President Trump and prominent federal health officials on Monday launched a sweeping challenge to the established scientific understanding of autism. Without presenting new evidence, they asserted that acetaminophen, the active ingredient found in the common pain reliever Tylenol, is a cause of the disorder.
These officials, including Health Secretary Robert F. Kennedy Jr. and Food and Drug Administration Commissioner Dr. Marty Makary, also endorsed leucovorin, a B-vitamin-based medication, as a treatment for autism. This drug has only undergone limited study in a small number of research participants.
Furthermore, new research initiatives were announced, dedicating millions of federal dollars to investigate the environmental origins of autism. This includes revisiting a long-discredited theory that suggests vaccines as a contributing factor.
Collectively, these announcements signal a significant shift, reframing autism as a neglected health crisis driven by environmental causes that, they claim, have been overlooked by politically motivated researchers. Most scientists, however, maintain that this neurological condition arises from a complex interaction of genetic and environmental influences.
The White House briefing was marked by President Trump’s frequent delivery of unsubstantiated medical advice, echoing his first term when he promoted unproven Covid treatments.
On Monday, the president repeatedly issued stern warnings that directly contradicted the recommendations of leading medical organizations: “Don’t take Tylenol. Don’t take it. Fight like hell not to take it.” He urged expectant mothers to endure pain, except in rare emergencies like dangerously high fevers.
For years, scientists have explored a potential connection between acetaminophen and autism, but studies have consistently yielded inconclusive results. Mainstream medical groups swiftly reaffirmed acetaminophen as a safe option for managing fever during pregnancy, provided it’s not used for extended periods.
Secretary Kennedy acknowledged that autism is a “multi-factorial” condition, yet focused heavily on vaccines. He has long contended that vaccines are at least partially responsible for the increasing rates of autism diagnoses in children. Both he and President Trump accused health agencies from previous administrations of deliberately ignoring vaccine risks and dismissed genetic research into the neurodevelopmental disorder.
Decades of studies have failed to establish any link between vaccines and autism, and the scientific community widely agrees that this theory has been disproven.
President Trump noted his long-standing discussions with Secretary Kennedy regarding a possible vaccine link. He further echoed Kennedy’s views, stating that the childhood immunization schedule “loads up” children with too many vaccines. The president claimed, without evidence, that infants are administered as many as 80 different injections.
“It’s too much liquid, too many different things are going into that baby at too big a number,” President Trump remarked.
The Food and Drug Administration adopted a more cautious tone, issuing a letter to doctors on Monday that accurately stated, “a causal relationship has not been established” between acetaminophen and autism. The agency described the issue as “an ongoing area of scientific debate.”
When asked about the letter, external experts confirmed that it does not alter standard medical practice, which already advocates minimizing medication use, including acetaminophen, during pregnancy.
“Doctors have always approached medications in pregnancy by using it only when indicated, lowest dose, for the shortest duration,” explained Dr. Nathaniel DeNicola, an adviser to the American College of Obstetricians and Gynecologists on environmental matters.
“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 emphasized.
He also highlighted that while the FDA’s letter to physicians suggested acetaminophen only for low-grade fevers, the definition of a low-grade fever was unclear.
Medical professionals typically recommend treating fevers during pregnancy (defined as anything above 100.4 degrees Fahrenheit) due to potential risks for both mother and fetus, including neurodevelopmental concerns. Acetaminophen is considered one of the few safe choices for pain or fever relief during pregnancy.
Given its widespread use, concerns about acetaminophen and developmental issues in children have persisted for a long time. However, scientists overwhelmingly agree that autism results from a complex combination of genetic and environmental factors, and that the rising diagnostic rates cannot be attributed to a single cause.
During the announcement, health officials frequently referenced a recent scientific review conducted by epidemiologists at Harvard T.H. Chan School of Public Health and the Icahn School of Medicine at Mount Sinai.
That article, which analyzed existing scientific studies without conducting its own birth outcome analysis, suggested there was evidence of a link between acetaminophen use during pregnancy and neurodevelopmental disorders like attention deficit hyperactivity disorder and autism.
Dr. Makary stated at the news conference that Dr. Andrea Baccarelli, dean of Harvard’s public health school and a co-author of the review, had indicated it demonstrated a causal relationship between the pain reliever and autism.
In a statement issued Monday night, Dr. Baccarelli clarified that further research is essential to establish a causal link. “But based on existing evidence, I believe that caution about acetaminophen use during pregnancy — especially heavy or prolonged use — is warranted,” he said.
Other authors of the review cautioned that their findings do not confirm 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 lead author of the study, previously told The New York Times.
Studies examining the potential risk to fetal brain development have produced mixed results. The review assessed 46 studies on a possible link between acetaminophen use during pregnancy and childhood neurodevelopmental issues, with eight specifically focusing on autism. More than half of these studies found a positive association.
Many health agencies, including the Food and Drug Administration and its European counterpart, have reviewed the evidence and concluded that the findings are inconclusive, meaning no established risk has been found.
Nevertheless, some scientists have suggested that health professionals adopt a precautionary approach and inform pregnant women about the potential for a link between acetaminophen and autism.
Most experts believe it would be unethical to conduct pharmaceutical research directly on pregnant women. This is why existing research on acetaminophen’s effects relies on observational studies, where researchers analyze data from women’s pregnancies and subsequent child development.
Consequently, researchers cannot account for all the ways in which women who use Tylenol during pregnancy might differ from those who do not.
Many studies included in the new review “did not necessarily go to the greatest lengths to account for possible confounders,” noted Dr. Brian Lee, a professor of epidemiology at Drexel University, referring to other factors that could explain a potential association.
“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 co-authored a significant study analyzing the health records of 2.5 million children born in Sweden. While this study initially found a small positive association between mothers who used acetaminophen and the incidence of autism, ADHD, and intellectual disability, this link vanished after a subsequent analysis comparing siblings born to the same mothers.
The sibling study’s results indicated that the actual cause might be maternal genetics, not acetaminophen, according to Dr. Lee.
Kenvue, the company marketing Tylenol, dismissed the suggestion of a link between its product’s use during pregnancy and autism. “We believe independent, sound science clearly shows that taking acetaminophen does not cause autism,” Melissa Witt, a spokeswoman for Kenvue, stated 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 most widely recognized among approximately 600 products containing acetaminophen, an analgesic. Nearly a quarter of U.S. adults use a medicine containing acetaminophen each week, according to a trade group for consumer health care products.
Tylenol has been available for 70 years, primarily manufactured by Johnson & Johnson for most of that time. In 2023, Johnson & Johnson spun off Tylenol and its other consumer brands into a new company, Kenvue.
On Monday, the FDA also announced its approval of leucovorin, an older generic drug, for the treatment of autism symptoms in certain children. This medication, available in tablet form, has historically been used to manage chemotherapy side effects.
The agency cited a review of medical literature, highlighting one study that compared roughly 40 children on the medication with 40 on a placebo, which the agency claimed demonstrated “substantial improvement.” The drug is specifically approved for individuals with “cerebral folate deficiency,” a subset of those diagnosed with autism.
GSK, which marketed the drug in the 1980s and 1990s, stated it would comply with the FDA’s request to update the drug’s labeling to reflect safe use for individuals with autism.
Pregnant women are already advised to consume folic acid early in pregnancy to support healthy fetal brain development.