Patients Sue GLP-1 Drugmakers Over Risk of Sudden Vision Loss: What the Evidence Shows

Updated September 25, 2026

Popular GLP-1-based medicines are now at the center of a growing legal and medical debate over a rare form of sudden vision loss called nonarteritic anterior ischemic optic neuropathy (NAION).

Patients in the United States have filed lawsuits against the manufacturers of widely used medicines including Ozempic, Wegovy, Mounjaro and Zepbound, alleging that the drugs caused NAION and that patients were not adequately warned about the potential risk.

Those lawsuits are allegations at the moment—not findings that the medications caused the injuries. The scientific evidence is still evolving and is not completely consistent.

Importantly, the regulatory evidence is stronger for semaglutide, the active ingredient in Ozempic, Wegovy and Rybelsus, than for the entire GLP-1 drug class.

Patient safety message: Sudden or rapidly worsening vision loss is not a symptom to monitor at home. Anyone experiencing sudden vision loss while taking a GLP-1-based medicine should seek urgent medical evaluation, because NAION and other causes of sudden vision loss require prompt assessment.

What is NAION?

Nonarteritic anterior ischemic optic neuropathy (NAION) is a disorder in which the optic nerve does not receive adequate blood flow, resulting in injury to the optic nerve head.

The typical presentation is sudden, painless vision loss, usually affecting one eye. Vision loss may be partial or substantial and can occur upon awakening. A swollen optic nerve is a characteristic finding during the acute phase.

NAION is different from retinal problems such as diabetic retinopathy. It is an optic-nerve condition, not simply a disease of the retina.

Established or suspected risk factors include diabetes, hypertension, high cholesterol, smoking, obstructive sleep apnea and an anatomically crowded optic disc with a small cup-to-disc ratio. These same risk factors are common among people being treated for obesity and type 2 diabetes, which makes it difficult to separate an effect of the medication from the underlying health conditions.

American Academy of Ophthalmology EyeWiki: NAION

Why are GLP-1 drugs being investigated?

The concern emerged after researchers began noticing reports of NAION among people receiving semaglutide and other incretin-based therapies.

A 2024 retrospective study from a neuro-ophthalmology referral population reported an association between semaglutide use and NAION. The study did not prove that semaglutide caused the condition, and its specialized referral setting limits how directly the findings can be generalized to all GLP-1 users.

PubMed: Risk of NAION in Patients Prescribed Semaglutide

European regulators concluded that NAION is a very rare semaglutide side effect

One of the most important developments occurred in 2025.

The European Medicines Agency's Pharmacovigilance Risk Assessment Committee reviewed clinical trials, post-marketing reports, observational studies and the medical literature. It concluded that NAION is a very rare adverse effect of semaglutide.

The EMA estimated the frequency at up to approximately 1 case per 10,000 people treated and reported that several large epidemiological studies suggested approximately a two-fold relative increase in NAION among adults with type 2 diabetes taking semaglutide.

The EMA recommended updating the product information for Ozempic, Wegovy and Rybelsus and advised that patients experiencing sudden loss of vision or rapidly worsening eyesight should contact a doctor without delay. When NAION is confirmed, the EMA recommends discontinuing semaglutide.

European Medicines Agency: Semaglutide and NAION

The FDA also identified NAION as a potential GLP-1 safety signal

The U.S. FDA's adverse-event monitoring program listed non-arteritic anterior ischemic optic neuropathy as a potential serious safety signal for the GLP-1 receptor agonist class in its October–December 2024 review.

The listing included semaglutide products as well as several other GLP-1 or incretin-based medicines, including tirzepatide products. The FDA stated that it was evaluating whether regulatory action was necessary.

That is an important distinction: an FDA potential safety signal is not the same thing as a confirmed causal relationship.

FDA: October–December 2024 Safety Signals

What do the latest studies show?

This is where the story becomes considerably more complicated.

Study 1: A 2026 meta-analysis found no statistically significant association

A systematic review and meta-analysis published in 2026 evaluated six observational studies involving approximately 4.83 million people.

The pooled analysis produced an odds ratio of 2.44, but the 95% confidence interval was very wide (0.59–10.15) and the authors rated the certainty of evidence as very low. The investigators therefore did not find a statistically significant association between semaglutide and NAION compared with non-GLP-1 therapies.

This illustrates why a relative-risk estimate alone should not be interpreted as proof of causation.

