Acetaminophen, commonly known by the trade name Tylenol, is an ingredient in more than 600 prescription and over-the-counter medicines.

Unlike local signal blocking painkillers, such as the Novocain used in the dentist’s office, acetaminophen acts globally to reduce the brain’s ability to process pain.

empathy and opiods

And the ability to feel pain, as existing research has found, is an important part of being able to empathize with pain observed in other people.

This raises a crucial question: Does acetaminophen actually block empathy for other’s pain?

Until last year, no study had ever directly examined the potential connection.

Last month, however, scientists at The Ohio State University (OSU) published new research in the journal Social Cognitive and Affective Neuroscience exploring the possibilities.

Read More: Bipolar Disorder and a Lack of Empathy »

I Feel You

The scientists recruited 80 university students to participate in two studies.

In both studies, each student was given a sweetened drink. Half the drinks contained a placebo. The other half contained 1,000 mg of acetaminophen. That’s the same amount as found in two tablets of extra-strength adult Tylenol, a common dose.

In the first experiment, the students read short stories about hypothetical people experiencing physical pain (like cutting a finger) or social pain (such as the death of their father). Then, they rated how much pain they imagined the person in the story was feeling.

The second experiment tried to make the perceived pain seem more vivid. The students observed a computer simulation — which they were told was real — of three simulated students playing a game of virtual catch.

As they watched, two of the simulated students threw the virtual ball to each other more and more, and to the third student less and less. Eventually, the third student was completely excluded from the game.

This type of experiment, called a social ostracism condition, is a well-established way to induce social pain. The students then rated how much pain they thought the excluded student was experiencing.

To control for acetaminophen’s impact on the raw experience of pain, the second experiment also subjected the students to a series of loud, painful noises. The students rated their own pain after hearing the noise blasts. They then rated the pain of an imagined student receiving the same noise blasts.

In both experiments, the students who drank the acetaminophen-laden beverage rated other people’s pain as less severe than did the students who drank the placebo beverage.

However, the effect varied widely from student to student. Some were sensitive to acetaminophen’s effects while others showed no differences at all.

“I want to emphasize that our effects are moderate,” Dominik Mischkowski, Ph.D., lead author on the study and former graduate student at OSU, told Healthline. “It's not that acetaminophen totally gets rid of empathy. It just reduces it.

He explained, “This is not a paper about apathy. It's a paper about empathy. It's not that people stop caring about anything. It’s just that they seem not to care about the pain of other people.”

Mischkowski worries that even a modest effect could influence some people’s behavior.

“How does acetaminophen actually influence how people interact with each other in an interpersonal conflict?” he questioned. “When you have an argument with your spouse? When you have a difficult conversation with your supervisor or the person you're mentoring? How does it affect the empathy of someone in medical position toward a patient? That would be very interesting to look at, I think. We don't have the data yet.”

Now a postdoctoral research fellow at the National Institutes of Health, Mischkowski is working on follow-up research to see how acetaminophen might affect behavior itself.

Read More: Why Does Everyone Care So Much about Cecil the Lion? »

Pain on the Brain

Mischkowski’s findings bring up the next question: What’s going on in the brain?

Does acetaminophen blunt only pain, which would in turn damage our ability to understand pain when it occurs in others?

Or does acetaminophen also block empathy itself?

Although Mischkowski didn’t have the opportunity to collect brain data on the students in his study, research from other scientists may shed light into what’s going on here.

A 2004 study compared brain activity in subjects who both experienced pain directly and were informed that a loved one was in pain. Both direct pain and empathic pain activated the insula and anterior cingulate cortex (ACC) in both sides of the brain, suggesting that the two experiences share common underpinnings.

Direct pain had an additional, broader effect. It activated a greater portion of the insula and ACC in just the side of the brain that was receiving the pain signal. It also activated that side’s sensory cortex, which receives the raw incoming signals of physical sensations in the body.

Then, a study from 2010 looked at how acetaminophen blunts pain from social rejection. The researchers found that the drug reduced activity in the same regions of the brain involved in empathic, but not direct, pain.

Together, these findings suggest that acetaminophen has a greater impact than simple physical pain reduction. It’s dampening our emotions.

And emotions share real estate with other functions in the brain.

“The insula and the ACC are very big regions in the [brain],” Mischkowski pointed out. “Their response is for pain, but also for other things.”

For example, he explained, the ACC also is involved in error detection.

“So the question is, how specific [are] the effects of acetaminophen? Does it just dull pain, or does it dull other things? Acetaminophen might not just impact empathy, but also … might dull a lot of functions that are related to these pain regions,” he said.

Tor Wager, Ph.D., professor of psychology and neuroscience at the Institute of Cognitive Science at the University of Colorado, Boulder, explained more.

“Acetaminophen affects a spectrum of social, [emotional], and decision processes whose boundaries are just beginning to be characterized,” he told Healthline. “Essentially, all drugs in common use have multiple, diverse effects. For example, beta-blockers can affect anxiety and they [also] affect the function of fat cells, which is one reason obesity is a common side effect. Often, when one effect — and commercial use — for a drug is established, we assume we understand these drugs, but we don’t.”

Wager’s lab is gathering more neuroscientific evidence to tell apart personal vs. vicarious pain which is set to publish later this year.

Read More: Mars and Venus: How Men and Women Process Emotions »

But Mom, Everyone’s Doing It

Even if acetaminophen’s effects are modest and varied, it could still be having a widespread impact simply from the sheer number of people taking the drug.

Almost a quarter of adults in the United States use a prescription or over-the-counter medicine containing acetaminophen. That’s over twice the number of American adults who experience chronic pain. In 2005, more than 28 billion doses of products containing acetaminophen were sold in the United States.

Acetaminophen has come under fire in recent years because of its inclusion in so many medicines. Patients who are taking products containing acetaminophen risk overdosing. That phenomenon sent 56,000 people to the emergency room, 26,000 people to the hospital, and 458 people to the grave between 1990 and 1998.

Acetaminophen overdose is the leading cause of acute liver failure, causing nearly half of all acute liver failure cases.

If acetaminophen can blunt empathy, then it’s possible that a large number of people are being subtly numbed out by the drug — not just to others’ pain, but also to positive emotions, suggests research from the same lab that Mischkowski worked in at OSU.

“I think that these side effects that are potentially concerning,” said Mischkowski. “This is a medication that a lot of people take. It's an overarching goal to figure out whether taking painkillers actually influences how you interact with other people. We don't know how bad the effects actually are on a larger, societal level.”

Wager shares the concern. “The picture this study paints, along with other recent work, is that acetaminophen can influence [emotions] in small but fundamental, and possibly diverse, ways,” he explained. “Empathy is so important for healthy relationships and a healthy society. When we experience pain and threat, it is possible that we empathize with others less.

However, both scientists also agree that it’s important not to take these findings out of context.

“If you take acetaminophen, you shouldn't be scared about these side effects,” Mischkowski said. “You should be aware that when you take acetaminophen for pain relief, you also might, at the same time, numb your empathy toward others. Be aware of it, and take it into context. You shouldn't just say, ‘OK, I should not take acetaminophen anymore.’ It's still an important painkiller.”

Wager concluded, “There are costs and benefits to everything, and the right answer for a given person is what those costs and benefits are anticipated to be. More broadly, we need to try to understand drug effects on multiple brain and body systems, without getting lured down the garden path of considering only one system.”