Tylenol MDL Judge Rejects New Evidence That Prenatal Exposure to Acetaminophen Causes ADHD

Drug manufacturers and retailers successfully challenged the scientific approaches used by another plaintiffs expert proposed to establish a link between prenatal use of the ingredient in Tylenol and ADHD.

The U.S. District Judge presiding over all Tylenol ADHD and autism lawsuits has again rejected a critical plaintiffs’ expert witness, leaving them without a way to provide admissible testimony to support claims that use of acetaminophen during pregnancy can cause attention-deficit hyperactivity disorder (ADHD) among children.

For decades, Tylenol (acetaminophen) has been widely used by pregnant women, largely due to the widespread belief that it is safe for unborn children. However, a growing number of lawsuits have been filed in state and federal courts in recent years, each raising similar allegations that drug makers failed to adequately warn pregnant women and the medical community about the growing evidence that prenatal exposure to Tylenol causes autism or ADHD.

Given common questions of fact and law raised in lawsuits brought throughout the federal court system over the adequacy of the Tylenol pregnancy warnings, the U.S. Judicial Panel on Multidistrict Litigation (JPML) established coordinated pretrial proceedings, centralizing all claims before U.S. District Judge Denise Cote in the Southern District of New York, as part of a federal multidistrict litigation (MDL).

In December 2023, Judge Cote issued a controversial opinion excluding plaintiffs’ expert witnesses from testifying about the Tylenol pregnancy side effects, after determining the scientific approaches and studies used were not sound enough to allow the opinions to be presented to a jury.

The move has been seen as spelling the end of the Tylenol litigation in the federal court system, since it left plaintiffs without required expert testimony to prove Tylenol caused developmental disorders when women took the painkiller during pregnancy. However, families who filed their lawsuits after the date of the original order argued that they should be allowed to present new evidence.

Another Tylenol Expert Witness Rejected

In March, Judge Cote issued a court order allowing plaintiffs who filed Tylenol ADHD lawsuits after January 12, known as the Mota plaintiffs, to present arguments to the court on whether Dr. Roberta B. Ness could serve as an expert witness to establish causation in those cases.

Defendants objected to the use of Dr. Ness, questioning her experience and the evidence she has used to conclude prenatal exposure to acetaminophen causes ADHD or autism. In an opinion (PDF) issued on July 10, Judge Cote agreed, ruling that Dr. Ness could not speak before juries on Tylenol ADHD and autism causation.

“To be sure, given the state of the science Dr. Ness confronted long odds in offering her opinion on causation. ADHD can be a serious disorder, and scientists have sought to understand its origins. It is now estimated to be approximately 74% heritable,” Judge Cote wrote. “Many potential linkages to ADHD have been studied, among them the potential association between ADHD and prenatal exposure to acetaminophen. Dr. Ness acknowledges that the evidence of any association between prenatal exposure to acetaminophen and an ADHD diagnosis in offspring is only ‘modest’.”

The ruling again leaves these new plaintiffs without a means of proving causation, meaning additional Tylenol ADHD and autism lawsuits brought in the federal court system this year will likely be dismissed. However, the ruling does not apply to lawsuits filed in various state courts nationwide, which have different evidentiary standards and are continuing to be pursued by lawyers.