In a surprising move on Monday, President Trump and high-ranking federal health officials challenged the established scientific consensus on autism. Without presenting any new evidence, they asserted that acetaminophen, the active ingredient found in the widely used pain reliever Tylenol, is a cause of autism.
During the same announcement, officials like Health Secretary Robert F. Kennedy Jr. and FDA Commissioner Dr. Marty Makary also advocated for leucovorin, a B-vitamin-based medication, as an autism treatment. This drug has only undergone limited study, involving just a few dozen participants.
Furthermore, new federal research initiatives into the fundamental causes of autism were unveiled, promising millions in funding. These studies will explore environmental factors, controversially including the theory that vaccines are responsible — an idea that has been thoroughly discredited for years.
Collectively, these statements represent a significant shift, attempting to recharacterize autism as an overlooked epidemic with environmental origins, purportedly ignored by biased researchers. The vast majority of scientists maintain that this neurological disorder arises from intricate interactions between genetic predispositions and environmental influences.
The White House briefing was notable for President Trump’s frequent delivery of medical advice that lacked supporting evidence, echoing his previous term where he promoted unproven COVID-19 treatments to the public.
On Monday, the President issued stark warnings directly contradicting advice from prominent medical organizations, stating, “Don’t take Tylenol. Don’t take it. Fight like hell not to take it.” He advised pregnant women to endure pain, unless in critical situations like a dangerously high fever.
For years, scientists have explored a potential link between acetaminophen and autism, but their findings remain inconclusive. Despite this, mainstream medical organizations swiftly reaffirmed acetaminophen as a safe and effective treatment for fever in pregnant women, emphasizing that it should not be used for prolonged periods.
While acknowledging autism as a “multi-factorial” condition, Mr. Kennedy heavily emphasized vaccines, a subject he has consistently linked to the increasing rates of autism in children. Both he and Mr. Trump criticized past health agencies, alleging they deliberately overlooked vaccine risks, and downplayed research into the genetic underpinnings of this neurodevelopmental disorder.
However, numerous studies conducted over the past three decades have consistently found no connection between vaccines and autism, leading to a strong scientific consensus that this theory is baseless.
President Trump confirmed his long-standing discussions with Mr. Kennedy regarding a potential vaccine link. He further echoed Mr. Kennedy’s sentiments, claiming the current childhood immunization schedule overburdens children with vaccines and, without providing evidence, asserted that infants receive up to 80 shots simultaneously.
The Food and Drug Administration adopted a more cautious tone, releasing a letter to doctors on Monday. This letter accurately stated that “a causal relationship has not been established” between acetaminophen and autism, describing the issue as “an ongoing area of scientific debate.”
When questioned about the FDA’s letter, independent experts affirmed that it would not alter current medical practices. Standard guidelines already recommend minimizing all medication use during pregnancy, including acetaminophen.
Dr. Nathaniel DeNicola, an epidemiology professor at Drexel University, noted that many studies in the recent review “did not always thoroughly account for potential confounders,” referring to other variables that could explain an apparent link.
“This principle applies to Tylenol today, just as it did yesterday and will tomorrow. The standard of care emphasizes judicious medication use during pregnancy, only when clearly indicated,” Dr. DeNicola reiterated.
He also highlighted that while the FDA’s letter suggested acetaminophen should only be used for low-grade fevers, the specific definition of “low-grade” was left unclear.
Medical professionals generally advise treating fevers in pregnant women (temperatures exceeding 100.4 degrees Fahrenheit) due to potential risks for both mother and fetus, including neurodevelopmental concerns. Acetaminophen remains one of the limited safe options for pain or fever management during pregnancy.
Given its ubiquitous use, acetaminophen has long been scrutinized for its potential impact on childhood development. However, the scientific community largely agrees that autism stems from a multifaceted combination of genetic and environmental elements, and the increasing diagnosis rates cannot be attributed to a single cause.
Throughout their announcement, health officials repeatedly referenced a recent scientific review conducted by epidemiologists from the Harvard T.H. Chan School of Public Health and the Icahn School of Medicine at Mount Sinai.
