When Zeyan Liew joined a Danish team that was studying a large, national database of mothers and their children in 2011, he was interested in understanding brain development in children. “ADHD [attention deficit hyperactivity disorder] and autism were the two fastest-growing neurological and behavioural disorders at that time,” he recalls. “We and other scientists were not sure what was driving these increasing trends.”
It was difficult to tease out, Liew says, because greater parental awareness and better diagnosis had a role in the rise in ADHD cases. “The question was, are there real increases?” says Liew, now an epidemiologist at the Yale School of Public Health in New Haven, Connecticut.
Genetic heritability underlies many cases of ADHD, but genetics cannot explain why the number is increasing — more than 20-fold in recent decades, according to some estimates1.
Nature Outlook: ADHD
The team’s data showed that more than half of mothers had taken a particular drug during pregnancy, often at high doses and for long durations, making it a suspect.
That drug was N-acetyl-para-aminophenol, known as paracetamol in Europe, and as acetaminophen in the United States, Japan and many other countries. It is marketed under various brand names, including Panadol and Tylenol, and it is a component of more than 600 products for pain and fever relief2. It has long been considered one of the safest drugs to take during pregnancy, avoiding the serious risks to the fetus posed by the use of non-steroidal anti-inflammatory drugs, such as aspirin and ibuprofen, and opioids. Worldwide, more than half of women take it during pregnancy.
But a growing body of evidence now shows increased rates of ADHD and other neurodevelopmental disorders, including autism spectrum disorder, in children whose mothers took the drug during pregnancy. The potential link had a moment in the public spotlight in September 2025, when US health secretary Robert F. Kennedy Jr and President Donald Trump pointed to paracetamol as a cause of autism and urged pregnant women to avoid the drug altogether.
The evidence is inconsistent, however. Some studies show a stronger association than others, and some have found no increased risk at all. “The science between prenatal acetaminophen exposure and specifically autism is not settled, and it is premature to declare this is a proven cause,” says Liew. “We certainly should not make people fear using a treatment when it is needed and when there is no alternative.”
Many women do not even think of paracetamol as a drug, says David M. Kristensen, a molecular physiologist at Roskilde University and Copenhagen University Hospital in Denmark. Kristensen is one of the authors of a consensus statement calling for better awareness of links between paracetamol and various neurodevelopmental, reproductive and urogenital disorders2. “What was fuelling our concern,” says Kristensen, “was a lot of women not realizing that this is a real medication with real side effects.”
Cause for concern
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