Acetaminophen May Blunt Empathy

Batya Swift Yasgur, MA, LSW

April 17, 2019

Acetaminophen appears to reduce feelings of empathy in users, new research suggests.

Investigators showed scenarios of positive experiences to 114 college students who had taken either acetaminophen (1000 mg) or placebo and found that those who had taken acetaminophen experienced less pleasure and empathetic feelings toward the hypothetical characters in comparison with those who had taken placebo.

The ability to recognize pleasure and positivity was unaffected.

"We found that acetaminophen reduced the affective, although not the cognitive, side of empathy," Dominik Mischkowski, PhD, visiting assistant professor, Department of Psychology, Ohio University, Athens, told Medscape Medical News.

"But I would like to strongly emphasize that this doesn't mean you should stop recommending acetaminophen for patients who have pain — pain is a very aversive experience, and a nonprescription painkiller is still a very good tool in the toolbox," he said.

The study was published online March 29 in Frontiers in Psychology.

"Pure" Measure of Emotion

"The data reported in this paper are part of a line of studies looking at how acetaminophen impacts social affect and social behavior — how you feel toward others and how you interact with them," Mischkowski said.

"Our previous work focused on empathy with others who experience negative emotions, in which we compared people taking acetaminophen to those taking placebo in their reactions to scenarios of people experiencing negative events. In that study, we found that acetaminophen reduced empathy for pain," he added.

In the current study, 114 undergraduate students at the Ohio State University were randomly assigned to receive either 1000 mg of acetaminophen (n = 59) or a placebo in liquid form (n = 55).

To measure positive empathy, the investigators gave participants written scenarios. In one scenario, a man proposes to his girlfriend; in another, a man is happy that a woman he is interested in has agreed to a date; in a third, a woman gets a raise at her job; in a fourth, a woman's father comes to her music performance.

Participants completed three measures of positive empathetic perceptions and affective empathy — a one-item measure of perceived positivity, a one-item measure of perceived pleasure, and a six-item measure of personal pleasure.

In addition, while imagining the feelings involved in each scenario, the participants completed an established six-item measure of other-directed empathetic feelings. That tool measured the extent to which the participants felt sympathy, warmth, compassion, soft-heartedness, tenderness, and the degree to which they were moved.

The researchers ruled out baseline differences in affect between the group that received acetaminophen and the group that received placebo by measuring baseline affect and arousal, using the respective one-item subscales of the Self-Assessment Manikin.

To measure whether acetaminophen changed positive empathy through changing general affect, participants completed the Positive and Negative Affect Schedule.

At the end of the study, participants were asked whether they believed they had consumed acetaminophen or the placebo.

"We wanted to control for baseline affect and after people got the drug, since the drug takes time to take effect, and we wanted a pure measure of emotion not 'contaminated' by the drug," said Mischkowski.

Reduced Personal Pleasure

The researchers used Analyses of Variance measures with drug condition (acetaminophen vs placebo) as a between-subjects factor to test whether acetaminophen reduced perceived positivity, perceived pleasure, personal pleasure, and empathetic feelings.

They found that relative to placebo, acetaminophen reduced personal pleasure and empathetic feelings (personal pleasure: F [1110] = 12.38; P < .001; η p 2 = 0.101; empathetic feelings: F[1110] = 11.67; P < .001 η p 2 = 0.096).

In contrast, relative to placebo, acetaminophen did not significantly reduce perceived positivity or perceived pleasure (perceived positivity: F [1110] = 2.44; P= .121; η p 2 = 0.022; perceived pleasure: F[1,110] = 2.74; P = .101; η p 2 = 0.024).

"According to these results, acetaminophen reduced the empathic emotional response when reading about other people having positive experiences but did not affect perceptions about these people's positive experiences," the authors note.

Neither perceived positivity nor perceived pleasure nor both measures in combination mediated the effect of acetaminophen on either reduced personal pleasure or other-directed empathic feelings.

"These findings suggest that empathic perceptions do not account for the effect of acetaminophen on decreased empathic affect," the authors write.

Relative to placebo, consuming acetaminophen did not change general positive or negative affect measured 1 hour after drug administration (just prior to reading the empathy scenarios).

"The mechanism [of the impact of acetaminophen on empathy] is unclear, but there are hypotheses and speculation," Mischkowski said.

"Pain and empathy are complex, just like the brain is complex, so if you are targeting pain, you might also be targeting other areas — and those areas involved in emotional processing, emotional awareness, and acting on emotions are likely candidates," he added.

He also noted an important caveat.

"It is important to put these findings into context and recognize that a lot of people take acetaminophen because they want to treat pain. Pain itself decreases our ability to empathize with other people because it is myopic and self-focused, so we are less able to attend to cues from others — what they need or want. Instead, you are more focused on your own survival," he said.

"In such a framework, if you take away pain, you'd expect a positive effect of acetaminophen [on empathy], but in my studies, I don't induce pain and then see how acetaminophen acts with that and whether it improves social functioning for those who take it for pain," he added.

Empathy Relies on Neural Processes

Commenting on the study for Medscape Medical News, Marija-Magdalena Petrinovic, PhD, lecturer, Department of Forensic and Neurodevelopmental Sciences, Sackler Center for Translational Neuroscience, Camberwell, London, United Kingdom, who was not involved with the research, said the findings "provide further support for the 'shared representations' theory of empathy, which suggests that empathy relies on neural processes similar to those underlying the firsthand experience of a given emotion."

She noted that the "mechanism by which acetaminophen reduces empathy for the pleasurable experiences of other people was not investigated in this interesting study" and that it was "interesting that...acetaminophen exerted effect on affective empathy...but not on cognitive empathy."

This is "suggestive of differential regulation of the underlying neural circuits — in other words, different brain circuits regulate different aspects of empathy — by acetaminophen and thus encourages its further use in proof-of-concept studies aimed at uncovering the neurobiological mechanisms of empathy."

Future studies should compare the use of acetaminophen by healthy, pain-free participants to its use by those with physical pain. They should also involve fMRI measurements of brain activity rather than rely exclusively on self-report, Petrinovic said.

Mischkowski added that he is about to begin a study using imaging to further explore this question.

The study was supported in part by funds from the Ohio State University and the National Center for Advancing Translational Sciences. The authors and Petrinovic have disclosed no relevant financial relationships.

Front Psychol. Published online March 29, 2019. Full text

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