Product Liability & Mass Torts Digest

The December 18, 2023 Southern District of New York opinion In re Acetaminophen – ASD-ADHD Products Liability Litigation, notable for excluding all five of plaintiffs’ general causation experts under Federal Rule of Evidence 702, reaffirms the importance of the FDA’s conclusions on causation, along with those of other research and medical organizations.

The Southern District of New York’s recent opinion in the In re Acetaminophen MDL establishes strong guardrails regarding how expert witnesses can rely on studies and data in support of their opinions. By way of background, In re Acetaminophen involves more than 600 plaintiffs who allege that the manufacturer and retailers of acetaminophen products failed to warn that children may develop autism spectrum disorder (ASD) or attention-deficit hyperactivity disorder (ADHD) from in utero exposure to the drug. In an opinion issued on December 18, 2023, Judge Denise Cote of the Southern District of New York excluded all five of the plaintiffs’ general causation experts as unreliable.

A Bradford Hill analysis—a set of criteria first proposed by the British epidemiologist Sir Austin Bradford Hill in 1965 to evaluate the strength of evidence for a causal relationship between two variables[1]—often plays a critical role in causation opinions of plaintiff experts in product liability matters. 

A recent and thorough opinion in In re Acetaminophen – ASD-ADHD Products Liability Litigation reaffirms the need for parties’ general causation experts to meaningfully engage with known confounding factors to ensure the admissibility of their opinions.