Study of the effect of metformin therapy on thyroid function in type 2 diabetic patients

Background Metformin, the most widely used antidiabetic drug, is considered as the cornerstone of type 2 diabetes treatments. Surprisingly, a few years ago, it has been reported that serum thyroid-stimulating hormone (TSH) level in hypothyroid patients decreased in response to metformin therapy and increased again when metformin was discontinued. This study was performed at the Diabetic Outpatient Clinic and Internal Medicine Department at Assiut University Hospital during the period between January and June 2017. Aim The study aimed to assess the effect of metformin treatment on TSH in type 2 diabetic patients with or without thyroid dysfunction. Results A total of 100 patients, with type 2 diabetes mellitus, were enrolled in the study. The patients were divided into two groups: group I included 50 patients on metformin therapy and group II included 50 patients without metformin therapy. Their age was equal to or more than 40 years; their duration of diabetic treatment was equal to or more than 5 years. Conclusion In conclusion, there were significant relationships between TSH levels and metformin therapy, obesity, macroangiopathy, and hyperlipidemia, as the treatment with metformin caused suppression of TSH to subnormal levels without any change in free T4 or frees T3 in diabetic patients.