Use of Metformin Tied to Risk of Low Thyroid Hormone Levels

A latest study tied the use of common diabetes drug Metformin to an increased risk of low thyroid-stimulating hormone levels in those with hypothyroidism.

People with hypothyroidism or underactive thyroid display symptoms like weight gain, fatigue and depression. One of the main causes of this condition is deficiency of iodine.

In the latest study, researchers at the McGill University, Montreal, found that Metformin, a commonly used drug to treat type-2 diabetes, increases the risk of low thyroid-stimulating hormone (TSH) level in patients with underactive thyroids. These reduced levels of TSH causes further harm that includes cardiovascular conditions and fractures. The finding is based on the evaluation of the data that included 74,300 patients who received the two common diabetes drugs.

Metformin is an oral anti-diabetic drug that is used to lower blood glucose levels by lowering glucose production in the liver. Several pieces of research have highlighted the health concerns that metformin might help reduce thyroid-stimulating hormone levels.

In this study, the patients were given either Metformin or sulfonylurea, over a 25-year study period. Out of the total 74,300 patients, 5689 had treated hypothyroidism and 59,937 of them had normal thyroid function. Among those with hypothyroidism, there were 495 cases of low thyroid-stimulating hormone per year as compared to 322 in the normal group.

In patients with treated hypothyroidism, Metformin monotherapy was linked with 55 percent increased risk of low TSH levels as compared to the use of sulfonuylurea. However, the use of the drug did not have any effect on those with normal thyroid function.

"The results of this longitudinal study confirmed that the use of metformin was associated with an increased risk of low TSH levels in patients with treated hypothyroidism," said Dr. Laurent Azoulay, Lady Davis Institute, Jewish General Hospital and the Department of Oncology, McGill University, Montréal, Quebec. "Given the relatively high incidence of low TSH levels in patients taking metformin, it is imperative that future studies assess the clinical consequences of this effect."

The finding was documented in the Canadian Medical Association Journal.