On Monday, former President Trump, alongside top federal health officials, initiated a significant challenge to the conventional understanding of autism. Without presenting any new scientific evidence, they asserted that acetaminophen, the common pain reliever found in Tylenol, is a cause of the disorder.
Among these officials were Health Secretary Robert F. Kennedy Jr. and the Food and Drug Administration (FDA) commissioner, Dr. Marty Makary. They also endorsed leucovorin, a B-vitamin-based drug, as a treatment for autism, despite its limited study in only dozens of research participants.
Furthermore, they announced a substantial federal investment into new research on the root causes of autism, specifically targeting environmental factors. This includes revisiting the long-discredited theory that vaccines are to blame for the condition.
These pronouncements signal a shift towards portraying autism as a neglected epidemic driven by environmental factors, which they claim have been overlooked by politically motivated researchers. Most scientists, however, attribute the neurological disorder to a complex interplay of both genetic and environmental elements.
The White House briefing was marked by President Trump’s issuance of medical advice that often lacked scientific backing, reminiscent of his first term when he promoted unproven COVID-19 treatments.
The president repeatedly urged strong warnings against Tylenol: “Don’t take Tylenol. Don’t take it. Fight like hell not to take it.” He advised pregnant women to “tough it out” when experiencing pain, reserving medication only for severe cases like dangerously high fevers.
For years, scientists have explored a potential connection between acetaminophen and autism, but current studies remain inconclusive. Mainstream medical groups quickly reiterated that acetaminophen is a safe and effective treatment for fever in pregnant women, provided it’s not used long-term.
Health Secretary Kennedy acknowledged autism as a “multi-factorial” disease but heavily emphasized vaccines, a long-held belief of his regarding the rising incidence of autism in children. Both he and President Trump accused health agencies from previous administrations of deliberately ignoring vaccine risks and dismissed existing research on the genetic underpinnings of the neurodevelopmental disorder.
Decades of studies have consistently found no link between vaccines and autism, with the scientific community largely debunking the theory.
President Trump recalled his long-standing discussions with Kennedy about a possible vaccine link. He further echoed Kennedy’s perspective, stating, without evidence, that the childhood immunization schedule “loads up” children with too many vaccines, claiming babies receive 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,” Trump asserted.
The FDA, in contrast, was more cautious. On Monday, it issued a letter to doctors accurately noting that “a causal relationship has not been established” between acetaminophen and autism, describing it as “an ongoing area of scientific debate.”
External experts, when asked about the letter, confirmed that it did not alter standard medical practice, which already advocates for 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 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 affirmed.
He also noted that while the FDA’s letter suggested acetaminophen for low-grade fevers, it didn’t clearly define what constitutes a low-grade fever.
Doctors typically recommend treating fevers above 100.4 degrees Fahrenheit during pregnancy due to potential risks to both mother and fetus, including neurodevelopmental issues. Acetaminophen is considered one of the few safe options for pain or fever relief during pregnancy.
Given its widespread use, concerns about acetaminophen and developmental problems in children have persisted. However, scientists largely agree that autism stems from a complex combination of genetic and environmental factors, and its rising diagnosis rates cannot be attributed to a single cause.
During the announcement, health officials repeatedly referenced a recent scientific review conducted by epidemiologists from Harvard T.H. Chan School of Public Health and the Icahn School of Medicine at Mount Sinai.
This article, which synthesized existing research without conducting new analysis of birth outcomes, suggested there was evidence of a link between prenatal acetaminophen use and neurodevelopmental disorders such as attention deficit hyperactivity disorder and autism.
Dr. Makary claimed at the news conference that Dr. Andrea Baccarelli, dean of Harvard’s public health school and a co-author of the review, stated it demonstrated a causal relationship between the pain reliever and autism.
In a statement issued Monday night, Dr. Baccarelli clarified that more 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 also emphasized that their findings did not prove a cause-and-effect relationship between acetaminophen and autism.
“We cannot answer the question about causation — that is very important to clarify,” Dr. Diddier Prada, an epidemiologist at Mount Sinai and the study’s first author, explained earlier this month.
Studies on the potential risk to fetal brain development have produced mixed results. The review examined 46 studies on a possible link between acetaminophen use during pregnancy and childhood neurodevelopmental issues, with eight specifically on autism. Over half of these studies found a positive association.
Many health agencies, including the FDA and its European counterpart, have reviewed the evidence and concluded that the findings are inconclusive, indicating no established risk.
Nonetheless, some scientists have advocated for a precautionary approach, advising health professionals to warn pregnant women about a possible link between acetaminophen and autism.
Most experts contend that conducting pharmaceutical research on pregnant women would be unethical. Consequently, existing research on acetaminophen’s effects relies on observational studies, analyzing data from women’s pregnancies and tracking their children’s development over time.
As a result, researchers cannot fully account for all the differences between women who take Tylenol during pregnancy and those who do not.
Many studies in the recent 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 might explain a perceived link.
“And the biggest elephant in the room here,” he added, “is genetic confounding, because we know autism, ADHD, 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 in Sweden. While an initial analysis showed a small positive association between mothers who used acetaminophen and the incidence of autism, ADHD, and intellectual disability, this link vanished when they conducted a subsequent analysis comparing siblings born to the same mothers.
The sibling study’s findings suggested that maternal genetics, rather than acetaminophen, could be the true underlying cause, Dr. Lee concluded.
Kenvue, the company marketing Tylenol, refuted the idea 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 Kenvue spokeswoman, 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. A trade group for consumer healthcare products indicates that nearly a quarter of U.S. adults use an acetaminophen-containing medicine weekly.
Tylenol has been available for 70 years, primarily manufactured by Johnson & Johnson. In 2023, Johnson & Johnson spun off Tylenol and other consumer brands into a new company, Kenvue.
On Monday, the FDA also announced its approval of leucovorin, an old generic drug, to address autism symptoms in certain children. This medication, approved in tablet form, has historically been used to mitigate chemotherapy side effects.
The agency referenced a review of medical literature, highlighting one study comparing about 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 subgroup within the autism spectrum.
GSK, which previously marketed the drug in the 1980s and 1990s, stated its compliance with the FDA’s request to update the drug’s labeling to suggest safe use for individuals with autism.
Pregnant women are already advised to consume folic acid early in pregnancy to support healthy fetal brain development.