Rutledge v. Walgreen: The Second Circuit Clarifies the Line Between Gatekeeper and Decision-Maker

On July 13, in a precedential opinion, the United States Court of Appeals for the Second Circuit weighed in on the ongoing debate over how closely a district court may or should scrutinize a qualified expert’s opinions under Federal Rule of Evidence 702, as amended in 2023, and Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579 (1993).

In Rutledge v. Walgreen Co., arising from a multidistrict litigation concerning the alleged causal relationship between prenatal acetaminophen use and attention-deficit/hyperactivity disorder (ADHD) and/or autism spectrum disorder (ASD), the Second Circuit sought to limit overzealous gatekeeping, directing courts to “strike a middle-ground” between “the principle that a district court must take a hard look at the experts’ applications of accepted methods” and the principle that a “court cannot decide a Daubert motion based on its own judgment of an expert’s persuasiveness.”¹

The Second Circuit held that the district court went too far in excluding three of the plaintiffs’ experts, whose testimony was consistent with methodologies actually employed in their respective fields. In doing so, the circuit court found that the district court improperly substituted its own understanding of epidemiology for that of the scientists and excluded opinions that fell within the bounds of legitimate scientific debate.

Rutledge thus confirms that the 2023 amendment to Rule 702 did not represent a sea change in the governing expert-admissibility standards but clarifies and cautions that the district court’s gatekeeping role is, and always has been, to shield the jury from expert testimony that is outside the boundaries of legitimate scientific discourse. It is not, however, to decide which points in any given scientific debate are more persuasive.

The 2023 Amendment to Rule 702

As the Advisory Committee explained, in the years leading up to the amendment, “many courts” had erroneously “held that the critical questions of the sufficiency of an expert’s basis, and the application of the expert’s methodology, are questions of weight and not admissibility.”²

Effective December 1, 2023, Rule 702 was “amended to clarify and emphasize that expert testimony may not be admitted unless the proponent demonstrates to the court that it is more likely than not that the proffered testimony meets the admissibility requirements set forth in the rule.”³ The rule was also “amended to emphasize that each expert opinion must stay within the bounds of what can be concluded from a reliable application of the expert’s basis and methodology.”⁴

Difficult Terrain to Navigate

Both before and after the 2023 amendment, trial courts have struggled to determine how rigorously to scrutinize expert testimony, particularly when evaluating testimony concerning controversial or highly technical scientific issues.

During a recent oral argument in the multidistrict litigation involving Zantac heartburn medication, Eleventh Circuit Judge Adalberto Jordan observed that “the problem is that there’s been too much ink spilled” in this area of the law, and described it as “difficult terrain to navigate.”⁵ Judge Jordan later characterized the line between gatekeeper and decision-maker as “unintelligible.”⁶

At oral argument in Rutledge, Second Circuit Judge Gerard E. Lynch similarly observed that, as a judge, “you’re not supposed to play scientist, but you are supposed to take a hard look at what the scientists say.”⁷ He acknowledged that “the poor district judge has to walk a certain line there and hopefully we might be able to give some guidance there as to how to walk that line.”⁸ Rutledge represents the Second Circuit’s effort to provide that guidance.

The Court Reins In Overzealous Gatekeeping

In Rutledge and its companion case, Phippen v. Walgreen Co., children, parents, and guardians asserted state-law failure-to-warn claims against pharmaceutical companies, pharmacies, and retailers, alleging that prenatal ingestion of acetaminophen, the active ingredient in Tylenol and its generic equivalents, caused them or their children to develop ADHD and/or ASD.⁹

The Rutledge plaintiffs relied on five experts to establish a causal link. The district court excluded the testimony of all five experts as unreliable, reasoning that “the state of scientific evidence on prenatal use of acetaminophen presents a challenge for any expert witness offering the opinion that such use causes ADHD and ASD” and that “there is no generally accepted scientific conclusion that in utero exposure to acetaminophen causes either” condition.¹⁰

After emphasizing that it was not deciding whether acetaminophen in fact causes ADHD or ASD, the Second Circuit held that the district court overstepped its gatekeeping role by excluding three of the plaintiffs’ experts. The appellate court instead concluded that these experts “offered opinions that comport with methodologies applied by other scientists in their fields, and constitute acceptable interpretations of scientific evidence where scientists may, and in fact do, disagree on the ultimate answer to the causal question that they are assessing.”¹¹

The Second Circuit’s analysis focused primarily on Dr. Andrea Baccarelli, an epidemiologist, a physician, and dean of the Harvard T.H. Chan School of Public Health. Dr. Baccarelli performed a Bradford Hill analysis, a widely used method for assessing whether an observed association is causal in nature, and concluded that the available epidemiological evidence supports a finding of causality between prenatal acetaminophen exposure and ADHD and ASD. The Second Circuit found his methodology and its application sufficiently reliable for a jury to consider, reasoning that many of the district court’s criticisms went to the persuasiveness of Dr. Baccarelli’s conclusions rather than the admissibility of his testimony.

