A recent study on the psychological effects of acetaminophen (or paracetmol)–the active ingredient in Tylenol–has been making headlines lately. This study, however, is a recent addition to a growing body of research showing the surprising psychological effects of this drug. I’ll cover the new study in a minute, but I thought it was worth taking the opportunity to review the evidence that’s come out over the last five or so years about this seemingly straightforward drug.

By way of quick introduction, it’s worth noting that acetaminophen is most famous for its pain killing abilities. Got a headache? Some other bodily pain? A quick trip to the drug store will sort you out. You’ve probably got a bottle of it sitting in your bathroom somewhere.

It’s a popular little drug, and according to recent estimates, some 50 million Americans take the stuff each week. Until recently, though, many assumed that this was a drug with purely physical effects, targeting the bodily sensastion of pain. These days, that notion has come under some interesting questioning.

1. Acetaminophen Reduces “Social Pain”

The first study to test the psychological effects of acetaminophen drew inspiration from prior research on the connection between physical pain and social pain. Briefly, a bunch of studies have suggested that our brains treat physical sensations of pain (“I stubbed my toe!”) similarly to social varieties of pain (“She broke up with me!”). After all, we tend to use pretty physical language to talk about painful emotional experiences: “You hurt my feelings!” or “She broke my heart!”

So if feeling left out and getting a headache are the same as far as your brain’s pain center is concerned, shouldn’t a pain killer also kill the unpleasant emotional pain? That’s what a couple studies by Nathan DeWall and his colleagues showed.

In one of their studies, they asked a bunch of people to keep a daily log of how much they experienced having their feelings hurt over a three-week period. All of these people were also taking a pill each day. Half were taking acetaminophen and half were taking a placebo, but they didn’t know which one they were taking.

Over those three weeks, the people taking acetaminophen started feeling less emotional pain every day, but the people taking the placebo didn’t show any evidence of change. The take-home point here was that this simple pain killer was capable of reducing feelings of social pain over time.

2. Acetaminophen Makes Death Less Terrifying

There’s a big theory in social psychology called Terror Management Theory, and the main idea is that it’s really uncomfortable to contemplate our own mortality. So if we have to think about death, we engage in a bunch of cognitive biases that helps bring a sense of order back into the world (at least as far as we can convince ourselves).

For instance, when researchers ask people to think about death, those people then feel motivated to punish people who violate a common moral code. The overwhelmingly common way in which researchers study this is to ask people how severely they would punish someone who was caught engaging in prostitution. By punishing these “moral offenders,” people can feel more connected to an enduring culture and value system that will outlast their own short lives.

Uplifting, right!?

What if there was a little pill that could ease this existential dread? Tylenol to the rescue again. People who had taken a dose of acetaminophen were less affected by contemplating death, even though people who had taken a placebo showed the classic effects of thinking about death.

3. Acetaminophen Reduces Empathy

Just a couple weeks ago, a new set of acetaminophen studies hit the presses. These researchers figured, “acetaminophen reduces one’s own physical and social pain…would it reduce our perceptions of another person’s pain?”

Psychologists often define empathy as our proneness to experience another person’s sensations as our own. So if someone is in pain, the empathic response is to also feel a version of that pain. In fact, evidence from neuroimaging studies has shown that when people see another person in pain, their brains react as if they themselves were in pain.

So based on what we’ve seen already, maybe the pain relieving properties of acetaminophen could reduce empathy, too, by reducing the vicarious pain experience. These researchers gave a whole bunch of participants a collection of tasks that would elicit empathy.

For example, they gave them short stories about another person who was experiencing physical pain (e.g., getting his finger slammed in the door) or social pain (e.g., overhearing other people say that they disliked him). After reading the stories, the participants would indicate how much pain the character experienced and how much empathy they had for him. Another activity involved witnessing someone getting ignored while playing a group game–a commonly studied case of social rejection.

The results of the study showed that, across these various empathy-inducing activities, people who had taken a dose of acetaminophen showed less empathy than people who had taken a placebo.

4. Acetaminophen Makes Good Things Less Good, Too

You might have noticed a theme in the above points. Acetaminophen seems to make bad things less bad. It makes pain less painful. It makes being excluded less traumatic. It makes death less terrifying. It makes us experience less pain on behalf of others. Other studies have only added to this list: acetaminophen makes surrealistic art less disturbing and reduces the “pain” of making difficult decisions.

But what about good stuff? Does acetaminophen affect any of that, too? One set of studies tested this question to see whether acetaminophen was really about making bad things less unpleasant or whether it was instead about making our reactions to things less extreme–good or bad.

Participants in these studies saw a bunch of emotionally evocative pictures. Some were really pleasant and some were really unpleasant. As you might expect, people who took a dose of acetaminophen saw the negative pictures as being less unpleasant than people who took a placebo. So far, we’ve got another case of bad stuff getting less unpleasant under Tylenol.

More interestingly, though, is that people who had taken acetaminophen also saw the positive pictures as less pleasant than people who took placebo. That is, what acetaminophen seems to be doing is affecting our evaluations of the world in front of us…whether it’s a negative or positive evaluation.

Consistent with this idea, some more recent research using EEG has shown that acetaminophen affects basic evaluation processes.

Toward a New Understanding of Acetaminophen

It’s pretty clear that acetaminophen–and the many drugs this chemical can be found in–is doing something interesting in our brains that goes beyond simple pain killing. What remains to be seen, though, is exactly why it’s having these effects. When this drug gets into our bodies, what happens? What process does it unlock that has implications for our social and emotional lives?

Another interesting question that this research raises is: why acetaminophen? Why not other popular pain killers like ibuprofen? This body of research is still pretty new, and time will tell whether these effects are specific to acetaminophen or whether all pain killers have these influences.

Finally, it’s worth pointing out that these results shouldn’t necessarily make you rush to CVS to stock up on off-brand Tylenol. People often hear this research and think, “I’ll just pop a Tylenol the next time someone hurts my feelings!”

Not so fast. This research has been really interesting for researchers as they get a better sense of the complicated relationship between neurochemistry and our psychological experience. The evidence is less clear on the everyday practical applications of these findings. Plus, acetaminophen is pretty darn dangerous. A report by ProPublica warns: nearly 1,500 Americans have died in the last decade following an overdose of acetaminophen. It’s a drug that can tax the liver and shouldn’t be taken lightly. Let ye be warned!

In full disclosure, I was on the research team for one of the papers referenced in this post, and friends of mine were involved in others!

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