Doctors rely on patients to accurately tell them what medications they’re taking, but a recent study found that many patients can’t name a single drug they’ve been prescribed.

Researchers from Northwestern University’s Feinberg School of Medicine asked 119 patients with an average age of 55 to name the medications listed in their charts. Nearly 50 percent could not name a single one.

“It was worse than we expected,” says Dr. Stephen Persell, assistant professor of medicine at the school. “It means that doctors can’t ask patients to tell them the medications they are taking for chronic conditions such as hypertension. It’s very hard to get at the truth of what medications the patient is actually taking.”

The doctors suggested patients bring their prescription bottles with them to their appointments so that doctors can get accurate information and also review the medications to catch dangerous combinations.