Taking a popular painkiller may be linked to decreased ability to empathize with others' suffering, a new study suggests.

The people in the study who took acetaminophen (sold as Tylenol and various generic labels) showed lower levels of empathy toward other people who talked about feeling physical and emotional pain than those who took a placebo, the researchers found.

"Acetaminophen can reduce empathy as well as serve as a painkiller," study co-author Dominik Mischkowski, a postdoctoral fellow at the National Institutes of Health who was a Ph.D. student at The Ohio State University at the time of the research, said in a statement. [7 Bizarre Drug Side Effects]

Acetaminophen is the most common active ingredient used in drugs sold in the United States, and is found in more than 600 medicines, according to the Consumer Healthcare Products Association. Each week, about 52 million people in the United States use a medicine that contains acetaminophen, according to the association.

In one experiment in the study, 40 healthy college students drank a liquid containing 1,000 milligrams of acetaminophen (the maximum recommended dose of Tylenol for adults over the course of a 24-hour period is 3,000 milligrams, or 6 pills per day), and another 40 college students drank a placebo solution without the drug. After one hour, the students read eight short scenarios in which people suffered some sort of physical or emotional pain. For example, one scenario was about someone who had experienced a knife cut that went down to the bone, and another was about someone else mourning the recent death of his father.

Then, the people in the study rated the intensity of pain that they thought the people described in the scenarios had experienced. It turned out that the people who took acetaminophen rated the pain of the people in the scenarios to be less severe than the people who took the placebo did. [5 Surprising Facts About Pain]

In the second experiment, the researchers looked at 114 college students, who took either acetaminophen or a placebo. The students received four 2-second blasts of loud noise and rated how unpleasant the blasts were. They were also asked to rate how unpleasant the same noise blasts would be to other anonymous people.

It turned out that the people who took the acetaminophen rated the blasts as less unpleasant to both themselves and other people compared with people who took the placebo, according to the study, published in May in the journal Social Cognitive and Affective Neuroscience.

It is not clear why, exactly, the drug appears to be linked to lower levels of empathy, and more research is needed to examine the potential mechanism behind the link, the researchers said.

The study also had some caveats, the researchers said. For example, the people in the study were healthy and were not experiencing actual physical pain, said study co-author Baldwin Way, a psychology professor at The Ohio State University.

"That might be a slightly different context than someone who is taking this drug for a headache or a back ache or some sort of pain," he told Live Science.

Therefore, it is not clear if the link between taking the drug and lower empathy levels would also be present in people taking these drugs to deal with physical pain, he said.

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