PubMed: Semaglutide and the Risk of NAION — Systematic Review and Meta-analysis

Study 2: Another 2026 meta-analysis found increased risk

A separate 2026 systematic review and meta-analysis reached a different conclusion. It reported that semaglutide was associated with an estimated 2.52-fold relative risk of NAION compared with non-GLP-1 treatment, with the authors describing the evidence as low-to-moderate certainty.

The study also emphasized the very low absolute frequency of the condition.

PubMed: GLP-1 Receptor Agonists and Risk of NAION

Study 3: A large pooled analysis of randomized trials did not show an excess of NAION

A separate pooled analysis of placebo-controlled trials involving approximately 96,829 participants identified three confirmed NAION cases among GLP-1-treated participants and five among placebo-treated participants.

The authors concluded that randomized trial data did not show an increased incidence of NAION with semaglutide or liraglutide compared with placebo.

This type of evidence is particularly important because randomized trials generally provide stronger protection against confounding than retrospective database studies, although rare adverse events can still be difficult to detect when the number of events is extremely small.

PubMed: NAION Incidence in Placebo-Controlled Liraglutide and Semaglutide Trials

Study 4: A large 2026 analysis found a modest class-level association

Another 2026 meta-analysis included 15 longitudinal studies and more than 1.5 million patients. It reported an odds ratio of 1.70 for NAION among GLP-1 receptor agonist users.

However, the estimated absolute risk difference was approximately 0.037%, corresponding to roughly 37 additional cases per 100,000 treated patients under the analysis assumptions.

That distinction between relative and absolute risk is critical. A statistically detectable increase in a very rare condition can still translate into a very small absolute increase in individual risk.

PubMed: Association Between GLP-1 Receptor Agonists and Ischemic Optic Neuropathy

What about Ozempic and Wegovy versus Mounjaro and Zepbound?

It is too early to treat all GLP-1-based medicines as identical for this issue.

Medicine Active ingredient Current evidence concerning NAION
Ozempic Semaglutide Most extensively studied signal; EMA classifies NAION as very rare.
Wegovy Semaglutide Same active ingredient; European regulatory warning applies.
Rybelsus Semaglutide Included in the EMA semaglutide safety review.
Mounjaro Tirzepatide Included in U.S. GLP-1 safety-signal monitoring, but direct evidence remains less developed.
Zepbound Tirzepatide Evidence for a specific NAION association remains uncertain.

Tirzepatide is a dual GIP/GLP-1 receptor agonist, so it should not automatically be assumed to carry exactly the same risk profile as semaglutide.

Real-world analyses published in 2026 have reported differences between individual incretin medicines, but these findings are observational and require further validation before they can be used to establish comparative safety.

How many lawsuits have been filed?

The litigation is no longer limited to isolated individual complaints.

The U.S. Judicial Panel on Multidistrict Litigation established MDL No. 3163, formally titled In re: Glucagon-like Peptide-1 Receptor Agonists (GLP-1 RAs) Non-Arteritic Anterior Ischemic Optic Neuropathy Products Liability Litigation.

According to the Judicial Panel's September 1, 2026 report, 216 actions were pending in MDL 3163.

The existence of an MDL does not mean the plaintiffs have established that GLP-1 medicines caused NAION. Multidistrict litigation is a procedural mechanism used to coordinate cases involving common factual questions.

U.S. Judicial Panel on Multidistrict Litigation: September 1, 2026 Report

The original transfer order states that plaintiffs allege that certain GLP-1 drugs caused NAION and assert claims involving issues such as warning adequacy, design and product liability. Those allegations remain matters for litigation and evidence.

JPML: MDL 3163 Transfer Order

Why proving causation is difficult

The central scientific question is not simply:

"Did someone develop NAION while taking a GLP-1 drug?"

Instead, researchers must determine whether the medication causes more NAION than would otherwise be expected in comparable people who are not exposed to the drug.

That is difficult because obesity, diabetes, hypertension, dyslipidemia and sleep apnea are themselves associated with NAION. These conditions are also common reasons people receive GLP-1-based therapy.

This creates potential confounding by indication.

Another issue is the rarity of NAION. When an outcome occurs only a few times per 100,000 people, very large datasets are required to distinguish a true drug effect from statistical noise or differences between patient populations.

Could rapid metabolic change also matter?

Researchers have raised another important hypothesis: the relationship may not be explained entirely by a direct effect of the drug on the optic nerve.

GLP-1 medicines can produce substantial changes in body weight, blood glucose, blood pressure, hydration and metabolic status. Rapid improvement in blood glucose can also affect diabetic retinopathy independently of NAION.

