In Beavan v. Allergan U.S.A., Inc., decided May 27, 2026, a unanimous New Jersey Supreme Court clarified two of the most important evidentiary rules in product liability litigation: the requirement that any designated causation expert, including a treating physician, serve a written report, and the rigorous gatekeeping of differential diagnosis opinions under In re Accutane Litigation.
Background
The plaintiff alleged she lost vision in one eye after an injection of Ozurdex, a steroid implant manufactured by Allergan, drawn from a recalled lot that potentially contained silicone particulates. She had a documented history of preexisting eye conditions. On causation, she offered two witnesses: a retained ophthalmologist who served a written report relying on a differential diagnosis methodology, and her treating physician, whom she designated to give causation opinions without ever serving a report of his opinions.
The Decision
The Court held that a physician designated to provide expert testimony on causation must serve a written report setting forth those opinions, even if the physician is a treater rather than a retained litigation expert. Treating status does not exempt a witness from the disclosure obligations of Rule 4:17-4(e), and an adversary is entitled to move to bar undisclosed causation opinions.
The Court further held that the admissibility of the retained expert's differential diagnosis opinion must be governed by the rigorous gatekeeping analysis prescribed in In re Accutane Litigation. A differential diagnosis is only as reliable as the expert's process for ruling in the alleged product cause and ruling out alternative explanations, and trial courts must actually test that methodology rather than wave it through to the jury.
What It Means for New Jersey Cases
Treating physicians have long served as de facto causation experts in pharmaceutical, medical device, and general product cases, in part because juries find them credible and in part because some courts tolerated their testifying without reports. Beavan ends that practice: any party intending to elicit causation opinions from a treater must disclose those opinions in a written report, and any party facing an undisclosed opinion has clear authority to bar it. The decision also confirms that the gatekeeping standard New Jersey courts apply to methodology-based causation opinions is a demanding one, particularly where a preexisting condition offers an alternative explanation for the injury.
Beavan also works hand in glove with New Jersey's net opinion doctrine. An expert who cannot articulate why the product, rather than the plaintiff's documented history, caused the injury is vulnerable on two independent grounds: unreliable methodology under Accutane and a bare conclusion under the net opinion rule. The same principles cut in every direction; an expert retained by any party faces the identical scrutiny.
How We Put It to Work
We audit every expert designation in our product and injury files against Beavan. Where a treating physician has been designated for causation without a report, the testimony is subject to a motion to bar rather than mere cross-examination, and where our own witnesses will offer causation opinions, we make sure the disclosure record is airtight. Where an expert relies on differential diagnosis, we evaluate whether a Rule 104 hearing is warranted and build the record of alternative causes, using treatment records, prior conditions, and competing risk factors. In cases like Beavan itself, where the medical history supplies alternative explanations, the causation case can be won or lost on expert-discovery practice long before trial.
This article is provided for general informational purposes only and does not constitute legal advice. Reading it does not create an attorney-client relationship with Sanchez Maselli Trial Attorneys.