One example illustrates the line the court drew. Dr. Baccarelli evaluated ADHD and ASD together in a single Bradford Hill analysis rather than performing separate analyses for each condition. The district court found that approach unreliable, largely because ADHD and ASD have different diagnostic criteria.

The Second Circuit disagreed, concluding that Dr. Baccarelli adequately explained his methodological choice and that epidemiologists routinely employ the same methodology outside the context of litigation. Drawing a sharp distinction between admissibility and persuasiveness, the Second Circuit explained that “we do not conclude that we think the structure Baccarelli employed for his Bradford Hill analysis is the best one, nor do we have any prediction, one way or another, about whether a jury will find it persuasive.”¹² In the court’s view, Dr. Baccarelli’s “single, multiple-outcomes analysis may well prove unconvincing to a jury for precisely the reasons that the district court identifies, but that does not render the expert opinion excludable for the purposes of Rule 702.”¹³

The Second Circuit further rejected the district court’s accusation that Dr. Baccarelli engaged in cherry-picking—that is, selectively relying on evidence supporting a particular position while ignoring or discounting contrary evidence. “It is not cherry-picking,” the court explained, “for an expert to prefer one study to another when he offers a coherent, scientifically plausible reason for the preference.”¹⁴

Practical Takeaways

Rutledge is one of the first federal appellate decisions since Rule 702’s 2023 amendment to thoroughly address the question of when a court crosses the line from gatekeeper to scientific arbiter. Although binding only within the Second Circuit (Connecticut, New York, and Vermont), the decision will likely influence how courts across the country discharge their gatekeeping role under Rule 702 and Daubert.

The decision reinforces the importance of meaningful judicial gatekeeping while seeking to moderate a trend toward increasingly rigorous Rule 702 scrutiny following the 2023 amendment. With Rutledge, the Second Circuit sought to “strike a middle-ground.”

This approach may result in more expert testimony reaching juries, particularly in cases where qualified scientists reasonably disagree about the available evidence.

Under Rutledge, experts who offer controversial or even unpersuasive opinions may nevertheless survive a Rule 702 challenge if they (1) apply an established methodology in a manner consistent with others in the field, (2) fairly consider the relevant body of evidence without ignoring or misrepresenting contrary evidence, and (3) provide reasonable, scientifically grounded explanations for their conclusions.

Practitioners and clients should keep these principles in mind when selecting experts, conducting expert discovery, defending expert testimony, and challenging an opposing expert.

For guidance in navigating these complex Rule 702 and Daubert issues, please contact Lowenstein Sandler’s Litigation Department.

¹ Rutledge v. Walgreen Co., Nos. 24-916-cv(L), 24-1121(Con), 24-2360(Con), 24-2594-cv, slip op. at 44 n.25 (2d Cir. July 13, 2026).
² Fed. R. Evid. 702 Advisory Committee’s note to the 2023 amendment.
³ Id. (citing Fed. R. Evid. 104(a)).
⁴ Id.
⁵ Audio Recording of Oral Argument at 18:36–19:30, In re Zantac (Ranitidine) Prods. Liab. Litig., No. 21-12618 (11th Cir. Oct. 10, 2025).
⁶ Id. at 39:22–39:56.
⁷ Audio Recording of Oral Argument at 19:57–20:35, Rutledge v. Walgreen Co., Nos. 24-916-cv(L), 24-1121(Con), 24-2360(Con), 24-2594-cv (2d Cir. Nov. 17, 2025).
⁸ Id.
⁹ This alert does not separately address Phippen, because the Second Circuit vacated and remanded without deciding the admissibility of Dr. Ness’ testimony.
¹⁰ In re Acetaminophen—ASD-ADHD Prods. Liab. Litig., 707 F. Supp. 3d 309, 333–34 (S.D.N.Y. 2023).
¹¹ Rutledge, slip op. at 7.
¹² Id. at 33 (emphasis in original).
¹³ Id.
¹⁴ Id. at 40 (emphasis in original).