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Experts issue warning after world's most common painkiller has a bizarre and unexpected side effect READ MORE: Common pills taken by MILLIONS blamed for death of a 32 year-old By JOHN ELY DEPUTY HEALTH EDITOR FOR MAILONLINE Published: 04:34 EDT, 5 April 2025 | Updated: 04:47 EDT, 5 April 2025 e-mail View comments An over-the-counter painkiller regularly taken by millions of Britons each year could trigger bizarre personality changes, scientists have warned. Experts have discovered that paracetamol, known as acetaminophen and sold as Tylenol in the US, triggers risk-taking behaviour in some people. In experiments involving almost 550 people, those given paracetamol were far less likely to rate as risky activities like passing off someone else's work as their own.
They also felt more comfortable with the idea of driving a car without wearing a seatbelt than those given a placebo, or dummy tablet. And in another experiment, in which participants played a computer game where they inflated balloons for cash, those on paracetamol far more likely to keep playing and burst the balloon—losing all their winnings—than those given a dummy pill. These experiments are said to predict if a person might participate in more serious risky behaviours, such as high risk sexual encounters, dangerous driving, drug and alcohol use and shoplifting.
Ohio State University neuroscientist Professor Baldwin Way, author of the study, said: 'Acetaminophen seems to make people feel less negative emotion when they consider risky activities—they just don't feel as scared.' He added that the implications are potentially huge given how widely the drugs are taken. Paracetamol, known as acetaminophen in the US, is one of the most common drugs taken across the world and is a key ingredient in medications like Panadol or Tylenol 'With nearly 25 per cent of the population in the US taking acetaminophen each week, reduced risk perceptions and increased risk-taking could have important effects on society,' he said.
The study itself notes that many patients in hospital have paracetamol in their system when asked to make 'potentially life-changing' decisions such as undergoing risky surgery or before performing potentially dangerous tasks like driving. British studies also show paracetamol—available for as little as 2p per pill at some supermarkets—is a frequently used painkiller. An estimated 200million packets are sold over the counter each year in the UK, equivalent to every Briton using three packets per year or about 70 tablets.
NHS backed data also suggests 1.6million paracetamol prescriptions were dished out by GPs in England last year, to the cost of almost £70million to the taxpayer. The health service insists paracetamol is safe for the vast majority of patients provided it's taken at the correct dosage.
Taking too much at once can cause liver damage and research has suggested frequent use could be dangerous. Read More Taking statins could slash dementia risk - even if you don't have high cholesterol One study in 2022 found that popping a paracetamol every day could raise the risk of a deadly heart attack or stroke by about a fifth. Another study that same year found that certain formulations of the drug could contain more salt per dose than a McDonald's Big Mac .
In Professor Way's study, researchers tested the impact of paracetamol on risk taking on 545 university students across three experiments. Before the tests half the group were given either 1,000mg of paracetamol, equivalent to about double the usual dose for adults, or a placebo. Publishing the findings in the journal Social Cognitive and Affective Neuroscience , the researchers theorised the increased risk taking could be due to the painkiller reducing anxiety about the future.
Referencing the balloon bust experiment they said: 'It may be that as the balloon increases in size, those on placebo feel increasing amounts of anxiety about a potential burst,' they explained. 'When the anxiety becomes too much, they end the trial.' 'Acetaminophen may reduce this anxiety, thus leading to greater risk-taking'.
While the researchers observed the impact paracetamol had on risk-taking, they said the biological mechanism of how the drug was doing this remained unclear and an area for future research. NHS Share or comment on this article: Experts issue warning after world's most common painkiller has a bizarre and unexpected side effect e-mail Add comment Comments 0 Share what you think No comments have so far been submitted. Why not be the first to send us your thoughts, or debate this issue live on our message boards.
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