In the latest study, researchers at McGill University in Montreal found that Metformin, a commonly used drug to treat type-2 diabetes, increases the risk of low thyroid-stimulating hormone level in patients with underactive thyroids. In this study, 74,300 patients were given either Metformin or sulfonylurea, over a 25-year study period. In patients with treated hypothyroidism, Metformin monotherapy was linked with 55% increased risk of low TSH levels as compared to the use of sulfonuylurea. Via Science World Report. Posted September 26, 2014.