The effect of metformin on TSH levels in euthyroid and hypothyroid newly diagnosed diabetes mellitus type 2 patients.

INTRODUCTION: Metformin is the first-line oral hypoglycemic agent in the treatment of type 2 diabetes mellitus with a number of positive effects. The aim of the study was to determine the effect of metformin on TSH levels in euthyroid and hypothyroid newly diagnosed diabetes mellitus type 2 patients.

MATERIAL AND METHODS: The study included 255 newly diagnosed diabetes mellitus type 2 drug naive patients, 170 euthyroid patinets, group A, 85 hypothiroid patients, group B, and 80 euthyroid DM type 2 patients on metformin therapy for more than 5 years, group C. Patients in groups A and B began metformin treatment with a dose of 2000 mg/day. We assessed baseline TSH, FT3, FT4 levels and TPOab, in groups A , B and C, and 6 months after initiation of metformin therapy in groups A and B.

RESULTS: There were no differences in FT3 and FT4 levels after 6 months of metformin treatment in all groups. TSH level in Group A showed some reduction after 6 months of metformin therapy, not statistically significant. The only statistically significant change in Group A is the change of TSH level after 6 months in TPOAb positive patients. There was statiscically significant decrease in TSH level after 6 months in group B. There were no significant differences of basal TSH, FT3 and FT4 levels in groups A and B compared to group C.

CONCLUSION: The results show that metformin has TSH lowering effect in patients with type 2 DM and hypothyreoidism, but also in euthyroid TPOab positive, levothyroxine naive patients. We have shown that the TSH lowering effect of metformin is not dependent on long term metformin therapy (Tab. 2, Ref. 18).