A 2026 observational study reported that NAION risk among GLP-1 receptor agonist initiators was higher during the first six months and was associated with factors including a greater reduction in HbA1c.

These findings are hypothesis-generating rather than proof of mechanism, but they reinforce the importance of considering the entire clinical context rather than attributing every case solely to the medication.

PubMed: GLP-1 RAs and NAION in Type 2 Diabetes

Who may already be at higher baseline risk?

NAION has recognized associations with several vascular and anatomical factors.

Potential risk factor Why it matters
Diabetes Associated with vascular disease and higher baseline NAION risk.
Hypertension A recognized vascular risk factor.
High cholesterol Associated with vascular risk.
Smoking Contributes to vascular risk.
Obstructive sleep apnea Has been associated with NAION in observational studies.
Small or crowded optic disc An important anatomical susceptibility factor.
Previous NAION in the other eye Increases concern for involvement of the fellow eye.

Emergency symptoms: when to seek help

Sudden vision loss should be treated as an urgent medical problem regardless of whether you take a GLP-1 medicine.

Warning signs include:

  • Sudden loss of vision in one eye
  • A new dark or blurred area in the visual field
  • Rapidly worsening eyesight
  • A sudden "missing" area of vision
  • New distortion or major change in vision

NAION is only one possible explanation. Retinal vascular occlusion, retinal detachment, stroke, optic neuritis, giant-cell arteritis and other conditions can also cause sudden visual symptoms.

Do not assume that sudden vision loss is simply a medication side effect.

Should patients stop their GLP-1 medicine?

Do not make a medication decision based solely on a lawsuit or news report.

The appropriate response depends on why the drug was prescribed, the specific medicine, the dose, the patient's cardiovascular and metabolic risk, and the nature of the visual symptoms.

For patients taking semaglutide who experience sudden vision loss, the EMA recommends urgent medical evaluation. When NAION is confirmed, the EMA recommends stopping semaglutide.

That is different from advising every person taking a GLP-1 medicine to discontinue treatment pre-emptively.

The bigger picture: rare eye risk versus proven benefits

GLP-1-based therapies have demonstrated clinically important benefits for appropriate patients with obesity and/or type 2 diabetes, including improvements in glycemic control, weight management and, for some approved products and populations, cardiovascular or kidney outcomes.

At the same time, a potentially serious adverse event deserves attention even when it is rare.

The correct scientific question is therefore not whether GLP-1 medicines are simply "safe" or "dangerous." The more useful question is:

For a particular patient, what are the expected benefits, the established risks, the uncertain risks and the available alternatives?

What patients should discuss with their clinician

Before starting or continuing a GLP-1-based medicine, a patient concerned about NAION can ask:

  • What is my baseline risk for NAION?
  • Do I have diabetes, hypertension, sleep apnea or other vascular risk factors?
  • Have I ever experienced NAION or another optic-nerve disorder?
  • Do I have symptoms that warrant an eye examination before treatment?
  • Which GLP-1 or incretin-based medication is being considered, and what is known about its specific safety profile?
  • How quickly are my glucose, blood pressure and weight expected to change?
  • What symptoms should trigger immediate medical attention?

Bottom line

GLP-1 drugs and sudden vision loss are now a legitimate subject of pharmacovigilance, clinical research and litigation. The concern centers primarily on NAION, a rare optic-nerve disorder that can cause sudden and sometimes permanent visual impairment.

The evidence in 2026 remains mixed. European regulators have concluded that NAION is a very rare adverse effect of semaglutide, while multiple 2026 systematic reviews have produced different estimates of risk. Randomized-trial data have not demonstrated a clear increase, and the evidence for a class-wide effect across all GLP-1-based medicines remains uncertain.

The lawsuits therefore should not be presented as proof that GLP-1 drugs cause blindness. They are part of an ongoing legal process occurring alongside an evolving scientific safety question.

For patients, the most important practical point is simple: new sudden vision loss requires urgent medical evaluation. The decision to start, continue or stop a GLP-1 medicine should be individualized with the prescribing clinician, with particular attention to the patient's indication, baseline risk factors and the emerging evidence about rare ocular complications.

Editor's note: OneDayMD tracks emerging safety signals while distinguishing between adverse-event reports, observational associations, randomized clinical-trial evidence, regulatory conclusions and legal allegations. Evidence can change as new studies and regulatory reviews become available.

Medical disclaimer: This article is for educational purposes only and is not a substitute for diagnosis or individualized medical advice. Sudden vision loss is a medical emergency and should be evaluated promptly by an appropriate healthcare professional.

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