Differences in TSH lowering effect of metformin in hypothyroid and euthyroid type 2 diabetic patients
Dragan Dimic, Milena Velojic Golubovic, Sasa Radenkovic, Danijela Stojic & Slbodan Antic
Objectives: It has been reported that metformin administration lowered TSH levels in patients with type 2 diabetes mellitus and hypothyreosis. The aim of the study was to investigate effect of metformin on TSH levels in type 2 diabetic patients with primary hypothyroidism and also in patient with type 2 diabetes mellitus only.
Methods: We included in our study 9 type 2 diabetic patients with primary hypothyroidism on stable l-thyroxine replacement doses and 9 euthyroid type 2 diabetic patients. In all patients 2000 mg daily metformin therapy was initiated. Thyroid hormones, FT3 and FT4, and TSH was measured in all subjects at baseline and 3 months after metformin therapy initiation.
Results: There was decrease of TSH levels in all hypothyroid diabetic patients after metformin administration. The mean TSH levels decreased from 2.86±0.97 mU/l on baseline to 0.96±0.49 mU/l after three months, which has statistical significant, P<0.05. In euthyroid type 2 diabetic patients the level of TSH show no significant difference, TSH at baseline was 2.05±1.32 mU/l and after three months TSH 2.21±1.44 mU/l. There was no significant changes in FT3 and FT4 levels in both groups.
Conclusion: Our results shows that in subjects with primary hypthyreoidism and diabetes mellitus type 2 metformim administration is associated with significantly lower TSH levels after three months of therapy, without signs of clinical and biochemical hyperthyreoidism. The mechanism of thyreotropin suppression by metformin is not clear and there is several possible explanations. Metformin has no effect on TSH levels in euthyroid diabetic patients.