A U.S. appeals court on Monday reversed a trial judge’s decision to dismiss lawsuits against the makers of Tylenol, reviving hundreds of cases filed by families who claim that their children developed autism or attention-deficit/hyperactivity disorder after their mothers took Tylenol during pregnancy.

The judges, all Democratic appointees, ruled that the lower court overstepped by excluding scientific evidence presented by expert witnesses on behalf of the plaintiffs. That expert testimony, the judges argued, was valid evidence about a scientific question that they said was still under dispute.

The decision came less than a year after President Donald Trump and top health advisers warned that taking acetaminophen, the active painkiller in Tylenol, while pregnant could cause autism and ADHD in children. That link is unproven: While some studies have suggested there may be a small increase in risk, large trials aiming to account for underlying genetics and other factors have found no evidence that the painkiller can cause neurodevelopmental disorders in children.

Major medical groups, including the American College of Obstetricians and Gynecologists, have consistently stressed that Tylenol is the safest option to treat pain or fever during pregnancy.

At the center of the appeals court decision was the question of whether the scientific evidence presented by the plaintiffs held merit. The primary expert witness for the plaintiffs was Andrea Baccarelli, the dean of the Harvard T.H. Chan School of Public Health, who submitted a report claiming that “substantial evidence” supported a causal link between use of acetaminophen during pregnancy and neurodevelopmental disorders such as autism and ADHD in children, especially when taken frequently at high doses.

Ashley Keller, a lawyer for the main law firm representing the plaintiffs, Keller Postman, said Monday’s ruling represented “vindication for the scientific evidence our clients have presented from the outset.”

The defendants in the suits are Kenvue, which has been the maker of Tylenol since it was spun off from Johnson & Johnson in 2023, and major retailers that sell generic versions of acetaminophen.

“The procedural ruling today does not change the fact that credible, independent science shows no proven link between taking acetaminophen and autism or attention-deficit/hyperactivity disorder,” said Melissa Witt, a spokesperson for Kenvue. “Science matters, and we stand with the many public health and medical professionals who have reviewed the science on this topic and agree.”

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This article originally appeared in The New York Times.

By Azeen Ghorayshi
c. 2026 The New York Times Company