Scientists find no link between Tylenol and autism, again, after Trump warning - Ars Technica

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Another large study has found no link between autism and Tylenol use during pregnancy, refuting claims by President Trump and anti-vaccine Health Secretary Robert F. Kennedy Jr.

In September, Trump and Kennedy held a press conference in which they stated without clear evidence that the common fever and pain reducer acetaminophen—sold as Tylenol in the US and also known as paracetamol—causes autism in children if taken during pregnancy. Trump repeatedly warned pregnant people not to take Tylenol and instead “tough it out” with fever and/or pain.

Medical organizations decried Trump’s message, emphasizing that acetaminophen is a safe pain and fever reliever during pregnancy and that untreated fever during pregnancy is known to increase the risk of autism in babies as well as other conditions, including miscarriage, birth defects, and premature birth. Still, the president’s warning was effective. Texas sued the maker of Tylenol over the alleged connection. And a study in The Lancet in March found that use of acetaminophen in pregnant patients in emergency departments fell by 10 percent after Trump’s press conference.

In the new study published in JAMA Internal Medicine, researchers analyzed electronic health records from 2001 to 2023 for more than 700,000 pairs of mothers and children in Hong Kong. Of those pairs, about 43 percent of children had exposure to acetaminophen in utero.

Sibling-matched design

The researchers then performed a sibling-matched analysis, comparing autism and ADHD cases among siblings, some of whom were exposed to acetaminophen in utero and some who weren’t. This study design helps account for unmeasured family factors that influence the likelihood of the conditions, particularly genetics and shared environmental conditions. The autism analysis included over 124,000 sibling-matched children, and an analysis of attention-deficit/hyperactivity disorder (ADHD) included a cohort of over 97,000 sibling-matched children.

The researchers saw no link between prenatal acetaminophen use and either condition. It didn’t matter what dosage of acetaminophen was taken, when it was taken during the pregnancy (which trimester), how often it was taken, or how old the mother was at the time. There was simply no link between acetaminophen and autism or ADHD.

Interestingly, there was a link when the researchers dropped the sibling-matched design and instead compared acetaminophen-exposed with unexposed children, which is a finding that has come up in other studies. But when the researchers performed a “negative control” analysis and compared children whose mothers had taken acetaminophen before ever getting pregnant or after they had given birth compared to mothers who didn’t use the painkiller, they also saw an association—one that is “biologically implausible.”

“Collectively, these findings suggest that the positive signal observed in both conventional and negative control analyses reflect residual familial confounding, rather than a true pharmacologic effect of prenatal paracetamol exposure,” the researchers concluded.

The finding of no association between acetaminophen use in pregnancy and neurodevelopmental conditions in children was also found in large sibling-matched studies in Sweden in 2024 and Japan in 2025.

Beth Mole

Senior Health Reporter

Beth Mole

Senior Health Reporter

Beth is Ars Technica’s Senior Health Reporter. Beth has a Ph.D. in microbiology from the University of North Carolina at Chapel Hill and attended the Science Communication program at the University of California, Santa Cruz. She specializes in covering infectious diseases, public health, and microbes.

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