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. 2025 Jul;14(7):2941-2944.
doi: 10.4103/jfmpc.jfmpc_75_25. Epub 2025 Jul 21.

To study effects of metformin on thyroid functions in type-2 diabetes mellitus in patients attending OPD at Government Medical College, Bidar

Prashant Patil  1 , Sachin Gudage  1 , Mahesh B Tondare  2 , Sangamesh B Tondare  3 , Praveen Ganganahalli  4
Affiliations

To study effects of metformin on thyroid functions in type-2 diabetes mellitus in patients attending OPD at Government Medical College, Bidar

Prashant Patil et al. J Family Med Prim Care. 2025 Jul.

Abstract

Introduction: Metformin is one of the most used diabetes treating agents and has proved to be very effective, with a wide spectrum of efficacy, safety as well as being as agent that works at different spots in diabetes pathogenesis paradigm. Recently it has been reported that metformin is able to interfere with thyroid hormone profile, by decrease in the serum levels of thyrotropin (TSH) to subnormal levels in hypothyroid patients in stable levothyroxine (L-T4) treatment.

Objectives: To study and compare the effect of metformin and non-metformin composed treatment of type-2 diabetes mellitus on thyroid functions.

Methods: Comparative observational study was conducted among diabetic patients taking metformin as study and taking antidiabetic other than metformin as control group and analysed for the thyroid profile (TSH, fT3, fT4). Total 70 patients including both group from tertiary care teaching hospital were enrolled in to the study after taking informed verbal consent.

Observations: The present study demonstrates that while the study group's fT3 and fT4 levels were lower than those of the control group, diabetic patients on non-metformin medication had statistically higher TSH (2.05 ± 0.15 mIU/mL vs. 2.35 ± 0.18 mIU/mL) levels than those taking metformin.

Conclusion: Thyroid-stimulating hormone (TSH) levels may be somewhat or not at all decreased by metformin. Thyroid function monitoring is crucial for diabetic patients using metformin, particularly if they already have thyroid problems.

Keywords: T3; T4; TSH; thyroid function; type-2 diabetes.

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Conflict of interest statement

There are no conflicts of interest.

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