Does Metformin Lower Thyroid-Stimulating Hormone Levels?

Patients with underactive thyroid function that use metformin—used to treat type 2 diabetes—could be at risk for low levels of the thyroid-stimulating hormone (TSH), according to a recent study.

According to researchers, low TSH levels could lead to cardiovascular complications and other ailments.
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For the study, researchers (using Cox proportional hazards models) evaluated the 25-year data on 74,300 patients who were administered metformin monotherapy and sulfonylurea monotherapy and compared the results.

Among the participants, 5689 were treated for hypothyroidism and 59,937 had normal levels (euthyroid). 

In the group of participants with hypothyroidism, researchers noted 495 instances of low TSH every year (incidence rate 119.7/1000) compared to only 322 cases among euthyroid participants (incidence rate 4.5/1000).

Overall, researchers observed a 55% heightened risk of low TSH levels in patients with hypothyroidism also using metformin compared to those using sulfonylurea.

Investigators further noted that the euthyroid group remained unmarred after use of metformin and sulfonylurea.

The complete study is published in the September issue of the Canadian Medical Association Journal.

-Michelle Canales

Reference:

Fournier JP, Yin H, Yu OHY, Azoulay. Metformin and low levels of thyroid-stimulating hormone in patients with type 2 diabetes mellitus. CMAJ. 2014 Sept [epub ahead of print] doi: 10.1503/cmaj.140688.