Trump promotes unproven theory about Tylenol and autism. What does the science say?

One day after claiming his administration has “found an answer to autism,” President Trump announced new efforts on Monday to warn Americans that taking Tylenol and other acetaminophen-based pain relievers during pregnancy could be linked to the neurological condition — and to encourage the use of leucovorin, a lesser-known cancer and anemia drug, to treat it.

But both theories are unproven, and Trump did not provide any new evidence to back up his administration’s new recommendations.

“I always had very strong feelings about autism and how it happened and where it came from,” the president insisted. “We understood a lot more than a lot of people who studied it.”

Since returning to the Oval Office in January, Trump has repeatedly pledged to address America’s rising autism rate. In April, Health and Human Services Secretary Robert F. Kennedy Jr., who has long promoted debunked theories about the disorder, said that the administration had “launched a massive testing and research effort that’s going to involve hundreds of scientists from around the world,” promising that “by September, we will know what has caused the autism epidemic, and we’ll be able to eliminate those exposures.”

Kennedy did not deliver on that promise on Monday. Instead, he said the National Institutes of Health would continue to examine “multiple” hypotheses about potential causes and start awarding 13 research grants this month, with updates likely next year.

But Trump and Kennedy, along with other administration officials, did claim that prenatal exposure to acetaminophen, the active ingredient in Tylenol and one of the most widely used medications globally, might increase the risk of autism spectrum disorder (ASD) — and as a result the Food and Drug Administration issued a new recommendation that pregnant people should only take it for high fevers.

Officials also highlighted research showing that folinic acid (a form of vitamin B9), also called leucovorin — a decades-old medication that’s often prescribed to counteract the toxic effects of a certain cancer drug — could help boost communication and cognition in at least some individuals with autism.

During Monday’s announcement, Kennedy continued his efforts to link childhood vaccines to autism — a claim that has been thoroughly debunked. Calling ASD a “complex disorder,” he insisted there would be “no areas of taboo” in future research. “One area we are closely examining is vaccines,” Kennedy said. “It will take time for an honest look at this topic by scientists. We will be uncompromising and relentless in our search for answers.”

The rest of Monday’s announcement wasn’t based on similarly discredited science. But experts don’t consider it “an answer to autism” either.

What we know about Tylenol and autism

Recent studies have come to conflicting conclusions about acetaminophen. In August, the journal BMC Environmental Health published a review of the existing research — including six studies on the association between prenatal acetaminophen use and the risk of ASD in children — that purported to find “strong evidence of a relationship” between the drug and the disorder.

The paper was coauthored by Dr. Andrea Baccarelli, the dean of Harvard’s T.H. Chan School of Public Health, and it ultimately recommended “judicious acetaminophen use — lowest effective dose, shortest duration — under medical guidance, tailored to individual risk-benefit assessments.”

Yet a large 2024 study, which looked at nearly 2.5 million people born in Sweden between 1995 and 2019, concluded that “acetaminophen use during pregnancy was not associated with children’s risk of autism.”

Why the difference? Like other researchers, the Swedish team discovered an increased prevalence of autism among the offspring of people who took acetaminophen during pregnancy. But the risk was only a little higher, according to their study — 0.09 percentage points, to be exact — and it disappeared when they zeroed in on sibling-pair cases where the parent took acetaminophen during one pregnancy and not the other.

“This suggests that what initially looked like an elevated risk of autism from acetaminophen during pregnancy may have been a result of other risk factors,” Scientific American recently explained — namely, “the fever or underlying infections Tylenol was used to treat.” (A 2014 study of more than 2 million people found that if a pregnant person is hospitalized with an infection, the likelihood that their child will develop autism increases by approximately 30%.)

“The conditions people use acetaminophen to treat during pregnancy are far more dangerous than any theoretical risks and can create severe morbidity and mortality for the pregnant person and the fetus,” the American College of Obstetricians and Gynecologists said in a statement.

What we know about leucovorin and autism

Meanwhile, leucovorin has shown promise as a possible autism treatment — but it’s far too early to draw any definitive conclusions about its efficacy.

Scientists have long known that folate deficiency during pregnancy can increase the risk of neural tube defects. (The neural tube eventually develops into the brain and spinal cord.) In 2004, a study found that some children with autism-like symptoms have a condition that makes it harder for their bodies to transport folate to their brains. As a result, researchers in Arizona, France, China, India and Iran have conducted small, randomized controlled trials of folinic acid as a treatment for autism — i.e., as a way to help deliver folate more effectively — and all have found modest improvements in receptive and expressive language.

Still, only a few dozen children participated in each of these studies, and larger trials of leucovorin have been slow to launch because its original patents have expired (leaving pharmaceutical companies with little incentive to fund further research).

Controversial claims

Monday’s announcement is likely to prove controversial in the autism community. ASD diagnoses have risen by about 300% over the past 20 years — a shift Trump attributed mainly to environmental factors.

“There’s something artificial,” he claimed on Monday. “They’re taking something.”

In contrast, a half-century of research shows that ASD is “a complex neurodevelopmental condition that arises from a constellation of genetic factors and environmental influences,” as Scientific American put it, and most public health officials attribute rising rates to a broader definition of the disorder — along with increased screening and awareness — rather than some sort of toxin.

So while the promise of singular causes and silver bullet cures might draw attention, experts warn that getting ahead of the existing science could backfire on families.

“A press statement that talks about a potential association will cause lots of fear,” Dr. Debra Houry, former chief medical officer of the Centers for Disease Control and Prevention, told reporters Monday morning. “If there is not the science to back it up, we will see practice changes, worried moms, all sorts of things, and that’s not appropriate.”