Aspirin is a popular drug for people who’ve never had a heart attack or stroke and would like to keep it that way.

But for more than one in 10 people who do so, aspirin could do more harm than good, a new study suggests.

Among 68,808 patients being treated by cardiologists around the U.S., 7,972 of them were taking aspirin despite having a very low risk of having a heart attack or stroke in the next 10 years. In other words, 11.6 percent of patients were taking the drug “inappropriately,” according to a study published Monday in the Journal of the American College of Cardiology.

Aspirin averts heart attacks and strokes by preventing the formation of blood clots. Clots are made up of blood cells called platelets, which stick together with the help of an enzyme known as cyclo-oxygenase, or COX. But aspirin prevents COX from doing its job.

While that’s useful in the fight against cardiovascular disease, it can be dangerous in other ways. When blood can’t clot easily, people run the risk of excessive bleeding. In the brain, that can lead to a hemorrhagic stroke.

That’s why experts recommend aspirin therapy only for people with a significant risk of a clot-related problem. That includes pretty much everyone who has already suffered a stroke or heart attack.