President Trump and top federal health officials on Monday launched a broad offensive against the mainstream understanding of autism. Without presenting new evidence, they claimed that acetaminophen — the active ingredient in the common pain reliever Tylenol — was a cause of the disorder.
The officials, including Health Secretary Robert F. Kennedy Jr. and the commissioner of the Food and Drug Administration, Dr. Marty Makary, also endorsed a B-vitamin-based drug, leucovorin, to treat autism. This drug has only been studied in dozens of research participants.
Additionally, they announced new research into the root causes of autism, committing millions of federal dollars to study environmental factors, including a long-discredited theory that blames vaccines.
Collectively, these announcements marked a new step toward reframing autism as a neglected epidemic with environmental causes that politicized researchers have long been blind to. Most scientists believe that the neurological disorder results from a complex interplay of genetic and environmental factors.
Health Secretary Robert F. Kennedy Jr. has been a skeptic of vaccines. (Credit: Doug Mills/The New York Times)
The briefing at the White House featured often unsubstantiated medical advice from Mr. Trump, reminiscent of his first term, when he encouraged Americans to try unproven treatments for Covid.
The president on Monday repeatedly issued strong warnings that flew in the face of the recommendations of leading medical groups: “Don’t take Tylenol. Don’t take it. Fight like hell not to take it.” He urged pregnant women to “tough it out” when in pain, except in rare instances, such as a dangerously high fever.
Scientists have conducted research on a potential connection between acetaminophen and autism for years, but the studies have so far yielded inconclusive results. Mainstream medical groups quickly defended acetaminophen as a safe treatment for fever in pregnant women, although not to be used long-term.
Mr. Kennedy noted that autism was a “multi-factorial” disease, but then disproportionately focused on vaccines, which he has long argued are at least partly to blame for the rising incidence of autism in children. He and Mr. Trump both accused health agencies of previous administrations of purposely turning a blind eye to vaccine risks and dismissed research on the genetics of the neurodevelopmental disorder.
Dozens of studies over the last three decades have failed to find any link between vaccines and autism, and the consensus among scientists is that the idea has been debunked.
Mr. Trump mentioned that he and Mr. Kennedy had long discussed the possibility of a vaccine link. He also amplified Mr. Kennedy’s views, saying that the childhood immunization schedule “loads up” children with too many vaccines. The president said, without evidence, that babies are being given as many as 80 different shots.
“It’s too much liquid, too many different things are going into that baby at too big a number,” Mr. Trump said.
The Food and Drug Administration was far more circumspect, issuing a letter to doctors on Monday that noted, accurately, that “a causal relationship has not been established” between acetaminophen and autism. It stated that the matter is “an ongoing area of scientific debate.”
Asked about the letter, outside experts said it did not change standard medical practice, which already advises minimizing the use of medications, including acetaminophen, during pregnancy.
“Doctors have always approached medications in pregnancy by using it only when indicated, lowest dose, for the shortest duration,” said Dr. Nathaniel DeNicola, an adviser to the American College of Obstetricians and Gynecologists on environmental issues.
“That applies to Tylenol tomorrow the same as it does today, the same as it did yesterday. That is the standard of care: to only use medications when indicated during pregnancy and judiciously,” Dr. DeNicola said.
He pointed out that while the F.D.A.’s letter to physicians indicated that acetaminophen only be used to treat low grade fevers, it is not clear how they defined what a low-grade fever is.
Doctors recommend treating fevers during pregnancy, defined as anything above 100.4 degrees Fahrenheit, because of the risks for both the mother and the fetus, including the risk of neurodevelopmental issues. Acetaminophen is considered one of the few safe options to treat pain or fever during pregnancy.
Because of its widespread use, concerns about acetaminophen and developmental problems in children have been longstanding. Yet scientists overwhelmingly agree that autism results from a complex mix of genetic and environmental factors, and that the rising rates of autism diagnoses cannot be ascribed to just one factor.
