A new study is claiming that many Americans are on a common drug that has been connected to dementia, and they don’t even know it.

The blood-thinning drug warfarin is used to fight blood clots, and many Americans use it, but the study claims that it may also raise the risk of dementia, according to an Intermountain Medical Center statement.

The condition warfarin treats is called atrial fibrillation, and it is very common in an aging population — an estimated 20 million use the drug today on a regular basis.

The study examined more than 10,000 patients to see if a link could be found between dementia, warfarin, and atrial fibrillation. The participants in the study were long-term warfarin users and none had a history of dementia. After 7 years, those on warfarin were way more likely to have dementia than those who weren’t: 5.8 percent to 1.6 percent.

“Our study results are the first to show that there are significant cognitive risk factors for patients treated with warfarin over a long period of time regardless of the indication for anticoagulation,” said lead author T. Jared Bunch, MD, director of heart rhythm research at Intermountain Medical Center Heart Institute and medical director for heart rhythm services for the Intermountain Healthcare system.

Bunch described why the study was important.

“First, as physicians we have to understand that although we need to use anticoagulants for many reasons including to prevent stroke in AF patients, at that same time there are risks that need to be considered some of which we are only right now beginning to understand,” he said. “In this regard, only those that absolutely need blood thinners should be placed on them long-term. Second, other medications like aspirin that may increase the blood thinners effect should be avoided unless there is a specific medical need. Finally, in people that are on warfarin in which the levels are erratic or difficult to control, switching to newer agents that are more predictable may lower risk.”