Study Effects Of Metformin On Thyroid Functions In Patients Of Type 2 Diabetes Mellitus

Abstract

Metformin, the most widely used oral hypoglycemic agent, remains the cornerstone of Type 2 Diabetes Mellitus (T2DM) management. Recent evidence suggests that metformin may influence thyroid function by reducing serum Thyroid-Stimulating Hormone (TSH) levels in diabetic patients. This study aimed to compare the effects of metformin-based and non–metformin-based therapies on thyroid function in patients with T2DM.

Methodology: A case-control observational study was conducted at a tertiary care center after obtaining approval from the Institutional Ethics Committee. A total of 140 adults with T2DM aged above 18 years were enrolled. Group 1 included patients on metformin therapy for more than six months, while Group 2 included patients on other antidiabetic medications without metformin. Patients with known thyroid disorders, those on thyroid-affecting drugs, pregnant women, and individuals with major systemic illnesses were excluded. Thyroid profile parameters—TSH, Free Triiodothyronine (FT3), and Free Thyroxine (FT4)—were measured using the Vitros 5600 analyzer at baseline, 3 months, and 6 months. Statistical analysis was performed to compare thyroid function changes between the two groups.

Results: The mean age of participants was 56.08 ± 14.59 years. In the metformin group, FT3 and FT4 levels showed a mild, non-significant increase, while TSH levels demonstrated a significant decline from 2.86 ± 2.43 µIU/mL to 1.41 ± 0.94 µIU/mL (p < 0.0001), indicating a suppressive effect of metformin on TSH secretion. The non–metformin group exhibited non-significant changes in FT3 and FT4 and a non-significant reduction in TSH from 6.93 ± 24.77 µIU/mL to 2.97 ± 2.67 µIU/mL (p = 0.1866).

Conclusion: Metformin therapy significantly reduces serum TSH levels in patients with Type 2 Diabetes Mellitus without affecting FT3 and FT4 concentrations. These findings highlight the importance of regular thyroid function monitoring in diabetic patients receiving metformin, particularly those with pre-existing thyroid disorders. Further research with larger sample sizes and longer follow-up periods is warranted to elucidate the mechanisms underlying metformin’s influence on thyroid regulation.