US Second Circuit revives more than 500 lawsuits against Tylenol maker Kenvue over alleged autism and ADHD link to acetaminophen
The US Second Circuit Court of Appeals in Manhattan has reinstated more than 500 product liability lawsuits against Kenvue, the maker of Tylenol, after ruling that a lower court improperly excluded expert testimony from three doctors who alleged a link between acetaminophen (the active ingredient in Tylenol) use during pregnancy and autism spectrum disorder or ADHD in children. In a 64-page decision, Circuit Judge Guido Calabresi held that the testimony of three expert witnesses, including the dean of Harvard University's School of Public Health, Andrea Baccarelli, reflected methodologies accepted by other scientists and constituted acceptable interpretations of contested scientific evidence. The appellate court stressed it was not ruling on whether acetaminophen causes autism or ADHD, only on the admissibility of the expert evidence. The cases were originally dismissed in December 2024 by US District Judge Denise Cote in Manhattan, who had criticised the plaintiffs' experts' methodology. The decision returns all cases to Judge Cote for further proceedings. Many retailers, including CVS, Kroger, Target, Walgreens, and Walmart, are also named as defendants. Kenvue maintained that Tylenol is safe and that credible independent science shows no proven causal link. Kenvue shares fell 1.8% and Kimberly-Clark (which agreed to acquire Kenvue for more than $40bn last November) shares fell 2.7% on the day of the ruling.
Why this matters
The reinstatement of more than 500 product liability claims is a significant litigation development with direct financial exposure implications for Kenvue and, through the pending Kimberly-Clark acquisition, for that transaction's risk profile. The Second Circuit's ruling on expert admissibility turns on the Daubert standard (the US framework governing the admissibility of scientific expert evidence), and the court's finding that contested but methodologically accepted scientific testimony cannot be excluded outright will shape how mass tort product liability cases involving contested epidemiological evidence proceed in federal courts. The 1.8% share price fall in Kenvue and 2.7% fall in Kimberly-Clark on the ruling day indicate the market's assessment of the increased litigation liability. For UK-trained lawyers, the case is a useful comparator to English product liability law and the admissibility of expert evidence under Civil Procedure Rules.
On the Ground
A trainee supporting the defendant in a product liability matter of this kind would assist with disclosure review and categorisation of documents relating to internal safety assessments, prepare sections of the chronology of regulatory and scientific developments concerning the product, and help compile witness statement bundles for expert witnesses.
Interview prep
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“How might the reinstatement of these product liability claims affect the terms and risk allocation of Kimberly-Clark's pending acquisition of Kenvue?”
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