A rare form of sudden and potentially permanent vision loss is becoming the latest safety question surrounding blockbuster GLP-1 drugs, with patients filing lawsuits in the U.S. even as regulators overseas have already added warnings.
The condition is called nonarteritic anterior ischemic optic neuropathy, or NAION. It occurs when blood flow to the optic nerve is reduced, potentially causing abrupt vision loss that can be permanent.
The complication appears to be extremely rare. The bigger issue is that researchers still disagree over whether drugs such as Ozempic and Wegovy actually cause it.
That uncertainty is now moving from medical journals into courtrooms and regulatory agencies.
Patients Are Taking Novo Nordisk and Eli Lilly to Court
More than 90 lawsuits have been filed in New Jersey state court since 2025 on behalf of patients who developed NAION while taking Novo Nordisk’s Ozempic or Wegovy, according to the source material reviewed by Global Market News.
Additional federal lawsuits target Novo Nordisk and Eli Lilly, which makes Mounjaro and Zepbound.
The plaintiffs argue that the drugs caused their vision loss and that manufacturers failed to adequately warn patients about the potential risk.
Both companies dispute those claims.
Novo Nordisk says the lawsuits are without merit and maintains that available evidence does not establish that its drugs cause NAION. Eli Lilly has similarly argued that existing research does not prove GLP-1 medications cause the condition.
That distinction matters.
Researchers have found an association between semaglutide and NAION in several studies. An association does not establish that semaglutide itself caused the vision loss.
Still, the signal has become difficult for regulators to ignore.
Europe Has Already Taken Action
The European Medicines Agency reviewed clinical trials, post-marketing surveillance, scientific literature and other available evidence before concluding in 2025 that NAION should be classified as a very rare side effect of semaglutide.
European regulators estimated that it could affect up to roughly 1 in 10,000 people taking semaglutide.
Several large epidemiological studies reviewed by European regulators suggested semaglutide exposure among adults with Type 2 diabetes was associated with approximately twice the risk of developing NAION.
Warnings or information about NAION have also appeared on drug labeling in countries including the U.K., Japan and Australia.
The United States has taken a more cautious approach.
The FDA has been evaluating the potential connection, but U.S. labeling has not carried the same NAION warning described overseas.
That regulatory difference could become increasingly important if more evidence emerges.
The Numbers Sound Scary Until You Look at the Absolute Risk
This is where the GLP-1 vision story requires some perspective.
A doubling of risk sounds enormous. With an extremely rare condition, however, doubling a tiny number still produces a tiny number.
One large U.S. study of veterans with Type 2 diabetes found semaglutide users had more than twice the risk of developing NAION compared with patients beginning another class of diabetes medications.
Yet the absolute numbers remained low.
The estimated cumulative risk was approximately 0.29% among semaglutide users versus 0.13% among patients taking SGLT2 inhibitors over a median follow-up period of about 2.1 years.
Another large multicenter analysis found a much smaller increase in relative incidence and concluded that additional research was necessary to determine causality.
A systematic review of randomized trials also detected a possible increased occurrence of NAION, but researchers cautioned that the number of cases was extremely small and the evidence remained imprecise.
So there are really two findings investors and patients need to hold at the same time:
There is enough evidence for regulators and doctors to pay attention.
There is still considerable uncertainty about how large the risk actually is and whether the drugs directly cause it.
Why This Matters for Novo Nordisk and Eli Lilly
For investors, the immediate financial threat is unlikely to come from large numbers of patients suddenly developing NAION. The condition remains rare.
The bigger risk is what happens to the warning label.
Ozempic, Wegovy, Mounjaro and Zepbound sit at the center of one of the pharmaceutical industry’s most valuable growth markets. Millions of patients use GLP-1 drugs for diabetes and obesity, and drugmakers are pursuing additional indications that could expand the market further.
When a medicine reaches that scale, even an extremely rare side effect can become financially meaningful.
A stronger U.S. warning could affect physician conversations, patient perceptions and litigation. It could also create an opening for competitors if one drug or molecule eventually develops a cleaner perceived safety profile.
That does not mean GLP-1 demand suddenly collapses.
These drugs have demonstrated substantial benefits for weight loss, blood sugar control and, for certain patients, cardiovascular and kidney outcomes. Doctors therefore have to weigh a very small potential vision risk against benefits that can be significant.
That risk-benefit calculation could look very different for someone with serious obesity and Type 2 diabetes than for someone primarily interested in losing a small amount of weight.
The Real Risk for Drugmakers May Be Disclosure
The lawsuits could eventually hinge on something slightly different from the scientific question of whether GLP-1 drugs definitively cause NAION.
Plaintiffs are also arguing they should have been warned about the potential association.
That makes the overseas labels particularly relevant.
If European and other regulators believe the evidence warrants informing patients about NAION, attorneys in the U.S. can point to those decisions when arguing that American patients should have received similar information.
Drugmakers can counter that different regulators use different standards and that scientific evidence remains mixed.
That battle could become more consequential than the raw incidence numbers.
For Novo Nordisk and Eli Lilly investors, there are therefore three separate risks to follow: medical risk, regulatory risk and legal risk.
They do not necessarily move together.
The medical risk can remain extremely small while regulatory and litigation exposure grows.
What Patients Should Know
NAION usually causes sudden, painless vision loss, often affecting one eye. There is currently no approved treatment capable of restoring the vision that has been lost.
People with diabetes, high blood pressure, cardiovascular disease and sleep apnea may already have elevated risk factors independent of GLP-1 treatment, which is one reason researchers have had difficulty determining how much additional risk might come from the medication itself.
Patients should not stop a prescribed GLP-1 medication based solely on reports of a potential association. Anyone taking these drugs who is concerned about eye health should discuss their individual risk factors with their physician or eye-care provider.
Sudden changes in vision warrant prompt medical evaluation.
The Next Decision Could Come From the FDA
The most important development now is what U.S. regulators decide to do.
If the FDA eventually requires NAION information to be added to semaglutide labeling, it would bring the U.S. closer to the position already taken by European regulators and could strengthen plaintiffs’ arguments that the risk deserves greater disclosure.
If regulators decide the evidence remains insufficient for a warning, that would support the drugmakers’ position that a causal connection has yet to be established.
Either way, this is becoming another test of what happens when medicines used by millions of people encounter a potentially serious side effect that may affect only a tiny fraction of them.
For investors, the number to watch may ultimately be less important than the label.
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