The Effect of Metformin on Thyroid Nodules

Introduction: Thyroid nodules are highly prevalent.The role of insulin resistance in thyroid nodule formation has recently gained attention.While several studies have explored the relationship between metformin and insulin resistance, limited research has assessed the effect of metformin therapy on thyroid nodule volume and number.This study investigated the effect of metformin on the size and number of thyroid nodules.Methods: A total of 240 euthyroid women with thyroid nodules were divided into four groups.Group 1 received levothyroxine 100 g/day, Group 2 received metformin 500 mg twice daily, Group 3 received a combination of both drugs for three months, and Group 4 served as the control group with no treatment.Thyroid ultrasound was performed at baseline and after three months.Statistical analyses included the Kruskall-Wallis, Wilcoxon, and Chi-square tests, examined the differences of the size of thyroid nodules and the mean of thyroid hormones levels between groups, for Each group included 60 people and to compare the percentage of differences between the groups, respectively.Also P value less than 0.05 was considered meaningful.Results: Results showed no statistically significant differences in thyroid hormone levels after treatment among the three groups except the levothyroxine group.Additionally, only the levothyroxine group showed a significant post-treatment decrease in TSH and increase in T4.Thyroid nodule size significantly decreased in the levothyroxine group and the levothyroxinemetformin combination group compared to the metformin-alone and control groups.Conclusions: This study indicates that metformin does not reduce the size of thyroid nodules, contradicting studies suggesting its potential antineoplastic effects on the thyroid.However, the study duration may be insufficient for definitive conclusions, necessitating further high-quality studies with larger sample sizes and longer follow-up periods.