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October 1, 2014
Metformin Could Cause Problems for
Hypothyroidism Patients

Montreal—Using metformin to treat type 2 diabetes in patients with hypothyroidism can dangerously lower thyroid-stimulating hormone (TSH) levels and increase the risk of cardiovascular events or bone fractures, according to a new study published in the Canadian Medical Association Journal.

“Given the widespread use of metformin in patients with type 2 diabetes and the potential negative consequences of low TSH,” researchers suggested that their study was necessary to assess the incidence and magnitude in the “natural setting of clinical practice.”

The retrospective study, led by researchers from McGill University, focused on 74,300 patients who received metformin and sulfonylurea over a 25-year period from January 1, 1988, to December 31, 2012. Of those patients, 5,689 had received treatment for hypothyroidism, while another 59,937 had normal thyroid function.

As expected, the group with hypothyroidism had many more incidences of low thyroid-stimulating hormone, 495 or 119.7 per 1,000 annually compared with 322 in the normal group, 4.5 per 1,000.

In patients who had been treated for hypothyroidism, however, metformin monotherapy was associated with a 55% increased risk of low TSH levels compared with sulfonylurea treatment. Patients with normal thyroid function did not appear to be affected.

Study authors note that the increased risk of lower TSH levels was in line with three previous studies. In addition, as those studies also found, the risk appeared to be highest, 130%, in the 90 to 180 days after treatment initiation.

“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 co-author Laurent Azoulay, PhD. “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.”

U.S. Pharmacist Social Connect