Acetaminophen, known by the brand names Tylenol and Panadol, is the most widely used drug ingredient in the U.S., taken by more than 50 million Americans every week.1 Most don’t think twice about popping a couple of Tylenol tablets to take the edge off a headache or other minor aches and pains, believing it to be a relatively benign over-the-counter medication choice.
Even acetaminophen comes with risks, however. Those linked to liver damage are well known, but it’s now emerging that acetaminophen has other unintended effects in your body — effects that may influence your behavior, emotions and psychological processes. Taken together, if you don’t have to use acetaminophen, don’t — it’s best to avoid using this drug unless absolutely necessary.
Acetaminophen Increases Risk Taking
Acetaminophen, which is found in over 600 medicines, is used by 23% of the U.S. population weekly,2 mostly for its pain- and fever-reducing effects. But along with blunting your pain, it may also be dampening your response to risks, such that you become more likely to take them while using the drug.
Researchers from The Ohio State University recruited 189 college students to take part in the study. They were given either 1,000 milligrams (mg) of acetaminophen or a placebo, then, once the drug took effect, they were asked to rate various activities based on risk on a scale of 1 to 7.
Those who took acetaminophen rated the activities, which included things like walking home alone at night in an unsafe area or bungee jumping, as less risky than those who took the placebo. In another study by the same researchers, undergraduate students took part in a test to measure risk-taking behavior.3
The study involved clicking a button to inflate a balloon on a computer. As it inflated, they were rewarded with money, but if it got too big and burst, they lost it all. Students who took acetaminophen were more likely to keep pumping the balloon and had more balloons burst than students not taking the drug.
“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,” study co-author Baldin Way said in a news release. “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.”4
Taking more risks on the laboratory test has been linked to increased risk-taking outside of the lab, including driving without a seatbelt, using drugs and alcohol and stealing. This is what has the researchers concerned, especially considering how widespread acetaminophen usage is.
“Acetaminophen seems to make people feel less negative emotion when they consider risky activities — they just don’t feel as scared,” Way said. “With nearly 25 percent of the population in the U.S. taking acetaminophen each week, reduced risk perceptions and increased risk-taking could have important effects on society.”5
Acetaminophen Blunts Positive and Negative Emotions
If you take acetaminophen, you expect it to dull your physical pain, but it may also blunt your emotions, both positive and negative. A series of studies, conducted by Way and colleagues, involved showing college students 40 photographs designed to elicit positive, neutral or negative emotions.6 The students were given 1,000 mg of acetaminophen or a placebo 60 minutes prior to viewing the photos.
The students were asked to rate the photos on a scale of -5 (extremely negative) to +5 (extremely positive), as well as rate how much emotion the photo made them feel. Those who took acetaminophen rated the photos as less extreme on either end of the spectrum, and also had more neutral emotional reactions.
“People who took acetaminophen didn’t feel the same highs or lows as did the people who took placebos,” Way said in a news release.7 They then conducted a similar study asking people to evaluate not only the emotional content of photos, but also how much of the color blue it contained. They were trying to determine if acetaminophen affected perceptions that weren’t emotional in nature.
Again, the participants who took acetaminophen had emotional reactions that were significantly blunted, but the judgments of blue color content were similar among everyone. This suggests acetaminophen affects emotional evaluations but not magnitude judgments, such as color content.8
Acetaminophen Is an ‘Empathy Killer’
Acetaminophen is not only a painkiller but also an “empathy killer,” Way and colleagues wrote in a 2016 study published in Social Cognitive and Affective Neuroscience.9Empathy, the ability to put yourself in someone else’s shoes and understand their feelings and point of view, is a character trait that benefits society and individuals in multiple ways.
Those who feel empathy for others’ pain and suffering may trigger prosocial actions, for instance, or curb aggressive behaviors. It’s also known that when people observe others experiencing pain, brain regions are activated that also light up in response to our own pain.10 This suggests empathy for pain may share similar neural and psychological processes as the experience of physical pain.
Again, Way and colleagues conducted a series of studies to compare subjects’ responses to others’ physical or social pain. After receiving acetaminophen or a placebo, they read scenarios about another’s pain, watched ostracism in the lab or witnessed other participants being exposed to painful noise blasts.
The acetaminophen users had significantly fewer empathic responses compared to those who took a placebo. The researchers explained:11
“As hypothesized, acetaminophen reduced empathy in response to others’ pain. Acetaminophen also reduced the unpleasantness of noise blasts delivered to the participant, which mediated acetaminophen's effects on empathy.
