Litigation Before Validation: When Courtrooms Outpace Science

published June 11, 2025

Inside the Acetaminophen Litigation Battleground

This article is Part III of a five-part series, “Acetaminophen at the Intersection,” exploring how this controversy demonstrates the critical need for rigorous analysis at the crossroads of science, justice, and economics.

On December 18, 2023, U.S. District Judge Denise Cote faced a pivotal decision in a national legal battle: could the scientific evidence linking prenatal acetaminophen exposure to autism and ADHD withstand judicial scrutiny? The hearing represented a critical moment in Multidistrict Litigation 3043, which had grown to encompass approximately 500 lawsuits against Kenvue (formerly part of Johnson & Johnson) and major national retailers. At stake was whether observational studies showing modest 20-30% risk increases would prevail against a landmark Swedish sibling-comparison study of 2.4 million births that found no causal relationship once familial factors were controlled. Applying the Daubert standard for scientific testimony, Judge Cote ultimately excluded all five plaintiffs’ causation experts, finding their methodologies unreliable. With no admissible evidence on causation, she granted summary judgment to the defendants—effectively halting the federal cases while reshaping the trajectory of parallel state-court litigation [1][2][4].

Anatomy of a Mass Tort

Unlike class actions where all claimants share a single settlement pool, mass-tort litigation allows plaintiffs to maintain individual damage claims while coordinating pre-trial procedures to increase efficiency and reduce costs. In October 2022, the Judicial Panel on Multidistrict Litigation consolidated fewer than twenty acetaminophen lawsuits into MDL 3043; within a year, the case inventory had expanded more than twenty-fold to over 500 cases [3].

These cases shared a common allegation: manufacturers and retailers failed to warn pregnant women that prenatal acetaminophen exposure may increase neurodevelopmental risks in their children. The financial stakes were substantial—plaintiffs sought compensation for estimated lifetime costs that can exceed $2 million per child with autism spectrum disorder, a figure consistent with health economics research on the lifetime burden of care, educational support, and diminished earning capacity [8].

Science on the Witness Stand

To prevail in product liability litigation, plaintiffs must clear the evidentiary threshold established in Federal Rule 702: expert opinions must utilize reliable methods, not merely impressive credentials. The plaintiffs’ legal team recruited prominent scientists including epidemiologist Andrea Baccarelli who cited meta-analyses demonstrating statistical associations between prenatal acetaminophen exposure and subsequent ADHD or autism diagnoses, with effect sizes typically showing 20-30% increased relative risk [6].

Defense attorneys countered by highlighting the methodological limitations of these studies, particularly emphasizing the landmark Swedish sibling-comparison study involving 2.4 million births that found no association once shared genetics and family environment were properly controlled [2]. After extensive briefing and hearings, Judge Cote issued a detailed opinion finding the plaintiffs’ experts had employed “results-driven” approaches, specifically citing their selective reliance on certain biomarker studies while minimizing contrary evidence, inadequate consideration of genetic confounding, and drawing stronger conclusions than the underlying data justified [1][2].

The court’s ruling resulted in the exclusion of all five plaintiffs’ general causation experts—a decisive application of the judiciary’s gatekeeping function under Daubert that effectively prevented the litigation from proceeding to trial [1][4].

When Gatekeeping Works

Judge Cote’s ruling exemplifies why courts, rather than juries, are tasked with evaluating scientific methodology. Her opinion articulated a four-part reliability framework that has potential implications beyond acetaminophen litigation:

Transparent data selection — Expert analysis must clearly define and justify which studies are included or excluded from consideration
Objective causation framework — Established methodologies like Bradford Hill criteria must be applied systematically rather than selectively
Robust confounder control — Analysis must adequately account for crucial factors like genetics, maternal fever, and socioeconomic variables
Alignment with scientific consensus — Expert opinions should accurately reflect the state of knowledge as represented by regulatory bodies and professional organizations

With no admissible evidence to establish general causation—the threshold question of whether acetaminophen can cause the claimed injuries at all—the court granted summary judgment to defendants, an outcome that substantially reduced projected liability exposure and prompted a notable increase in Kenvue’s stock price [1].

Jurisdiction Shopping: The Move to State Courts

While the federal MDL dismissal represented a significant victory for defendants, it did not close the litigation chapter entirely. State-court proceedings in California, Illinois, and Pennsylvania continue under varying evidentiary standards—some potentially less stringent than the federal Daubert rule. Plaintiffs’ attorneys have also indicated they will appeal Judge Cote’s rulings, arguing she overstepped her gatekeeping role by evaluating the credibility of the experts rather than merely assessing their methodologies.

Meanwhile, defendants have invoked federal preemption arguments, contending that any required over-the-counter label changes would need FDA approval, potentially shielding them from state-law failure-to-warn claims. This complex jurisdictional landscape creates the possibility of divergent outcomes across venues—a scenario where seemingly identical scientific evidence could lead to dismissal in federal court but jury trials in certain states. Such inconsistency raises important questions about whether scientific evidence should be evaluated differently based solely on jurisdiction.

In Plain English

Hundreds of families have filed lawsuits against retailers and acetaminophen manufacturers, claiming that prenatal use of the medication caused autism or ADHD in their children. A federal judge in New York dismissed these cases after finding that the scientific experts failed to use reliable methods—particularly by not adequately accounting for genetic factors and other potential explanations. While this federal ruling is significant, similar lawsuits continue in state courts where different evidence rules apply. The litigation highlights how judges serve as scientific gatekeepers in our legal system, evaluating the reliability of expert testimony before cases reach a jury.

Myth vs. Reality

Myth: Courts primarily focus on corporate misconduct rather than scientific validity.
Reality: To succeed in litigation, plaintiffs must establish medical causation through scientifically reliable evidence that meets judicial standards [1][4].
Myth: A single concerning study is sufficient justification for a warning label.
Reality: FDA and major obstetric professional organizations require a consistent body of evidence before modifying clinical guidance [7].
Myth: Any expert with advanced degrees and publications can testify in court.
Reality: Judges must exclude even highly credentialed experts who fail to apply reliable scientific methods or who disregard alternative explanations [1][4].
Myth: The federal MDL dismissal conclusively resolves the acetaminophen litigation.
Reality: State court proceedings and potential appellate decisions mean the scientific and legal questions remain active in multiple forums.

Key Takeaway

The acetaminophen litigation demonstrates that in complex scientific cases, methodological rigor rather than courtroom persuasion ultimately determines whether alleged health risks reach a jury—a principle that protects both scientific integrity and judicial fairness.

Coming Next

In Part IV, “The Ripple Effect: How Scientific Uncertainty Creates Real-World Costs,” we’ll examine the economic and healthcare implications of prolonged scientific ambiguity and how litigation-driven decision-making affects patients, providers, and markets.