Judge Marston hears competing science on GLP-1 vision-loss claims in MDL 3163
A federal judge heard dueling expert presentations on whether GLP-1 drugs cause a sudden form of vision loss, a step that comes before any trial schedule is set.
Judge Karen S. Marston convened a Science Day in MDL 3163 on June 2, 2026, hearing competing scientific accounts of whether GLP-1 medications can cause non-arteritic anterior ischemic optic neuropathy (NAION), a sudden form of vision loss [1][2][3]. The session is educational rather than a ruling; nothing was decided [1].
MDL 3163 was created on December 15, 2025 by the Judicial Panel on Multidistrict Litigation to consolidate federal NAION claims against Novo Nordisk and Eli Lilly in the Eastern District of Pennsylvania [1][3]. It is separate from MDL 3094, the older and much larger litigation over gastrointestinal injuries, which had 3,763 pending cases as of the June 1, 2026 JPML report [1]. MDL 3163 had 110 pending cases on the same report, up from 86 in May [1][3]. A separately maintained page reports 216 cases by September 2026, reflecting growth after the June 1 count [3].
The drugs at issue are described differently in the two trackers. One lists Ozempic, Wegovy, and Saxenda (Novo Nordisk) and Trulicity (Eli Lilly) [1]. The other lists Novo Nordisk's Ozempic, Wegovy, and Rybelsus and Eli Lilly's Mounjaro and Zepbound, noting that tirzepatide is a dual GIP/GLP-1 agonist rather than a pure GLP-1 [3].
The scientific dispute involves studies with different designs and results. A July 2024 study from Massachusetts Eye and Ear, published in JAMA Ophthalmology, followed 16,827 patients and reported higher NAION risk in people prescribed semaglutide: 4.28 times higher for patients with type 2 diabetes (8.9% versus 1.8% cumulative incidence) and 7.64 times higher for patients using it for weight loss (6.7% versus 0.8%) [3]. A February 2025 study of 37.1 million patients found a modest but elevated risk, with an incidence rate ratio of 1.32 [3]. A Danish-Norwegian study of more than 424,000 patients reported 2.19 times higher risk compared with SGLT2 inhibitors [3].
Regulators have split. In June 2025, the European Medicines Agency's pharmacovigilance committee concluded that NAION is a "very rare" side effect of semaglutide and recommended adding it to European labels [3]. NAION does not appear on U.S. labels for Ozempic, Wegovy, or Rybelsus as of March 2026, and the FDA is reportedly evaluating whether to act [3]. Plaintiffs' failure-to-warn claims center on that gap [3].
NAION is typically sudden and painless, often noticed on waking. It usually affects one eye and can affect the second in 15% to 25% of cases over five years; vision loss is usually permanent, and no effective treatment exists, according to one source [3]. It affects roughly 21,000 Americans a year [3]. Known risk factors include diabetes, high blood pressure, sleep apnea, certain optic disc anatomy, and age over 50 — conditions common among GLP-1 users, which defendants cite as possible confounders [3]. Proposed mechanisms under investigation include rapid metabolic changes affecting blood flow to the optic nerve and pre-existing microvascular damage in diabetic patients [3]. Dr. Joseph Rizzo at Harvard has received NIH funding to study GLP-1 receptors in optic nerve tissue [3].
Why it matters for patients
A Science Day does not change what any drug does or what any label says. It gives the judge a chance to hear experts before deciding how the cases should move forward [3]. The practical difference for patients is that Europe added a NAION warning while the United States has not, so the two regulatory systems currently say different things [3]. No bellwether trial has been set and no global settlement has been reported in MDL 3163 [1][3]. Whether GLP-1 drugs cause NAION, and in whom, has not been established by this proceeding; the studies above disagree on the size of the risk. Questions about individual symptoms are for a treating clinician, not for a court filing.
What happens next
Case-management and bellwether-selection steps are expected to follow the Science Day, which one source describes as a gating event [3]. Parvin Aminolroaya of Seeger Weiss leads the plaintiffs' executive committee [3]. Bellwether trials are likely years away given the MDL's December 2025 creation [3]. In the related MDL 3094, status conferences were set for June 23, July 14, October 13, November 17, and December 15, 2026, with a Rule 702 hearing window of September 10-18, 2026 for two cross-cutting issues [1].
Sources
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