Together, these findings suggest that the physical painkiller acetaminophen reduces empathy for pain and provide a new perspective on the neurochemical bases of empathy. Because empathy regulates prosocial and antisocial behavior, these drug-induced reductions in empathy raise concerns about the broader social side effects of acetaminophen …”
Taking Acetaminophen Reduces Pain From Social Rejection
The pain caused by social rejection is another area where acetaminophen unexpectedly interferes. Those who took acetaminophen daily for three weeks reported less social pain on a daily basis compared to those who took a placebo.12
Further, when the researchers used functional magnetic resonance imaging to measure brain activity in the participants, the drug reduced neural responses to social rejection in areas previously linked to the distress of social pain and physical pain.
“Acetaminophen reduces behavioral and neural responses associated with the pain of social rejection, demonstrating substantial overlap between social and physical pain,” the researchers noted.13 Indeed, the pain of social rejection can feel like a literal painful blow, but the problem with taking acetaminophen to blunt it is that positive emotions are also affected, meaning chronic users may have a dulled existence.
When Way and colleagues again gave 1,000 mg of acetaminophen or placebo to subjects, then measured their response to positive empathy, these positive feelings were blunted; those taking acetaminophen did not experience the same uplifting feelings as others did when reading about others’ positive experiences.14
“Results showed that acetaminophen reduced personal pleasure and other-directed empathic feelings in response to these scenarios,” Way and colleagues wrote, adding that this also has societal implications since positive empathy is related to prosocial behavior.
Cognitive Function Also Affected
When acetaminophen affects your brain’s responses to social rejection, empathy and more, it also extends to other cognitive processes, possibly making them less effective. In another trial, participants who took either acetaminophen or a placebo performed a test to gauge decision-making abilities.
They had to click a button when the letter F appeared on a computer screen but not hit the button when an E was shown. Those who took acetaminophen performed worse on the test, suggesting the drug may lead to greater errors or flaws in decision making, and may also inhibit broader evaluative processes in the brain.15
Lead author Dan Randles, a postdoctoral fellow in the psychology department at University of Toronto, said in an interview with Forbes:16
“… [A]cetaminophen 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.”
Acetaminophen Is Risky During Pregnancy
After long being recommended as a safe pain reliever during pregnancy, it was revealed in 2014 that acetaminophen is in fact a hormone disruptor,17 casting doubts on its safe use during pregnancy.
According to that 2014 study, use of acetaminophen during pregnancy was associated with a 37% increased risk of their child being diagnosed with hyperkinetic disorder, a severe form of attention deficit hyperactivity disorder (ADHD).
Their children were also up to 30% more likely to be prescribed ADHD medication by the time they were 7 years old.18 A study published in JAMA Psychiatry in 2019 further strengthened the link between acetaminophen use and ADHD, while also noting an increased risk for autism spectrum disorder (ASD).19 Aside from a higher risk of neurodevelopmental problems, studies have also shown:
- Use of acetaminophen during pregnancy may increase your risk of pre-eclampsia and thromboembolic diseases20
- Taking the drug for more than four weeks during pregnancy, especially during the first and second trimester, moderately increases the risk of undescended testicles in boys21
- Using acetaminophen in the third trimester increases your risk of preterm birth22
Liver Damage Is a Major Problem With Acetaminophen Use
Yet another reason to be extremely cautious with regard to acetaminophen is its negative effects on your liver. Acetaminophen is the top cause of acute liver failure in the U.S. It can even be toxic to your liver at recommended doses when taken daily for just a couple of weeks.23
Part of the reason for the risk is that acetaminophen's recommended dose and the amount of the drug that causes an overdose are very close. There is not much margin of safety, and because acetaminophen is found in so many over-the-counter medications, it’s easy to double- or triple-up without even realizing it.
Even taking just a little more acetaminophen than the recommended dose over a few days or weeks (referred to as “staggered overdosing”) is dangerous, and can be deadlier than one large overdose.24 There are other risks to acetaminophen that haven’t been covered here, including potentially fatal skin reactions.
California state regulators are even considering adding acetaminophen to the list of carcinogens covered by Proposition 6525 because it’s related to phenacetin, an over-the-counter painkiller banned by the U.S. Food and Drug Administration in 1983 because of links to cancer.
Considering its many risks, I don’t recommend using acetaminophen for minor aches and pains. Instead, try one of the many natural pain relief options available that can provide relief without drugs.