Acetaminophen pain reliever may also dull your pleasure

Science Nutshell - Tylenol capsules

Next time you take a painkiller, your sensitivity to pain may not be the only thing reduced. You may also be reducing your sensitivity to pleasure

Researchers in the U.S have found that the common pain reliever acetaminophen has a previously unknown side effect of reducing positive emotion.

Previous studies show that acetaminophen reduces both physical and psychological pain, but this new study, published online in the journal Psychological Science, is the first to examine the effect on positive emotions.

Known in many countries as paracetamol, acetaminophen is used in the U.S in over 600 medicines and is the main ingredient in over-the-counter analgesic Tylenol. Each week, 23% of American adults use a medicine containing acetaminophen, according to the Consumer Healthcare Products Association.

Led by Geoffrey Durso, doctoral student in social psychology at Ohio State University, researchers conducted two studies on college students.

The first involved 82 students, half of whom were given 1000 milligrams of acetaminophen and half who took a placebo. After 60 minutes, participants were asked to rate a series of 40 photographs of pleasant, neutral, and unpleasant images on how positive and negative they were, as well as how much the images stirred their emotion.

Neutral images were rated similarly by all participants, but positive images were not rated as highly by those given acetaminophen, and negative images not as low.

“People who took acetaminophen didn’t feel the same highs or lows as did the people who took placebos,” said Baldwin Way, an assistant professor of psychology and a member of the Ohio State Wexner Medical Center’s Institute for Behavioral Medicine Research.

A second study was conducted on 85 people to test whether acetaminophen blunted judgements of everything, not just things with emotional content. The methods were repeated, but participants were also asked how much blue they saw in each photograph.

Results for evaluations and emotional responses were the same as the first study, with those taking acetaminophen not experiencing the same degrees of response. However, judgement of the colour blue was similar in the acetaminophen and placebo groups, suggesting that the blunting effect of acetaminophen relates only to emotional evaluations and not to judgements in general.

This study supports recent psychological theory that common factors determine how sensitive we are not only to bad events in life, as previously theorised, but also to good events. “There is accumulating evidence that some people are more sensitive to big life events of all kinds, rather than just vulnerable to bad events,” Durso said.

Researchers do not know if other pain relievers such as non-steroidal anti-inflammatory drugs like ibuprofen have a similar effect on emotion, but Durso plans to study this too.

Image credit: Wendell on Flickr / Creative Commons attribution license

First published on Science Nutshell, April 17, 2015