During an announcment Monday, the US president repeatedly advised people, “Don’t take Tylenol,” but scientists say that strong evidence between the medication and autism is lacking.
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 today, the US Food and Drug Administration (FDA) announced that it would slap a warning label on the drug, citing a “possible association” between autism in children and the use of acetaminophen, also called Tylenol in the United States, during pregnancy.
US President Donald Trump, however, was not as nuanced in his language: “Don’t take Tylenol,” he said repeatedly in a widely anticipated announcement about autism. “Fight like hell not to take it,” he said.
Autistic people show differences in social communication and interaction, and, over the past few decades, the reported prevalence of the developmental condition has risen in some countries. But many researchers who study autism caution that there are insufficient data to link it with acetaminophen, and that focusing on this is merely a distraction.Autism is on the rise: what’s really behind the increase?
“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 charity for autism research and campaigning in London, who is autistic. “At the heart of this is people trying to look for simple answers to complex problems.”
At today’s announcement, US health secretary Robert F. Kennedy Jr acknowledged that autism has many possible causes. FDA commissioner Martin Makary noted that, in some cases, insufficient transport of the nutrient folate into the brain has been linked with traits common in autism. The FDA announced today that it would initiate approval of a form of folate, called leucovorin, for people with low levels of the vitamin in the fluid surrounding the brain and spinal cord.
But Kennedy, a long-time anti-vaccine advocate, and Trump focused their attention on two other factors that they said could be linked to autism: acetaminophen and vaccines. Decades of research have not uncovered a reproducible link between vaccines and autism.
“The evidence does not support a causal link between acetaminophen or vaccines and autism,” says Sura Alwan, a clinical teratologist at the University of British Columbia in Vancouver, Canada, and executive director of the PEAR-Net Society, a non-profit organization in Vancouver advocating for maternal–fetal health and research. “Suggesting otherwise may fuel misinformation and undermine confidence in safe treatments and immunizations.”
Here, Nature examines the evidence for a link between acetaminophen, which is used to treat fever as well as pain, and autism.
How strong are the data connecting autism and acetaminophen during pregnancy?
Scientists say that the most-robust research has found no link. “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 in 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 that researchers rely on self-reports, which can be unreliable.
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Confounding factors are an even bigger problem. Many pregnant people who take paracetamol have a health problem, such as an infection or underlying condition. Any apparent link between acetaminophen and autism might therefore be explained by these other health factors, rather than the drug itself. Scientists try to adjust for this in their studies, but this is “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 from 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 with 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), in which one had been exposed to acetaminophen and one had not. Siblings share half of their genome, a similar upbringing and maternal health, so differences in autism are more likely to be due to the drug. Using this method, the researchers found no association between acetaminophen and autism — which supports the idea that links found in other studies could be explained by confounding factors.
A large, high-quality study2 from Japan of more than 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 last month 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, a social and developmental psychologist at Durham University, UK, said in comments to the Science Media Centre, a press office in London.
“We believe independent, sound science clearly shows that taking acetaminophen does not cause autism,” says a spokesperson for Tylenol’s manufacturer, Kenvue in Summit, New Jersey.
What’s the harm in warning pregnant people not to take the medication?
Scientists say that medications for relieving pain and fever during pregnancy are scarce, and that acetaminophen has one of the longest and safest track records. Advising pregnant women against taking it would be “hugely dangerous”, says Flusberg. Such advice is “bound to increase fear in pregnant women at a time when they truly don’t need to, and it is absolutely not grounded in the scientific findings”.
“Pain relief for pregnant women is woefully lacking,” Botha said. “Paracetamol is a much safer pain-relief option during pregnancy than basically any other alternative.”
Linking a use of medication during pregnancy to the child’s autism could also have negative effects on parents, researchers say. “We risk placing blame on mothers and causing more stress, self-blame and stigma, despite having no evidence to support such claims,” Alvquist says.
If acetaminophen use is not behind the rise in autism, what is?
Researchers say that the vast majority of the increase in autism prevalence over the past couple of decades can be explained by an increase in diagnoses, rather than a real growth in underlying symptoms. The diagnostic criteria have changed over the years so that they apply to more people — including adults, as well as children — and diagnoses have grown as clinical professionals have changed how they interpret and apply the criteria.
What’s more, specialists say, more people are seeking and receiving diagnoses as awareness of autism has grown. Sometimes parents pursue a diagnosis because it can help children to access education or health support, and more adults are receiving diagnoses, too.