Researchers studying the commonly used pain reliever acetaminophen found it has a previously unknown side effect: It blunts positive emotions.
In the study, participants who took acetaminophen reported less strong emotions when they saw both very pleasant and very disturbing photos, when compared to those who took placebos.
Acetaminophen, the main ingredient in the over-the-counter pain reliever Tylenol, has been in use for more than 70 years in the United States, but this is the first time that this side effect has been documented.
Previous research had shown that acetaminophen works not only on physical pain, but also on psychological pain. This study takes those results one step further by showing that it also reduces how much users actually feel positive emotions, said Geoffrey Durso, lead author of the study and a doctoral student in social psychology at The Ohio State University.
“This means that using Tylenol or similar products might have broader consequences than previously thought,” Durso said.
“Rather than just being a pain reliever, acetaminophen can be seen as an all-purpose emotion reliever.”
Durso conducted the study with Andrew Luttrell, another graduate student in psychology at Ohio State, and Baldwin Way, an assistant professor of psychology and the Ohio State Wexner Medical Center’s Institute for Behavioral Medicine Research. Their results appear online in the journal Psychological Science.
Way said people in the study who took the pain reliever didn’t appear to know they were reacting differently. “Most people probably aren’t aware of how their emotions may be impacted when they take acetaminophen,” he said.
Acetaminophen is the most common drug ingredient in the United States, found in more than 600 medicines, according to the Consumer Healthcare Products Association, a trade group.
Each week about 23 percent of American adults (about 52 million people) use a medicine containing acetaminophen, the CHPA reports.
There were two studies of college students. The first involved 82 participants, half of whom took an acute dose of 1000 milligrams of acetaminophen and half who took an identical-looking placebo. They then waited 60 minutes for the drug to take effect.
Participants then viewed 40 photographs selected from a database (International Affective Picture System) used by researchers around the world to elicit emotional responses.
The photographs ranged from the extremely unpleasant (crying, malnourished children) to the neutral (a cow in a field) to the very pleasant (young children playing with cats).
After viewing each photo, participants were asked to rate how positive or negative the photo was on a scale of -5 (extremely negative) to +5 (extremely positive). They then viewed the same photos again and were asked to rate how much the photo made them feel an emotional reaction, from 0 (little or no emotion) to 10 (extreme amount of emotion).
Results in both studies showed that participants who took acetaminophen rated all the photographs less extremely than did those who took the placebo.
In other words, positive photos were not seen as positively under the influence of acetaminophen and negative photos were not seen as negatively.
The same was true of their emotional reactions.
“People who took acetaminophen didn’t feel the same highs or lows as did the people who took placebos,” Way said.
For example, people who took the placebo rated their level of emotion relatively high (average score of 6.76) when they saw the most emotionally jarring photos of the malnourished child or the children with kittens.