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Research tying Tylenol to autism lost in court. Then it won Trump’s ear.

A year ago, the maker of Tylenol lauded a federal judge’s dismissal of hundreds of lawsuits alleging the popular painkiller caused autism in children whose mothers took it during pregnancy. The company, Kenvue Inc., citing “confusion” the litigation caused, said the judge’s ruling affirmed that “science does not support causation.”

But now Kenvue and its premier over-the-counter drug have been thrust into a political and medical maelstrom after President Donald Trump - in a White House briefing Monday - amplified the losing side of the court cases with his powerful megaphone.

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In forcefully warning expectant mothers not to take Tylenol no less than a dozen times, Trump drew on evidence that is unsettled, disputed and that failed to pass legal scrutiny in U.S. District Court in New York.

A research paper published last month that the White House and Health and Human Services Secretary Robert F. Kennedy Jr. relied upon Monday to buttress their argument was published by a prominent academic who court records show received $150,000 as an expert witness in the litigation.

The episode reveals a nexus of large-scale litigation, medical claims seized upon by parents desperate for answers and the MAHA political movement that Kennedy has led and brought to the forefront of Trump administration policies.

The verdict on Tylenol remains inconclusive, medical specialists say, with a suggestion of potential concern in some studies but contradictory findings in others and no solid evidence that taking it while pregnant is harmful.

Now, as the Food and Drug Administration moves to amend Tylenol’s label with a warning about the potential link between its use during pregnancy and autism, Kenvue is bracing for another tsunami of litigation, according to a person close to the company who spoke on the condition of anonymity to discuss a sensitive situation.

“What they say isn’t going to change the truth, but it could have a commercial impact,” the person said.

The official statement by the FDA accompanying Trump’s comments was far more measured, acknowledging considerable scientific debate over whether pregnant women taking acetaminophen - the active ingredient in Tylenol - can cause autism in their children. But parents and physicians are scrambling to assess the safety of the drug amid a wave of conflicting signals and outrage by clinical experts and advocacy groups who say the administration overstepped.

Kenvue said in a statement that “independent, sound science clearly shows that taking acetaminophen does not cause autism,” adding that it will “explore all options to protect the health interests of American women and children.”

HHS didn’t respond to a request for comment Wednesday.

The federal acetaminophen cases against Kenvue are currently being appealed. Ashley Keller, a lawyer representing plaintiffs, said that the administration’s position could help their cause “from an atmospheric perspective,” bolstering the credibility of their expert witnesses.

“If you hear something official from the president of the United States and the secretary of HHS,” he added, “I do think that’s going to impact behavior.”

The Trump administration’s statements linking acetaminophen to autism rest heavily on a researcher with sterling academic credentials - whose 2025 published paper was a modified and expanded version of the work that was thoroughly rejected by the judge overseeing the case.

Andrea Baccarelli, a prominent epidemiologist, now serves as dean of the Harvard T.H. Chan School of Public Health. Before 2024 he was a professor at the Columbia University Mailman School of Public Health, and as recently as early 2020 he had taken the position that research showed no link between acetaminophen and autism.

But during that year, he testified in his deposition, he did a “deep dive in the literature, and I started to believe at the end of 2020 that there was a problem.” His concerns grew, he said, and by 2022 his view had flipped to being concerned about the link to autism. In December of that year, he was hired as an expert witness at a rate that he disclosed in his deposition was $700 an hour.

In a 148-page opinion in December 2023, U.S. District Judge Denise Cote of the Southern District of New York took a dim view of his reliability. She sharply criticized Baccarelli’s work, citing multiple flaws: cherry-picking weak studies that found links while downplaying stronger ones that didn’t; lumping together autism and attention-deficit/hyperactivity disorder despite them being distinct conditions; and failing to account for confounding factors, like whether fever itself - rather than acetaminophen - might explain the association.

Cote called parts of Baccarelli’s analysis “troubling” and “cursory,” writing that his “failure to engage seriously with the complexity of the relevant studies’ outcomes is well illustrated.”

But Baccarelli’s work has gained new life and visibility, serving as the foundation for the widely circulated journal article published last month. The paper in BMC Environmental Health analyzes previously published studies on acetaminophen during pregnancy and its link to autism, concluding that there appears to be an association but that their data cannot prove causation.

