Acetaminophen appears to dull pleasure, not just pain, study finds

Acetaminophen, the pain-relieving ingredient found in Tylenol, Midol, and more than 600 medicines in the United States, can relieve not only pain but pleasure too, a new study suggests.

Acetaminophen is the most common drug in the country, and it has been used for more than 70 years. Previous research suggests the ingredient has a psychological effect in addition to relieving pain, but the current study, published this week in the journal Psychological Science,  is the first to link it to a reduction in positive emotions, said the study authors, from Ohio State University.

“This means that using Tylenol or similar products might have broader consequences than previously thought,” lead study author Geoffrey Durso, a doctoral student in social psychology at The Ohio State University, said in a news release. “Rather than just being a pain reliever, acetaminophen can be seen as an all-purpose emotion reliever.”

To test acetaminophen’s effects on emotion and judgment, researchers conducted two small studies on college students.

In the first study, which involved 82 participants, researchers gave half of the group 1,000 milligrams of acetaminophen and half an identical-looking placebo. They waited an hour for the drug to take effect. Then, they showed participants extremely sad, neutral and very happy photos, and asked them to rate how negative or positive the photo was on a scale of -5 to 5, or extremely negative to extremely positive. Then they showed the participants the photos again and asked them to indicate how much the photo made them feel an emotional reaction on a scale of 0 to 10. Ten indicated an extreme amount of emotion, while zero indicated no emotion.

Researchers found the participants who took the acetaminophen rated the photographs at a lower scale, and had less of an emotional reaction, compared to the placebo group, according to the news release. Based on those results, Durso initially hypothesized that acetaminophen may have a blunting effect on all judgments, not just on those with emotional content.

In a second study, researchers tested that hypothesis. They showed a separate group of 85 people— half who got a placebo, and half who got acetaminophen— the same photos, and had them rate their emotional reactions and indicate their judgments. But they also asked them to report how much of the color blue they saw in each photo.

The surveys including emotional reactions, as well as positive and negative ratings, had results that were consistent with those from the first study. The people who took the acetaminophen rated the photos on a lower scale and had less severe emotional reactions compared to the placebo group. But judgments of blue color content were comparable no matter if participants took the acetaminophen or not, which suggests acetaminophen doesn’t impact overall judgment but does affect emotions, the news release noted.

Next, researchers said they plan to analyze whether other pain relievers like ibuprofen and aspirin have the same effect.

They noted their preliminary findings have an impact on psychological theory. A common belief is that certain factors control how people react to negative experiences. They say that acetaminophen may tap into the sensitivity that makes some people react differently to positive and negative life 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 in the release.