Pregnant people have long relied on paracetamol for pain and fever. Credit: BSIP/Universal Images Group/Getty
The painkiller acetaminophen or paracetamol is one of the most widely taken drugs during pregnancy, used by roughly half of all pregnant people worldwide. But US president Donald Trump said Sunday that he thinks the medication is “a very big factor” in autism. And both the Washington Post and Politico report that an announcement from the Trump administration today will raise concerns about a link between autism and use of Tylenol by pregnant people. The details of the announcement are not yet clear.
Autistic people show differences in social communication and interaction, and reported prevalence of the condition has risen in some countries in recent decades. But many researchers who study autism caution that there is insufficient data to link autism and acetaminophen and that focusing on such a link is no more than a distraction.
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“There is no definitive evidence to suggest that paracetamol use in mothers is a cause of autism, and when you see any associations, they are very, very small,” says James Cusack, chief executive of Autistica, a UK autism research and campaigning charity in London, who is autistic. “At the heart of this is people trying to look for simple answers to complex problems.”
In a press briefing ahead of the announcement, White House press secretary Karoline Leavitt declined to provide specifics about the administration’s conclusions. “This will be a powerful display of how the entire Trump administration is committed to addressing root causes of chronic conditions and diseases,” she said. When asked by a reporter whether an announcement linking acetaminophen and autism might confuse pregnant women, Leavitt told reporters not to jump to conclusions based on media reports that the White House had not yet confirmed.
Here Nature examines the evidence for a link between the medication, which is used to treat fever as well as pain, and autism.
How strong are the data connecting autism and acetaminophen?
Scientists say that the most robust research does not link autism and acetaminophen use in pregnancy. “The better controlled studies are less likely to find even a small risk,” says Helen Tager-Flusberg, a psychologist who studies autism at Boston University, Massachusetts, “And even then, what we’re talking about is a minor association. … We do not think that taking acetaminophen is in any way contributing to actually causing autism.”
Working out whether there is a link between the drug and autism is difficult, says Viktor Ahlqvist, an epidemiologist at the Karolinska Institute in Stockholm and co-author of what might be the biggest study1 on the link. The medication is available over the counter, so a lot of usage is not recorded in medical databases. This means researchers rely on self-reports, which can be unreliable.
Confounding factors are an even bigger problem. Women who take paracetamol in pregnancy are usually in poorer health than those who don’t, perhaps because they had an infection or an underlying condition. Any apparent link between acetaminophen and autism might therefore be explained by these other health factors rather than the drug itself. Although scientists try to adjust for such confounders in their studies, such adjustments are “rarely sufficient,” Ahlqvist says. This is one reason why studies looking for a link have produced conflicting results.
The study led by Ahlqvist harnessed data on nearly 2.5 million children born in Sweden between 1995 and 2019 and — from the country’s extensive health records — data on acetaminophen prescriptions during pregnancy and on self-reported use collected by midwives, as well as whether children later received autism diagnoses.
The study showed that around 1.42% of children exposed to acetaminophen during pregnancy were autistic, compared to 1.33% of children who were not exposed ─ a “very small” difference, says Ahlqvist.
The team also compared pairs of siblings (born to the same mother), one of whom had been exposed to acetaminophen and one who had not. Siblings share half of their genome, and share a similar upbringing and mother’s background health, so any detected difference in autism between siblings is more likely to be due to the drug. The researchers found no association between acetaminophen and autism using this method — which supports the idea that links found in other studies were really explained by confounding factors.
Another large, high-quality study2 from Japan including over 200,000 children — also using sibling comparisons and published this year — found no link between acetaminophen use in pregnancy and autism.
Are there any studies that do link the medication and autism?
A review3 of studies published in August in the journal Environmental Health concluded that there is an association. But researchers interviewed by Nature point instead to the contrasting results of a review4 of high-quality studies on the topic. That review, published in February, concluded that “in utero exposure to acetaminophen is unlikely to confer a clinically important increased risk” of autism spectrum disorder.
“There is no robust evidence or convincing studies to suggest there is any causal relationship and any conclusions being drawn to the contrary are often motivated, under-evidenced, and unsupported by the most robust methods ,” Monique Botha, associate professor in social and developmental psychology at Durham University, UK, said in comments to the Science Media Centre, a UK press office.
“We believe independent, sound science clearly shows that taking acetaminophen does not cause autism,” says a spokesperson for Tylenol’s manufacturer, Kenvue Inc. in Summit, New Jersey.
