A new study uncovers an alarming risk.

You may want to think twice before you pop a pill to get some relief from the cold or flu: Taking some popular, over-the-counter pain relievers when you’re sick can raise your risk of a heart attack, a new study in the Journal of Infectious Diseases found.

After analysing data from nearly 10,000 patients, the researchers discovered that taking a non-steroidal anti-inflammatory drug (NSAID, like ibuprofen) and having a respiratory infection like a cold or flu both separately raised the risk of experiencing a heart attack.

But the combination of taking NSAIDs while sick with a cold or flu was the most dangerous: People who popped the pills to combat their respiratory illness increased their chances of having a heart attack by 3.4-fold.

That’s a problem, since many multi-symptom, over-the-counter cold and flu medications contain NSAIDs—so you might be taking them without even realizing it.

Here’s how the combo might be putting your heart at risk: Infections may spark changes in your body, leading to the production of inflammatory proteins and thickening your blood—potentially causing blood clots, the researchers say. Along with raising your blood pressure, NSAIDs may also affect the way your blood platelets clump together. The meds may constrict your blood vessels, too.

So using NSAIDs when your body is fighting a sickness likely only compounds effects of each, leading to a greater heart attack risk.

Because this was an observational study, the researchers can’t say for sure whether the combo of NSAIDs and a respiratory infection can actually cause a heart attack. But more research needs to be done, especially to determine if there are specific kinds of NSAIDs that may be more dangerous than others—and if certain populations are at greater risk.

In the meantime, talk to your doctor about which meds to take if you’re knocked down with a cold or flu. While the study didn’t look at acetaminophen—the ingredient used in Tylenol—it may be a safer alternative for pain relief during cold or flu, since it works differently than NSAIDs, the researchers said in a press release.