Scientists hit out at Trump’s claim of Tylenol-autism link, say fever a bigger danger in pregnancy

US President Donald Trump’s call for pregnant women to avoid Tylenol is drawing sharp criticism from researchers who say the advice ignores decades of evidence and could endanger mothers and babies.

At a White House event on Sept 22, Mr Trump

linked acetaminophen, the active ingredient in Tylenol, to autism

and encouraged women to tough out fevers. The active ingredient is known as paracetamol in Singapore.

The remarks, made alongside health secretary Robert F. Kennedy Jr – a long-time critic of mainstream medicine – rattled doctors and drugmakers. 

Dr 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 science.

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

Mr Trump and Mr 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 Gynaecologists called the latest advice on acetaminophen “irresponsible”, while the American Academy of Paediatrics said misrepresenting science does a “disservice” to autistic people.

Genetic risk

Dr Hornig’s research, based on the Norwegian Mother, Father and Child Cohort Study of more than 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 per cent 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In preliminary, unpublished work, Dr Hornig’s team also saw hints that acetaminophen taken for pain may carry different risks.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 that the findings need more study.

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

The findings underscore what scientists have long said: Autism does not have a single cause. Genetics, timing and environment all interact, Dr 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.

Dr 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 metabolise the drug.

Some labs are testing newborns’ meconium for toxic by-products of acetaminophen metabolism – a potential biomarker that could guide safer choices in the future.

“Our future generations deserve a personalised 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 is not considered safe later in pregnancy.

But Dr 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. BLOOMBERG