by Eddie Ruiz
The Tylenol/acetaminophen case before the Second Circuit involved consolidated failure to warn claims brought by parents, guardians and children who alleged that prenatal exposure to acetaminophen, the active ingredient in Tylenol and many generic pain relievers, caused children to develop ADHD and/or autism spectrum disorder.
The defendants included manufacturers, pharmacies and retailers involved in making, marketing or selling acetaminophen products. The court emphasized at the outset that the appeal was not about deciding whether acetaminophen actually causes ADHD or ASD, nor whether warnings must ultimately be added.
Instead, the appeal concerned whether the plaintiffs’ expert testimony was admissible under the rules governing scientific evidence.
Understanding the Second Circuit Appeal
The scientific background was central to the dispute. Acetaminophen is commonly used during pregnancy for pain and fever, and it can cross the placental barrier into fetal circulation. Existing FDA-required labeling tells pregnant or breastfeeding consumers to consult a health professional before use, but it does not require a specific ADHD or ASD warning.
The Second Circuit noted that scientists have studied possible links between prenatal acetaminophen exposure and neurodevelopmental disorders for years, but no study has definitively established causation. FDA reviews had recognized associations in some studies while also pointing to limitations and inconsistent results that prevented a firm causation finding.
The cases came from multidistrict litigation (MDL), a procedure that allows similar federal lawsuits to be managed together before one judge, in the Southern District of New York. The plaintiffs first had to prove “general causation,” meaning that prenatal acetaminophen exposure is capable of causing ADHD and/or ASD in the general population before addressing whether it caused injuries to any individual plaintiff.
The plaintiffs offered multiple experts, including:
- Dr. Andrea Baccarelli
- Dr. Eric Hollander
- Dr. Brandon Pearson
- Dr. Robert Cabrera
- Dr. Stan Louie
The district court excluded all five experts[1] under Rule 702 and Daubert, finding their causation opinions unreliable, and then granted summary judgment for the defendants in roughly 550 cases.
Why the Second Circuit Reversed Part of the District Court’s Decision
On appeal, the Second Circuit[2] partly disagreed with the district court. It held that the district court exceeded its gatekeeping role by excluding the testimony of Drs. Baccarelli, Hollander and Pearson.
According to the appellate court, those experts used accepted scientific methodologies and offered interpretations that fell within the range of reasonable scientific disagreement. The Second Circuit stressed that a judge’s role under Daubert is to screen out unreliable or “junk” science, not to decide which side of an ongoing scientific debate is ultimately more persuasive.
Kenvue’s public response to the Second Circuit’s ruling attempts to minimize the decision by describing it as merely procedural and “not about the science.” That framing is questionable. While the Second Circuit did not decide whether acetaminophen causes ADHD or autism, the appeal was very much about whether the plaintiffs’ scientific evidence was reliable enough to be heard.
The court found that the opinions of key plaintiffs’ experts belonged before a jury rather than being discarded at the gatekeeping stage. Likewise, Kenvue’s statement that “current scientific evidence does not support a causal relationship” presents the scientific question as settled.
The Second Circuit described it differently as an area of ongoing scientific debate. The court did not hold that plaintiffs are right on causation, but it rejected the notion that their key expert opinions were so unreliable that no jury should hear them.
The Court Clarifies the Role of Expert Testimony
The court gave particular attention to Dr. Baccarelli’s use of the Bradford Hill criteria, a common epidemiological framework for evaluating causation. The district court had faulted his analysis for issues such as:
- Dose response evidence
- Biological plausibility
- Specificity
- Alleged cherry picking
The Second Circuit found that the district court substituted its own view of epidemiological requirements for the views of experts in the field and treated contested scientific questions as though they had only one permissible interpretation.
The appellate court made clear that when qualified experts reliably apply accepted methods to disputed scientific evidence, the jury, not the judge, usually decides how much weight to give that testimony.
Not Every Expert Was Reinstated
The Second Circuit did not accept all of the plaintiffs’ expert evidence. It affirmed the exclusion of Dr. Cabrera and Dr. Louie. As for Dr. Cabrera, the court held that the district court acted within its discretion because his Bradford Hill analysis did not adequately weigh or synthesize the relevant factors.
The court agreed that Dr. Louie, who opined about a 28 day exposure threshold during pregnancy, had not sufficiently explained how he reached that conclusion from the studies he reviewed and had mischaracterized certain evidence.
The court also addressed the related Phippen appeal, which involved plaintiffs alleging ADHD-only injuries and an additional expert, Dr. Roberta Ness. Because the Second Circuit reinstated the admissibility of key Rutledge experts, it vacated the judgment in Phippen and remanded for further proceedings, leaving the district court to reconsider whether Dr. Ness’s testimony remained necessary or admissible in light of the appellate ruling.
What the Decision Means Going Forward
That reasoning also weakens Kenvue’s suggestion that it should now receive a fresh opportunity to exclude the plaintiffs’ key causation experts. In response to the ruling, Kenvue said, “We now have another opportunity to show that the plaintiffs’ experts’ opinions are unreliable and should not be allowed.”[3]
The Second Circuit has already concluded that the district court wrongly kept three of those experts from the jury, and that ruling meaningfully changes the posture of the litigation. Kenvue remains free to challenge causation on the merits, cross examine the experts and present competing scientific evidence. But the appellate decision gives plaintiffs renewed momentum by restoring important expert testimony that may allow their failure-to-warn claims to proceed beyond the threshold admissibility stage.
Ruth Rizkalla, an attorney at The Carlson Law Firm who previously served on the plaintiffs' leadership committee in the Tylenol litigation, said the Second Circuit's decision could have significant implications for future Tylenol autism and ADHD claims.
“The Second Circuit’s decision acknowledges that plaintiffs’ experts have a sound basis to testify about the alleged causal connection between prenatal Tylenol use and an increased likelihood of children developing autism spectrum disorder and/or with attention deficit/hyperactivity disorder,” said Rizkalla. “This decision allows mothers and their children to move forward with their claims against the makers of Tylenol, as well as other related defendants.”
The Second Circuit rejected the defendants’ alternative argument that federal drug labeling law preempted the plaintiffs’ state law failure to warn claims. The court agreed with the district court that, although federal regulations require a general pregnancy warning for acetaminophen products, they do not necessarily bar manufacturers from adding a more specific warning about plausible risks such as ADHD or ASD.
By vacating the judgments and remanding the cases, the Second Circuit did not decide whether Tylenol causes ADHD or autism. However, it did reopen the courthouse door for plaintiffs to test their evidence before a jury and continue seeking answers about what risks, if any, prenatal acetaminophen exposure may pose.
What This Means for Tylenol Plaintiffs
The Second Circuit's decision does not determine whether prenatal acetaminophen exposure causes ADHD or autism. Instead, it confirms that key expert testimony may be presented to a jury, allowing the litigation to move forward.
The Carlson Law Firm will continue monitoring developments in the Tylenol lawsuit and providing updates on important dangerous drug litigation. If you have questions about the Tylenol lawsuits or believe your family may have been affected, contact our attorneys to learn more about your legal options.
[1] In re Acetaminophen – ASD-ADHD Prods. Liab. Litig., 707 F. Supp. 3d 309 (S.D.N.Y. 2023)
[2] Rutledge v. Walgreen Co., Nos. 24-916-cv(L), 24-1121 (Con.), 24-2360 (Con.), 24-2594-cv (2d Cir. July 13, 2026).
[3] Id
