An unexpected side effect of one of the most popular over-the-counter painkillers.
Every week, about 52 million American adults (23 percent) use a medicine containing acetaminophen, which is the main ingredient in the popular painkiller Tylenol, according to the Consumer Healthcare Products Association.
Most people don’t think twice before grabbing a Tylenol to help relieve a headache or a muscle ache, but researchers at The Ohio State University have found taking acetaminophen may be affecting individuals in more ways than they bargained for. In two separate experiments, the researchers found that taking acetaminophen can reduce the user’s ability to empathize with other people’s pain and suffering.
"These findings suggest other people's pain doesn't seem as big of a deal to you when you've taken acetaminophen," co-author Dominik Mischkowski, with the National Institutes of Health, said in a media statement.
Baldwin Way, assistant professor of psychology and member of the Ohio State Wexner Medical Center's Institute for Behavioral Medicine Research, has conducted previous research that found that acetaminophen blunts positive emotions like joy.
"We don't know why acetaminophen is having these effects, but it is concerning," said Way.
The first experiment involved 80 college students, and in the beginning, half of the students drank a liquid containing 1,000 mg of acetaminophen (the equivalent of two extra-strength Tylenols). The other group drank a placebo solution that contained no drug. The students weren’t aware of which group they had been placed in.
After an hour had passed, the participants were asked to read eight short scenarios in which someone suffered some type of pain. For instance, in one scenario, a person suffered from a knife cut that went down to the bone, and in another, a person was experiencing the death of his father.
The volunteers then rated the pain level experienced by each person from 1 (no pain at all) to 5 (worst possible pain). Overall, the participants who took acetaminophen rated the painful scenarios to be less severe than those who took the placebo.
In the second experiment, 114 college students participated — again, half took acetaminophen and half took a placebo. The experiment had two parts.
In the first, participants received four two-second blasts of white noise, ranging from 75 to 105 decibels. They rated how painful the white noise blasts were on a scale of 1 (not unpleasant at all) to 10 (extremely unpleasant), and then were asked to imagine how much pain these noise blasts would cause another study participant.
Compared to the volunteers who took a placebo, the acetaminophen-affected participants rated their own pain as less severe, but also thought the noise blasts would be less unpleasant for others.
"Acetaminophen reduced the pain they felt, but it also reduced their empathy for others who were experiencing the same noise blasts," Mischkowski said.
In the other part of the experiment, the participants socialized with each other briefly before watching an online game that supposedly involved three of the people they’d just met. In the online game, two of the people they had met excluded the third person from the activity, and the participants were asked to rate how much pain the other students in the game felt from the interactions.
"In this case, the participants had the chance to empathize with the suffering of someone who they thought was going through a socially painful experience," Way said.
"Still, those who took acetaminophen showed a reduction in empathy. They weren't as concerned about the rejected person's hurt feelings."
Way says that these findings make sense in light of a 2004 study that scanned the brains of people both as they were experiencing pain and while they were imagining other people’s feelings of pain. The results showed that the same part of the brain was activated in both instances.
"In light of those results, it is understandable why using Tylenol to reduce your pain may also reduce your ability to feel other people's pain as well," he said.
The researchers plan to continue studying how acetaminophen affects people’s emotions and behavior, and are also beginning to investigate whether ibuprofen, another common pain reliever, has similar effects.
The results are published in the journal Social Cognitive and Affective Neuroscience.