A federal appeals court on Monday revived more than 500 lawsuits against Kenvue, the maker of Tylenol, ruling that a lower court improperly excluded expert testimony offered by families who allege the pain reliever, when taken during pregnancy, contributed to autism spectrum disorder and attention-deficit/hyperactivity disorder in their children.

The decision by the 2nd U.S. Circuit Court of Appeals in Manhattan overturns a December 2024 ruling by U.S. District Judge Denise Cote, who had dismissed the cases after finding the plaintiffs’ scientific experts failed to meet the legal standard for admissible testimony. The appellate court ruled that portions of that testimony should instead be heard by a jury, reopening litigation that had appeared effectively over.

Importantly, the appeals court did not conclude that Tylenol causes autism or ADHD. Instead, the judges ruled only that several expert witnesses used sufficiently accepted scientific methods to allow their opinions to be presented in court.

Writing for the three-judge panel, Circuit Judge Guido Calabresi said three of the plaintiffs’ experts relied on methodologies accepted within the scientific community and offered “acceptable interpretations of scientific evidence where scientists may, and in fact do, disagree.” The panel agreed with the district court’s exclusion of two additional experts but concluded that excluding all five went too far.

The lawsuits allege that prolonged prenatal exposure to acetaminophen—the active ingredient in Tylenol—increases the likelihood that children later develop autism or ADHD. Plaintiffs contend consumers should have received stronger warning labels advising pregnant women of the alleged risks.

Kenvue strongly disputed those claims following Monday’s ruling.

“The overwhelming weight of credible scientific evidence continues to support the safety of acetaminophen when used as directed,” the company said in a statement. It added that the appellate ruling “does not change the science” and that it intends to continue defending the litigation.

Johnson & Johnson, which manufactured Tylenol for decades before spinning off Kenvue in 2023, has consistently maintained that extensive medical research has not established a causal relationship between appropriate acetaminophen use during pregnancy and autism or ADHD.

The financial implications are significant.

The revived litigation potentially exposes Kenvue to hundreds—and possibly thousands—of additional lawsuits nationwide. Investors reacted cautiously, sending the company’s shares modestly lower Monday as analysts reassessed potential legal liabilities.

The ruling also introduces new uncertainty for Kimberly-Clark, which announced plans to acquire Kenvue in a transaction valued at more than $40 billion. While Kimberly-Clark previously indicated it had evaluated outstanding litigation risks during its due diligence, the revived lawsuits may complicate that assessment as the acquisition moves toward completion.

The underlying scientific debate remains highly contested.

Several observational studies have suggested an association between prenatal acetaminophen exposure and developmental disorders. However, many medical organizations and researchers emphasize that association does not prove causation, noting that factors such as genetics, maternal illness, fever during pregnancy, environmental influences, and study limitations make it difficult to establish direct cause and effect.

Major health organizations continue advising pregnant women to consult their physicians before taking any medication, including acetaminophen, and generally recommend using the lowest effective dose for the shortest necessary period when treatment is medically appropriate.

The appellate ruling now returns the cases to Judge Denise Cote for additional proceedings. The district court will determine how the litigation moves forward, including renewed challenges to expert testimony and whether representative cases proceed toward trial.

Legal experts say Monday’s decision highlights the critical role expert scientific testimony plays in pharmaceutical litigation. Rather than resolving the underlying medical dispute, the appeals court determined that competing scientific opinions deserve to be weighed by juries instead of being dismissed before trial.

For Kenvue, the decision revives one of the company’s largest remaining legal challenges just as it seeks to complete a transformational merger. For the families bringing the lawsuits, it represents another opportunity to present their claims in court.

The litigation is expected to continue for years before any final resolution is reached.

This article discusses ongoing litigation. The court did not determine that acetaminophen causes autism or ADHD. Individuals with questions regarding medication use during pregnancy should consult their healthcare provider.

JBizNews Desk | New York
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