The Journal of Clinical Endocrinology & Metabolism; 91(1):225–227

Thyrotropin Suppression by Metformin
Robert A. Vigersky, Amy Filmore-Nassar, and Allan R. Glass Endocrinology Service, Walter Reed Army Medical Center, Washington, DC 20307

This study noted that patients on metformin (Glucohage) had a subsequent suppression in TSH level without a change in serum thyroid levels, demonstrating that there is often associated a thyroid resistance in patients with insulin resistance that is partially improved with metformin. This study adds to the mounting evidence that due to a variety of factors, including tissue altered metabolism of thyroid and thyroid hormone resistance, standard thyroid function tests do not correlate with tissue effect of thyroid.