As many as one-quarter of people with atrial fibrillation who have a low risk of stroke are given blood-thinning drugs they likely don't need, a new study contends .

Atrial fibrillation -- a common form of irregular heartbeat -- can cause blood clots. Those blood clots can then travel to the brain and cause a stroke. To prevent this from happening, many people with atrial fibrillation are prescribed blood thinners.

However, because the drugs also have a risk of causing excessive bleeding, they generally aren't recommended for people with atrial fibrillation who have the lowest risk for stroke, the study authors explained.

The study included information from nearly 11,000 atrial fibrillation patients across the United States. They were all younger than 60. They were also all considered to have a low risk of stroke, according to the researchers.

Still, the study found about 25 percent of them were prescribed blood thinners, contrary to current treatment guidelines.

"Practitioners who prescribe blood thinners need to be diligent about weighing the risks and benefits of these medications," study lead author Dr. Jonathan Hsu from the University of California, San Francisco, said in a university news release.

"In those patients with no risk factors for stroke, the risk of bleeding likely outweighs the benefit of stroke reduction. The fact that blood thinners were prescribed to so many patients with no risk factors for stroke is a wake-up call that we need to do better for our patients," Hsu concluded.

Men were more likely to be prescribed blood thinners than women, as were older patients and overweight patients without stroke risk factors, according to the findings in a research letter published online April 13 in the journal JAMA Internal Medicine.

The findings show that doctors may not be fully aware of the potential risks of these drugs, or the particularly low risk of stroke in certain atrial fibrillation patients, the researchers said.

Study senior author Dr. Gregory Marcus noted, "The irony is that there is a general push to get providers to prescribe these drugs, and they are also generally under-prescribed among many atrial patients who actually need them." Marcus is director of clinical research in the division of cardiology at UCSF.

"Our study suggests people are trying to do the right thing, but due to a lack of understanding of some of the critical nuances, go too far in that direction in low-risk patients," he added.