World's Most Common Pain Relief Drug May Induce Risky Behavior, Study Finds

One of the most consumed drugs in the US – and the most commonly taken analgesic worldwide – may do a lot more than simply take the edge off your headache.

Acetaminophen, also known as paracetamol and sold widely under the brand names Tylenol and Panadol, may also increase risk-taking, according to a study from 2020 that measured changes in people's behavior when under the influence of the common over-the-counter medication.

"Acetaminophen seems to make people feel less negative emotion when they consider risky activities – they just don't feel as scared," explained neuroscientist Baldwin Way from The Ohio State University when the findings were published.

"With nearly 25 percent of the population in the US taking acetaminophen each week, reduced risk perceptions and increased risk-taking could have important effects on society."

The findings add to a growing body of research suggesting that acetaminophen's effects on pain reduction also extend to various psychological processes, lowering people's receptivity to hurt feelings, experiencing reduced empathy, and even blunting cognitive functions.

In a similar way, the research suggests people's affective ability to perceive and evaluate risks may potentially be altered or impaired when they take acetaminophen.

While the effects might be slight – and should be considered hypothetical for now – they're worth noting, given acetaminophen is the most common drug ingredient in America, found in over 600 different kinds of over-the-counter and prescription medicines.

In a series of experiments involving over 500 university students as participants, Way and his team measured how a single 1,000 mg dose of acetaminophen (the recommended maximum adult single dosage) randomly assigned to participants affected their risk-taking behavior, compared against placebos randomly given to a control group.

In each of the experiments, participants had to pump up an un-inflated balloon on a computer screen, with each single pump earning imaginary money.

Their instructions were to earn as much imaginary money as possible by pumping the balloon as much as possible, but to make sure not to pop the balloon, in which case they would lose the money.

The results showed that the students who took acetaminophen engaged in significantly more risk-taking during the exercise, relative to the more cautious and conservative placebo group. On the whole, those on acetaminophen pumped (and burst) their balloons more than the controls.

"If you're risk-averse, you may pump a few times and then decide to cash out because you don't want the balloon to burst and lose your money," Way said.

"But for those who are on acetaminophen, as the balloon gets bigger, we believe they have less anxiety and less negative emotion about how big the balloon is getting and the possibility of it bursting."

In addition to the balloon simulation, participants also filled out surveys during two of the experiments, rating the level of risk they perceived in various hypothetical scenarios, such as betting a day's income on a sporting event, bungee jumping off a tall bridge, or driving a car without a seatbelt.

In one of the surveys, acetaminophen consumption did appear to reduce perceived risk compared to the control group, although in another similar survey, the same effect wasn't observed.

While an experiment like this doesn't necessarily reflect how acetaminophen might affect people in real-life scenarios, based on an average of results across the various tests, the team concluded that there is a significant relationship between taking acetaminophen and choosing more risk, even if the observed effect appears slight.

That said, the researchers acknowledged the drug's apparent effects on risk-taking behavior could also be interpreted via other kinds of psychological processes, such as reduced anxiety, perhaps.

"It may be that as the balloon increases in size, those on placebo feel increasing amounts of anxiety about a potential burst," the researchers explained.

"When the anxiety becomes too much, they end the trial. Acetaminophen may reduce this anxiety, thus leading to greater risk taking."

Exploring such psychological alternative explanations for this phenomenon – as well as investigating the biological mechanisms responsible for acetaminophen's effects on people's choices in situations like this – should be addressed in future research, the team said.

Despite the potential impact of acetaminophen's effect on people's risk perception, the drug nonetheless remains one of the most important and highly used medications in the world, considered an essential medicine by the World Health Organization, even if other questions linger.

"We really need more research on the effects of acetaminophen and other over-the-counter drugs on the choices and risks we take," Way said.

The findings were reported in Social Cognitive and Affective Neuroscience.

An earlier version of this article was published in September 2020.

A subsequent commentary published in 2021 highlighted some criticisms of the original study and its interpretation in the media.

This article has been updated to better reflect the hypothetical nature of the study and its findings. For further information, see here.