TUESDAY, May 3 (HealthDay News) -- Few Americans bother to read the labels on over-the-counter pain relievers, nor do they pay much attention to the drugs' ingredients, a new study says.

This lack of awareness could be a main reason why acetaminophen overdose is a leading cause of acute liver failure in the United States, according to the researchers at Northwestern University in Chicago.

Acetaminophen, the active ingredient in Tylenol, is in more than 600 over-the-counter (OTC) and prescription medicines.

Researchers interviewed 45 people in six focus groups and found that only 31 percent knew that Tylenol contained acetaminophen, 19 percent realized Advil contained ibuprofen and about the same number knew that Aleve contained naproxen sodium.

About 75 percent knew Bayer contained aspirin and 47 percent knew Motrin contained ibuprofen.

Fewer than half -- 41 percent -- said they read the ingredients on drug labels.

The study appears in the May 3 issue of the American Journal of Preventive Medicine.

The fact that many people don't know acetaminophen is present in OTC products is "incredibly alarming," said senior author Michael Wolf, an associate professor of medicine at Northwestern University Feinberg School of Medicine.

"People may unintentionally misuse these medicines to a point where they cause severe liver damage," Wolf said in a university news release. "It's easy to exceed the safe limit if people don't realize how much acetaminophen they are taking. Unlike prescription products, there is no gatekeeper, no one monitoring how you take it."

He and his colleagues recommend that a universal icon for acetaminophen should appear on the labels of all medicines that contain it.

The study was funded by McNeil Consumer Healthcare, which makes Tylenol. Wolf has worked as a paid consultant to McNeil.

More information

The American Academy of Family Physicians has more about OTC pain relievers.