At a White House event Monday, Trump linked acetaminophen, the active ingredient in Tylenol, to autism and encouraged women to tough out fevers. The remarks, made alongside health secretary Robert F. Kennedy Jr. — a longtime critic of mainstream medicine — rattled doctors and drugmakers. 

Mady Hornig, a New York physician-scientist who has studied pregnancy-related risk factors for autism and attention deficit hyperactivity disorder for 25 years, said the White House’s message misrepresents the science around acetaminophen, which is also known as paracetamol in Europe and elsewhere.

“It seemed like they had indicated that there was evidence that prolonging a fever is a good thing,” Hornig, a visiting scientist at the Feinstein Institutes for Medical Research, Northwell Health, said in an interview. “It’s astonishing misinformation.” 

Trump and Kennedy have both sought to challenge health guidance and practices, sometimes relying on cherry-picked evidence. The US leader also has a record of promoting unfounded medical theories.

The American College of Obstetricians and Gynecologists called the latest advice on acetaminophen “irresponsible,” while the American Academy of Pediatrics also said misrepresenting science does a “disservice” to autistic people. The UK’s Medicines and Healthcare Products Regulatory Agency said there’s no evidence that paracetamol causes autism and said it remains safe during pregnancy. 

Genetic Risk 

Hornig’s research, based on the Norwegian Mother, Father and Child Cohort Study of over 100,000 families, found that moderate or high fevers in pregnancy were linked to elevated autism risk, especially in the second trimester. 

“We found that there was about a 40% increased risk of autism without acetaminophen,” she said. “That went down substantially with the use of acetaminophen.”

She stressed that fever itself, not a single drug, is a key factor. 

“It’s clear that unmitigated fever, particularly where it is of a moderate level or higher, is something that has an impact on offspring to increase risk of autism,” she said. “To allow women to have even a modest fever during pregnancy, which in and of itself can potentially cause damage and is associated in many studies with risk, is very worrisome.”

In preliminary, unpublished work, Hornig’s team also saw hints that acetaminophen taken for pain may carry different risks. “There seems to be some pattern that suggested that for pain, it may not be the drug to use,” she added, though she cautioned the findings need more study.

A small number of women reported using ibuprofen for fever during pregnancy. None of their children developed autism, though Hornig stressed the numbers were too small to draw conclusions.

The findings underscore what scientists have long said: autism doesn’t have a single cause. Genetics, timing and environment all interact, Hornig said, citing factors such as parental age gaps, exposure to wildfire smoke and heavy metals, seasonal immune shifts and infections that trigger fever.

“The idea that it’s going to be a singular cause is really kind of foolhardy, and it doesn’t go along with the things that we know,” she said.

Hornig also urged more precision in research. Common genetic differences in enzymes that help break down acetaminophen may influence how safely a pregnant woman can metabolize the drug. Some labs are testing newborns’ meconium for toxic byproducts of acetaminophen metabolism — a potential biomarker that could guide safer choices in the future.

“Our future generations deserve a personalized approach that looks at genetic risk, environmental exposures, and safer alternatives,” she said. 

For now, she said, context matters. Acetaminophen remains widely recommended because aspirin carries a risk of Reye’s syndrome and ibuprofen isn’t considered safe later in pregnancy. But Hornig warned that discouraging treatment altogether — especially with respiratory viruses like flu and Covid-19 still circulating — could leave women vulnerable.

Vaccination before and during pregnancy, when indicated, remains one of the best safeguards against infections that trigger fever, she added.