This review, which synthesized existing scientific studies without conducting its own analysis of birth outcomes, indicated a possible association between acetaminophen use during pregnancy and neurodevelopmental disorders such as ADHD and autism.
At the press conference, Dr. Makary claimed that a co-author of the Harvard public health school review, its dean, had stated that the study demonstrated a causal link between the pain reliever and autism.
However, other authors involved in the review explicitly warned that their findings should not be interpreted as proving a cause-and-effect relationship between acetaminophen and autism.
“We are unable to definitively answer the question of causation — that is very important to clarify,” stated Dr. Diddier Prada, an epidemiologist at Mount Sinai and the lead author of the study.
Research into the potential risks of acetaminophen on fetal brain development has produced varied results. The review examined 46 studies exploring a possible link between prenatal acetaminophen exposure and neurodevelopmental conditions in children, with eight of these focusing solely on autism. Over half of these studies reported a positive association.
Numerous health organizations, including the Food and Drug Administration and its European counterpart, have reviewed the available evidence and determined that the findings are inconclusive, indicating no established risk.
Nevertheless, some scientists advocate for a precautionary approach, suggesting that healthcare professionals should inform pregnant women about the theoretical possibility of a link between acetaminophen and autism.
Given the ethical challenges of conducting pharmaceutical research on pregnant women, existing studies on acetaminophen’s effects are primarily observational. This means researchers analyze pregnancy data and track child development over time, rather than performing controlled experiments.
Consequently, researchers face limitations in fully accounting for all the differences between women who use Tylenol during pregnancy and those who do not, which could influence outcomes.
Dr. Brian Lee, an epidemiology professor at Drexel University, noted that many studies in the recent review “did not always thoroughly account for potential confounders,” referring to other variables that could explain an apparent link.
He further emphasized, “The most significant unaddressed issue here is genetic confounding, given that autism, ADHD, and other neurodevelopmental disorders are known to be highly heritable.”
In 2024, Dr. Lee co-authored a significant study involving 2.5 million Swedish birth records. Although it initially showed a minor positive association between maternal acetaminophen use and autism, ADHD, and intellectual disability, this link vanished when researchers compared siblings born to the same mothers.
The sibling study’s findings strongly suggested that maternal genetics, rather than acetaminophen itself, might be the underlying cause for any observed associations, according to Dr. Lee.
Kenvue, the company responsible for marketing Tylenol, refuted any connection between prenatal use of its product and autism. Melissa Witt, a Kenvue spokeswoman, stated on Monday evening, “We are confident that independent, rigorous science unequivocally demonstrates that acetaminophen does not cause autism.”
“We vehemently dispute any claims to the contrary and are profoundly worried about the potential health risks such misinformation presents to expectant mothers and parents,” she added.
Acetaminophen, an analgesic, is the active ingredient in Tylenol and approximately 600 other products. Each week, nearly a quarter of American adults use a medication containing acetaminophen, as reported by a consumer healthcare trade group.
Tylenol has been available for seven decades, largely produced by Johnson & Johnson until 2023, when the company spun off Tylenol and other consumer brands to form a new entity, Kenvue.
Separately on Monday, the FDA also announced the approval of leucovorin, an older generic drug, for managing autism symptoms in certain children. This tablet-form medication has historically been used to alleviate chemotherapy side effects.
The agency referenced a medical literature review, particularly highlighting one study. This study compared approximately 40 children receiving the medication with 40 children on a placebo, reportedly showing “substantial improvement” in the treated group. The drug’s approval is specifically for individuals with “cerebral folate deficiency,” a subgroup within the autism spectrum.
GSK, the pharmaceutical company that marketed leucovorin in the 1980s and 1990s, confirmed its compliance with the FDA’s request to update the drug’s labeling, recommending its safe use for individuals with autism.
It’s worth noting that pregnant women are already encouraged to take folic acid early in their pregnancy to support healthy fetal brain development.
Rebecca Robbins and Christina Jewett contributed reporting.