In the announcement, health officials repeatedly referred to a recent scientific review by epidemiologists at Harvard T.H. Chan School of Public Health and the Icahn School of Medicine at Mount Sinai.
That article, which reviewed existing scientific studies and did not conduct its own analysis of birth outcomes, concluded that there was evidence of a link between acetaminophen use during pregnancy and neurodevelopmental disorders like attention deficit hyperactivity disorder and autism.
Dr. Makary said at the news conference that Dr. Andrea Baccarelli, the dean of Harvard’s public health school and a co-author of the review, had said it showed there was a causal relationship between the pain reliever and autism.
But other authors of the review cautioned that the findings did not mean that there was a cause and effect relationship between the pain reliever and autism.
“We cannot answer the question about causation — that is very important to clarify,” Dr. Diddier Prada, an epidemiologist at Mt. Sinai and the first author on the study, told The New York Times this month.
Studies that have examined the possible risk posed to fetal brain development have been mixed. The review evaluated 46 studies examining a possible link between acetaminophen use during pregnancy and neurodevelopmental issues in childhood, including eight studies that looked specifically at autism. More than half of the studies found a positive association.
Many health agencies — including the Food and Drug Administration and its European equivalent — have evaluated the evidence and concluded that the findings are inconclusive, meaning they found that there is no established risk.
Still, some scientists have recommended that health professionals take a precautionary stance and warn pregnant women about the possibility of a link between acetaminophen and autism.
Most experts believe that it would be unethical to perform pharmaceutical research on pregnant women, which is why the existing research on the effects of acetaminophen were observational, meaning that researchers analyzed data on women’s pregnancies and then looked at how their children do over time.
As a result, researchers cannot account for all of the ways in which women who take Tylenol during their pregnancies may differ from the women who do not.
Many of the studies included in the new review “did not necessarily go to the greatest lengths to account for possible confounders,” Dr. Brian Lee, a professor of epidemiology at Drexel University, said, referring to other factors that might explain a potential link.
“And the biggest elephant in the room here,” he added, “is genetic confounding, because we know autism, A.D.H.D. and other neurodevelopmental disorders are highly heritable.”
In 2024, Dr. Lee was a co-author of a major study that analyzed the health records of 2.5 million children born in Sweden. While the study found a small positive association between women who used acetaminophen and the incidence of autism, A.D.H.D. and intellectual disability, that link disappeared after they did a subsequent analysis comparing siblings born to the same mothers.
The results of the sibling study indicated that the real cause could be maternal genetics, Dr. Lee said, not acetaminophen.
Kenvue, the company that markets Tylenol, rejected the notion of a link between the use of its product during pregnancy and autism. “We believe independent, sound science clearly shows that taking acetaminophen does not cause autism,” Melissa Witt, a spokeswoman for Kenvue, said a statement on Monday evening.
“We strongly disagree with any suggestion otherwise and are deeply concerned with the health risk this poses for expecting mothers and parents.”
Tylenol is the best known among some 600 products containing the active ingredient acetaminophen, an analgesic. Each week, nearly a quarter of U.S. adults use a medicine that contains acetaminophen, according to a trade group for consumer health care products.
Tylenol has been around for 70 years, made for most of that time by Johnson & Johnson. In 2023, Johnson & Johnson spun off Tylenol and other consumer brands to a new company, Kenvue.
On Monday, the F.D.A. also announced that it approved an old, generic drug called leucovorin for symptoms of autism in some children. The medication, approved in a tablet form, has largely been used to treat side effects of chemotherapy.
The agency cited a review of the medical literature, with emphasis on one study that compared about 40 children on the medication with 40 on a placebo that the agency said showed “substantial improvement.” The drug is specifically approved for people with “cerebral folate deficiency,” which is a subset of people with autism.
GSK, which marketed the drug in the 1980s and 1990s, said it would comply with the F.D.A.’s request to update the labeling of the drug to suggest safe use for people with autism.
Pregnant women are already advised to consume folic acid early in pregnancy to promote healthy brain development in the fetus.
Rebecca Robbins and Christina Jewett contributed reporting.