The flimsy evidence behind Trump’s big autism announcement, explained

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During a highly anticipated announcement today, President Donald Trump urged pregnant people to avoid taking Tylenol if possible because of the painkiller’s possible link to autism.

At the same time, Trump promoted leucovorin, a decades-old medication that mimics folic acid and is often used to restore nutrients in patients who are taking chemotherapy drugs. The folate-based treatment has been investigated in a few small clinical trials as a possible therapeutic for children with autism.

Before we get any further: The link between Tylenol and autism is unclear, and physician groups still recommend the medicine for pregnant people experiencing pain or fever, in consultation with their doctor. The link between vaccines and autism has been studied exhaustively, and no connection has been found.

Delivering leucovorin could, in theory, improve symptoms — and, in those small experiments, some parents and investigators have been thrilled with the results, as well as the strong safety profile.

But the evidence here is also still very limited; one study involved fewer than 50 patients. It is not clear whether this drug would work for all patients on the autism spectrum.

Trump and Health Secretary Robert F. Kennedy Jr. have been promising the American public answers on autism for months. But Monday’s announcement outpaces any science that could adequately back up the administration’s guidance. The National Institutes of Health has undertaken a massive review of autism science, but, according to the Washington Post, that research review was not completed in time for Trump’s White House announcement.’

Kennedy has long theorized that there is a link between vaccines and autism, and Trump, too, indulged in the debunked theory that autism could be caused by vaccines during Monday’s announcement. Kennedy promised during the press conference to continue that search, accusing the medical establishment of “gaslighting” mothers who are concerned about the impact on their children. The Make America Healthy Again movement emphasizes, in general, the possibility that pharmaceutical drugs could be causing a number of health problems in America’s children.

Of course, many autism scientists and advocates are alarmed by the administration’s announcement. The evidence linking Tylenol to autism’s development is mixed — some studies have found an association, including a cohort study based out of Boston cited by Food and Drug Administration Commissioner Marty Makary at the press conference. The cohort research involved 1,000 children; a 2024 study that covered 2.5 million children in Sweden, however, concluded that no link exists.

Trump’s and Kennedy’s fixation that autism rates are rising — and that something must be driving that increase — misses some important context: Most autism scientists believe that increase is actually largely the result of more public awareness about autism, and the subtle ways that it can manifest, as well as a changing and expanding definition of what is classified as autism.

As for autism’s underlying causes, as I reported earlier this year, our country’s leading autism scientists have identified hundreds of genes that are associated with the development of autism-like symptoms. Those scientists acknowledge there may be some non-genetic factors that play a role — such as more people giving birth at a later age — but they dismiss previous claims by Kennedy that a single chemical toxin can explain the uptick in autism diagnoses.

The White House press conference “alarms us researchers who have committed our entire careers to better understanding autism,” said a statement from the Coalition of Autism Scientists. “The data cited do not support the claim that Tylenol causes autism and leucovorin is a cure, and only stoke fear and falsely suggest hope when there is no simple answer.”

Here’s what we actually know about Tylenol and autism, about the autism treatment that Trump pushed in his announcement, and about what may actually be driving the increase in autism cases.

The evidence linking Tylenol to autism is muddy

Trump said in his Oval Office announcement that the FDA would be notifying physicians of the risk of Tylenol during pregnancy. He said repeatedly, “Don’t take it,” unless you have an extremely high fever. (Current medical guidance already stipulates that a pregnant person should talk with their doctor before taking acetaminophen for fever or pain.)

Some scientists have argued in recent years that there may be a link between taking Tylenol during pregnancy and the development of autism. Most recently, a systematic review of six studies on the matter, co-authored by the Harvard School of Public Health’s dean in August of this year, concluded there was an association between Tylenol (also known as acetaminophen in its generic form) and the onset of autism. But finding an association is not the same thing as proving a cause, and the authors of the systematic review acknowledged this.

Other scientists, too, pointed out limitations with the Harvard evidence review. For one, several of the studies included were small: One involved only 215 children. Second, most were observational studies that could have difficulty controlling for confounding factors, like the parents’ genetic disposition toward autism, or other drugs the pregnant person may have taken. For example, fever itself is already known to be a risk factor for autism and other neurodevelopmental problems in fetuses. If a pregnant person took Tylenol to treat their fever, an observational study would struggle to differentiate between whether the pain medication or the fever contributed to a child being born with autism.

And lastly, by far the largest study included in the analysis — the one that covered 2.5 million children in Sweden; the next largest study involved 73,000 children across Europe — concluded there was no link between Tylenol and autism after controlling for confounding factors.

When taken together, the link between Tylenol and autism is still unclear, and Monday’s announcement risks overstating the painkiller’s dangers to developing babies. “Regarding Tylenol in pregnancy, this is rushed science and not yet borne out in the data,” Stephen Scherer, director of the Center for Applied Genomics at the Hospital for Sick Children in Toronto, told me.

Discouraging pregnant people from taking Tylenol has its own risks.

Even the authors of the meta-analysis that showed a link argued only for judicious use of the drug, not eliminating it entirely. Pregnant people are already discouraged from taking ibuprofen because of a more serious risk of birth defects, leaving acetaminophen as their first and most reliable choice for relieving pain and fevers.

What we really know about the increase in autism rates

The increase in autism diagnoses is very real: According to a sweeping 2000 analysis by the Centers for Disease Control and Prevention, a range of 2 to 7 per 1,000, or roughly 0.5 percent of US children, were diagnosed with autism in the 1990s. That figure has risen to 1 in 35 kids, or roughly 3 percent.

For a long time, the process for diagnosing a person with autism was strictly based on speech development. But today we have criteria that include a wide range of social and emotional symptoms with three subtypes — the autism spectrum disorder we’re familiar with today.

It makes sense, then, that as the criteria for autism expanded, more and more children would meet it, and autism rates would rise. And that’s precisely what happened.

Other known risk factors — like more people now having babies later in their life, given that parental age is linked to a higher likelihood of autism — are more likely to be a factor than anything Kennedy has been pointing at, experts told me earlier this year.

“It’s very clear it’s not going to be one environmental toxin,” Alison Singer, founder of the Autism Science Foundation and parent of a child with profound autism, told me back in May. “If there were a smoking gun, I think they would have found it.”

Instead, many autism scientists continue to focus on genetics. Multiple studies have attributed about 80 percent of a person’s risk of developing autism to their inherited genetic factors. Clinical trials for gene-based therapies are getting underway, offering another avenue for providing relief to patients and families — but one that Kennedy, who called genetics a dead end for understanding autism, and the Trump administration have so far ignored.

The administration itself seems to acknowledge that Tylenol is far from a smoking gun; that’s why the NIH’s research efforts are still ongoing. But after promising for months to deliver some kind of answer on autism, this seems to be the best they could come up with.