A commonly prescribed drug for type 2 diabetes has potential to increase the risk of heart diseases and various health problems, according to a new Canadian study.

The drug metformin further  lowers the thyroid-stimulating hormone (TSH) levels in patients with underactive thyroids (hypothyroidism), researchers of the study explained. Apart from this, low levels of TSH can result in cardiovascular conditions and fractures.

The most common type of cardiovascular problem Americans face is coronary artery disease that can cause heart attacks. Heart disease is the leading cause of death for both men and women.  More than half of the deaths due to heart disease in 2009 were in men.

For the study, the researchers examined data of 74,300 patients who received metformin and sulfonylurea, another common diabetes drug, over a 25-year period. The team noted 5,689 were treated for hypothyroidism, and 59,937 had normal thyroid function.

The study showed that in the group with hypothyroidism, 495 incidences of low thyroid-stimulating hormone (119.7 per 1000) per year were reported as opposed to 322 in the normal group (4.5 per 1000).

Researcher Dr Laurent Azoulay of McGill University in Montreal, Canada, said that the findings of the study confirmed that the use of metformin was associated with an increased risk of low TSH levels in patients with treated hypothyroidism. "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 research was published in Canadian Medical Association Journal.