 diabetic patients.

RESEARCH DESIGN AND METHODS:

The 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.

RESULTS:

No 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.

CONCLUSIONS:

Metformin 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.

PMID:
19502536
PMCID:
PMC2732148
DOI:
10.2337/dc09-0273
[Indexed for MEDLINE]
Free PMC Article

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