Court weighs expert evidence in the GLP-1 stomach injury MDL

The largest US lawsuit group over GLP-1 medications reaches its biggest test this month. A hearing on whether plaintiffs' expert scientific testimony is admissible under Federal Rule of Evidence 702 was set for mid-September 2026 in MDL 3094, the multidistrict litigation over claims that drugs including semaglutide caused gastroparesis (sometimes called stomach paralysis), intestinal obstruction and ileus ^[1].

Litigation trackers list the hearing window differently — one law firm page gives September 14–18, 2026 ^[1], while other trackers have described a September 10–18 window. The exact start date has not been confirmed against the court docket, and the discrepancy has not been resolved in the available sources.

What is actually being decided

Rule 702 governs whether a jury ever hears from an expert witness. In pharmaceutical litigation, that usually means deciding whether plaintiffs' experts have a reliable scientific basis for saying a drug can cause a particular injury. If key experts are excluded, cases often collapse. If they survive, the litigation moves toward bellwether trials — test cases that help both sides gauge the value of the rest.

MDL 3094 was created on February 2, 2024, and sits before Judge Karen S. Marston in the Eastern District of Pennsylvania ^[1]. As of the August 2026 report from the Judicial Panel on Multidistrict Litigation, 3,928 stomach-injury cases were consolidated there ^[1]. A second, newer MDL — 3163, covering claims of NAION vision loss — was created December 15, 2025 before the same judge and had grown to about 200 cases ^[1].

The defense has already won significant rulings. In August 2025, the court excluded two of the plaintiffs' diagnostic experts and held that gastroparesis claims must be backed by an objective gastric emptying study ^[1]. Design-defect theories have been narrowed, leaving the litigation primarily a failure-to-warn case — the argument that drug labels did not adequately describe the risk ^[1]. The governing pleading is a 264-page Amended Master Long Form Complaint filed August 29, 2025, containing sixteen counts, including negligence and strict-liability failure to warn, warranty claims, and fraud and misrepresentation claims ^[1]. The manufacturers dispute the allegations, and none have been proven ^[1].

It is worth knowing where these numbers come from. The case counts and hearing dates above are drawn from a plaintiffs' law firm page that is explicitly labeled attorney advertising and that is actively recruiting clients ^[1]. A second tracker source could not be retrieved for this story.

Why it matters for patients

Nothing about this hearing is a regulatory finding. As of the most recent update available, no GLP-1 lawsuit has settled, no jury has returned a verdict, and no court has found that these medications caused anyone's injury ^[1]. A courtroom ruling on expert testimony is a legal judgment about whether specific witnesses meet an evidentiary standard — it is not the same as FDA action, a label change, or a new safety warning.

For people taking semaglutide (Ozempic, Wegovy, Rybelsus) or tirzepatide (Mounjaro, Zepbound), the practical takeaway is that gastrointestinal effects remain the most discussed safety question in this litigation, and the courts are still sorting out what the science shows. Gastrointestinal side effects are already well documented in these drugs' labeling; what is contested is whether severe, persistent injuries such as gastroparesis were adequately disclosed.

For anyone who has filed or is considering a claim, the August 2025 gastric emptying study requirement is the concrete filter that has already reshaped who can proceed ^[1]. The eligibility criteria one firm describes — brand-name use, objective testing, an ER visit or hospital admission, and a diagnosis before December 31, 2024 — are that firm's intake screen, not a court-wide rule ^[1].

What happens next

The hearing itself is expected to run several days in mid-September 2026 ^[1]. A written ruling typically follows weeks or months later; no decision date has been announced in the available sources. There is currently no trial date in MDL 3094 ^[1].

The NAION track in MDL 3163 is younger, with no dismissals reported so far and no expert-evidence testing yet ^[1]. European regulators added NAION to semaglutide labeling as a "very rare" side effect in June 2025, following a 2024 Harvard study reporting elevated risk ^[1]. How US courts treat that evidence remains unknown.