Harvard spokesperson Stephanie Simon said Baccarelli was not available for an interview and declined to respond to questions other than to say that he “just worked a few hours on the case after the deposition.” Two of Baccarelli’s three co-authors - from Mount Sinai and the University of Massachusetts Lowell - said they stand by the paper but declined to answer questions about his previous work and role in the study.

For nearly four decades, scientists have examined whether taking acetaminophen during pregnancy is associated with neurodevelopmental disorders, including autism and ADHD. Such scrutiny gained steam with two studies in 2016 and 2019 that linked the use of acetaminophen prenatally to autism, and a “consensus statement” in 2021 by 13 authors calling on health professionals to caution pregnant women to the medication “at the lowest effective dose for the shortest possible time.”

Scientists who’ve studied the issue say that establishing causation between environmental exposures and disease is notoriously difficult, often impossible, due to the complexity of variables and ethical constraints that make gold-standard clinical trials unfeasible. Scientific disagreement over methodology is common, they said, and doesn’t necessarily indicate flawed research.

Kenvue, spun out of Johnson & Johnson in 2023, has been fending off lawsuits linking Tylenol to autism since 2022.

One law firm that took an early interest was Wisner Baum, which Kennedy, a personal injury and environmental lawyer, previously consulted for. The firm was soliciting plaintiffs who took Tylenol or other medications while pregnant and whose children developed autism or other disorders, The Washington Post found in a review of internet archives. The call-out for plaintiffs was listed on their website from at least the end of January 2023 through part of May this year, at one point with the words “AWARD-WINNING ATTORNEYS PURSUING TYLENOL LAWSUIT COMPENSATION FOR AMERICAN FAMILIES.”

However, on an April 2024 podcast, the firm’s managing partner, R. Brent Wisner, said he chose not to get involved in the Tylenol class-action lawsuit.

“I did not get into the Tylenol autism case, not because I didn’t think it had merit or because it was a solid case,” he said. But after looking at the science, he said, “I didn’t want to pursue it.”

During Kennedy’s confirmation hearings, he faced immense pressure to divest from a financial stake he initially said he would keep in cases he referred to Wisner Baum before becoming secretary. Kennedy has disclosed he gave the stake to an adult family member who is licensed to practice law in California. One of Kennedy’s sons, Conor Kennedy, is listed as working at Wisner Baum in its Los Angeles office.

Wisner Baum didn’t immediately respond to a request for comment Wednesday.

For Kenvue, Tylenol has been a mainstay of its business in the midst of turmoil. The New Jersey-based company lost three top executives in recent months, including its CEO and chief financial officer. It launched a strategic review as its skin health and beauty business struggled.

Even during the course of the Tylenol litigation, Kenvue “actually continued to gain market share for Tylenol,” said Navann Ty, a health care analyst for BNP Paribas Exane, estimating the medication accounts for about 10 percent of Kenvue’s $15.5 billion in annual revenue.

Instead, the company may be facing a different kind of challenge. “We believe there could be risk to Tylenol consumption given the HHS recommendation may push consumers to reduce consumption of the brand owing to the negative headlines, which may lead a broader set of consumers (not only pregnant women) to shift to other pain reduction methods,” Filippo Falorni, a Citi Research analyst, wrote in a note to clients Monday.

Kenvue shares have fallen about 16 percent since reports that HHS would tie acetaminophen to autism earlier this month, according to S&P Global Market Intelligence data. The company’s stock edged up Tuesday after regulatory actions that investors perceived as moderate.

Beate Ritz, one of the co-authors of the Environmental Health study and a UCLA Fielding School of Public Health professor of epidemiology, said that she was invited about a year ago by Baccarelli to help with the study. She said he disclosed his work with the lawsuit and hoped Ritz - an expert in research bias who worked on a large acetaminophen paper several years earlier - could help bring fresh eyes to the analysis. She said she recommended a number of changes, almost all of which Baccarelli agreed with.

“I felt this was a honest approach to a very complicated problem,” she said. “But then it became very politicized with the administration picking it and it’s becoming a nightmare in my mind.”

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Lena H. Sun contributed to this report.

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