2nd Circuit revives wave of acetaminophen lawsuits alleging link to ADHD and autism

A federal appeals court on Monday revived hundreds of lawsuits in which plaintiffs alleged that use of acetaminophen, the active ingredient in products such as Tylenol, can lead to neurodevelopmental disorders including ADHD and autism. The decision came from the U.S. Court of Appeals for the 2nd Circuit.

According to The Hill, the appeals court said a lower court improperly threw out testimony from scientific experts that plaintiffs argued provided evidence of a link between the pain reliever and pregnancy-related harms. The 2nd Circuit’s ruling, as described by the outlet, means the cases that had been dismissed at the trial level will move forward again.

The lawsuits were brought by plaintiffs who claimed they have evidence that acetaminophen exposure during pregnancy is associated with outcomes involving ADHD and autism. The core dispute in the litigation, as reflected in Monday’s appellate outcome, centered in part on whether the scientific expert testimony offered by plaintiffs should have been admitted in the lower court proceedings.

In its reversal, the 2nd Circuit addressed the admissibility approach taken by the district court, The Hill reported, concluding that the exclusion of expert evidence was not appropriate. By reinstating the cases, the appeals court effectively reopened a procedural path for plaintiffs to pursue their claims and for defendants to respond to the expert evidence at later stages of the litigation.

While the ruling does not itself resolve whether acetaminophen causes ADHD or autism, it changes the litigation posture for a large number of pending suits. The practical effect is to restore claims that had been blocked, potentially increasing legal costs for both sides and extending timelines for discovery and further motions.

The next steps will depend on how the reinstated cases are handled in the district courts, including whether there are renewed disputes over expert testimony, the scope of permitted scientific evidence, and the applicable legal standards for causation and damages. The appellate ruling also leaves room for defendants to continue challenging the scientific basis for plaintiffs’ allegations through the remaining stages of litigation.