Physical pain and the distress that comes with social rejection have been traced to the same area of the brain. This intriguing connection may shed some light on how acetaminophen (brand name Tylenol) may also affect the brain.

Accumulating research suggests that, along with inhibiting physical pain, acetaminophen may also act on emotions and have other neurological effects.

One of the latest studies, conducted by researchers from the University of Toronto and the University of British Columbia, suggests the popular painkiller may even inhibit the brain response associated with making errors.

Acetaminophen May Make It Harder to Recognize Errors

Sixty study participants were asked to complete a fast-moving target-detection task while hooked up to an electroencephalogram (EEG), which measures electrical activity in the brain.

When the letter F flashed on a screen, they were asked to press a Go button. When the letter E flashed on the screen, they were told to refrain from hitting the button.

Half of the participants took 1,000 milligrams (mg) of acetaminophen (a typical maximum dose) prior to completing the task, and notable changes were displayed on the EEG.

The researchers analyzed brain waves called Error Related Negativity (ERN) and Error Related Positivity (Pe). Both ERN and Pe increased when the participants made errors, but Pe was smaller among those who took acetaminophen.

This suggests the drug inhibits the brain’s ability to detect the error or, more specifically, may reduce the distress associated with errors so you’re less likely to pay attention to them. Lead author Dan Randles, a postdoctoral fellow in the Psychology department at University of Toronto, said in an interview with Forbes:¹

“Very recent work in the last few years has suggested that acetaminophen not only affects physical pain, but also feelings of social rejection, uncertainty and evaluative processing.

… This study is the first to provide compelling evidence that acetaminophen is affecting all of these symptoms by reducing the distress associated with any kind of cognitive conflict; whether the source is physical, social or more abstract.”

The study also revealed a surprise finding — that those taking acetaminophen also made more errors. The researchers are planning to look further into whether the drug may increase distraction or mind wandering, thereby leading to increased errors.

Tylenol May Dull Feelings of Personal Distress and Social Rejection

Past research has also unveiled subtle cognitive effects associated with acetaminophen. In 2010, for instance, research found that acetaminophen reduces the pain of social rejection.²

Compared to those taking a placebo, those who took acetaminophen daily for three weeks had reduced neural responses to social rejection in brain regions associated with distress caused by social pain and physical pain (dorsal anterior cingulate cortex, anterior insula).

Then, in 2013, a prior study by Randles and his colleagues found acetaminophen led to changes in the way people made moral judgments, which was used as a measure for personal distress.³

In addition to social rejection, acetaminophen may blunt distress associated with more abstract concepts. The researchers told Live Science:⁴

“When people feel overwhelmed with uncertainty in life or distressed by a lack of purpose, what they’re feeling may actually be painful distress …

We think that Tylenol is blocking existential unease in the same way it prevents pain, because a similar neurological process is responsible for both types of distress.”

Acetaminophen Might Dull Your Happiness, Too

Acetaminophen’s apparent dulling effect on your emotional responses might work for better or for worse, watering down not only negative emotions but also positive ones. Researchers showed emotional photos to college students who had either taken a 1,000-mg dose of acetaminophen or a placebo.

Those who took the painkiller had more muted emotional responses to both negative and positive images.5 According to the researchers:

“Participants who took acetaminophen evaluated unpleasant stimuli less negatively and pleasant stimuli less positively, compared with participants who took a placebo.

Participants in the acetaminophen condition also rated both negative and positive stimuli as less emotionally arousing than did participants in the placebo condition …

These findings suggest that acetaminophen has a general blunting effect on individuals’ evaluative and emotional processing, irrespective of negative or positive valence.”

As for why the drug might dull your emotions, the researchers suggested it might alter brain activity, such as the activity of serotonin, reduce inflammatory signaling or decrease activation in brain areas linked to emotional processing.6

Although they weren’t tested, the researchers believe other pain relievers, including aspirin or ibuprofen, might have similar emotion-blunting effects.