"Allowing these drugs to be purchased without a prescription, and without any advice or restrictions, sends a message to the public that they must be safe," Gunnar H. Gislason, author of the study and professor of cardiology, said in a news release. "The findings are a stark reminder that NSAIDs are not harmless."
To come up with the results, researchers used the Danish Cardiac Arrest Registry to collect the medical history of nearly 30,000 patients who had suffered a heart attack outside of the hospital from 2000 to 2010.
They also examined all NSAID prescriptions filled at Danish pharmacies since 1995.
According to Time, ibuprofen and naproxen, both available over the counter in the United States as Advil and Aleve, require prescriptions in Denmark.