Appeals Court Revives Tylenol Autism Lawsuits
A U.S. federal appeals court has revived more than 500 product liability lawsuits alleging that prenatal use of Tylenol (acetaminophen) may be linked to autism spectrum disorder (ASD) and attention-deficit/hyperactivity disorder (ADHD) in children. The decision by the 2nd U.S. Circuit Court of Appeals overturns a lower court ruling that had dismissed the cases after excluding key expert testimony offered by the plaintiffs. The appellate ruling does not determine whether Tylenol causes autism or ADHD. Instead, it concludes that the trial judge improperly excluded portions of the plaintiffs’ scientific evidence, allowing the lawsuits to move forward for further proceedings.
The litigation began after hundreds of families sued Kenvue, the current maker of Tylenol, along with retailers including CVS, Walmart, and Target, alleging they failed to warn pregnant consumers about potential neurodevelopmental risks associated with acetaminophen use during pregnancy. Plaintiffs argue that manufacturers knew or should have known of research suggesting a possible association between prolonged prenatal exposure to acetaminophen and developmental disorders such as autism and ADHD but failed to update product warnings accordingly. The defendants deny these allegations, maintaining that the available scientific evidence does not establish a causal relationship between prenatal acetaminophen use and either condition.
The lawsuits were previously consolidated into a multidistrict litigation (MDL) before U.S. District Judge Denise Cote in New York. In 2024, Judge Cote dismissed the cases after excluding testimony from five expert witnesses presented by the plaintiffs. She found that the experts’ methodologies failed to satisfy the reliability standards required under federal evidence rules established by the U.S. Supreme Court’s Daubert framework. Without admissible expert testimony establishing general causation, the plaintiffs could not proceed, leading to summary judgment in favor of the defendants.
The Second Circuit unanimously disagreed with portions of that decision. The appellate court ruled that Judge Cote applied an overly restrictive analysis when excluding three of the plaintiffs’ expert witnesses, including Harvard School of Public Health Dean Andrea Baccarelli. The appeals court determined that disagreements among scientists regarding the interpretation of medical studies generally go to the weight of the evidence rather than its admissibility. As a result, the panel concluded that juries—not judges—should evaluate competing expert opinions where accepted scientific methodologies have been employed, even if the scientific community remains divided on the ultimate conclusions. The appellate court, however, upheld the exclusion of two other expert witnesses whose methodologies were found insufficient.
Importantly, the appeals court emphasized that its ruling does not establish that Tylenol causes autism or ADHD. Instead, it merely restores the plaintiffs’ opportunity to present certain expert testimony before the district court. Numerous medical organizations continue to maintain that current scientific evidence does not prove a causal relationship between acetaminophen use during pregnancy and neurodevelopmental disorders. Acetaminophen remains one of the most commonly recommended pain relievers during pregnancy when used as directed, although healthcare providers generally advise taking the lowest effective dose for the shortest necessary duration.
Kenvue responded by reaffirming its confidence in Tylenol’s safety profile, stating that decades of research and regulatory reviews support the product’s safety when used appropriately. The company indicated it would continue challenging the plaintiffs’ expert testimony when the litigation returns to the district court. Kenvue also noted that numerous health authorities worldwide continue to recognize acetaminophen as an appropriate option for treating pain and fever during pregnancy under medical guidance.
The appellate ruling is expected to reinvigorate one of the largest pharmaceutical product liability proceedings in recent years. By reviving more than 500 lawsuits, the decision may encourage additional claims from families alleging similar injuries. Legal observers note that the case could significantly influence how courts evaluate scientific expert testimony in complex pharmaceutical litigation, particularly where epidemiological research remains contested rather than conclusive. The ruling also illustrates the judiciary’s careful distinction between determining whether expert opinions are sufficiently reliable to be heard by a jury and deciding whether those opinions ultimately prove causation.
Beyond this litigation, the case highlights the ongoing challenge courts face when balancing evolving scientific research with legal standards governing expert evidence. Product liability lawsuits involving pharmaceuticals frequently depend on competing interpretations of complex medical studies, requiring judges to determine whether scientific disagreements should prevent cases from reaching juries. The Second Circuit’s decision suggests that, where qualified experts rely on accepted methodologies, factual disputes may be more appropriately resolved through trial rather than dismissal at the preliminary stage.
As the litigation returns to the district court, plaintiffs will now have another opportunity to present their claims, while defendants will continue disputing both the scientific evidence and legal theories underlying the lawsuits. Although the appeals court has reopened the litigation, the plaintiffs must still prove at trial that prenatal acetaminophen exposure caused the alleged injuries and that manufacturers failed to provide legally adequate warnings. The ultimate outcome could have significant implications for pharmaceutical manufacturers, product labeling requirements, and future toxic tort litigation involving emerging scientific evidence.
Key Legal Outcome
- The 2nd U.S. Circuit Court of Appeals revived more than 500 private lawsuits linking prenatal Tylenol use to autism and ADHD.
- The court ruled that the district judge improperly excluded testimony from three expert witnesses, allowing the cases to proceed.
- The appellate court upheld the exclusion of two other expert witnesses whose methodologies were found unreliable.
- The lawsuits return to the district court for further proceedings rather than being dismissed.
- The ruling concerns the admissibility of expert evidence and does not determine that Tylenol causes autism or ADHD.
Why It Matters
- The ruling revives one of the largest pharmaceutical product liability litigations in the United States.
- It clarifies how courts may evaluate expert scientific testimony under the Daubert standard.
- The decision could influence future lawsuits involving disputed medical research and product warnings.
- Pharmaceutical companies may face renewed litigation over alleged failures to warn consumers of potential risks.
- The case highlights the distinction between allowing expert testimony at trial and proving medical causation.
