Ozempic, Mounjaro face lawsuits in the US over vision loss. What's the risk?

US lawsuits have put a spotlight on claims that GLP-1 based drugs may be linked to the rare eye condition NAION. Doctors say the evidence remains mixed, with no reported cases in India so far and the risk still under investigation.

In Short

• Patients claim they developed sudden, painless vision loss months after treatment began
• Novo Nordisk and Eli Lilly dispute claims as regulators review data
• European regulators list NAION as a very rare semaglutide side effect

A wave of lawsuits in the US alleging vision loss linked to popular weight-loss and diabetes drugs has brought a rare eye condition into focus, raising questions about the long-term safety of medicines that have rapidly gained popularity worldwide.

The litigation centres on non-arteritic anterior ischaemic optic neuropathy (NAION), a condition that can cause sudden, potentially irreversible vision loss.

Plaintiffs have alleged that drugs belonging to the GLP-1 class, including semaglutide-based Ozempic and Wegovy, were responsible for their injuries and that manufacturers failed to adequately warn patients about the risk.

But the allegations do not establish that the drugs caused the condition. The possible association between GLP-1 medicines and NAION remains under scientific investigation, with researchers examining whether the risk is real, how large it might be, and which patients could be vulnerable.

In India, where injectable GLP-1 based therapies are now available for diabetes and weight management, the debate has a particular relevance. There have been no reported cases of NAION linked to these drugs in India so far, say senior doctors, adding that the possible association warrants attention but should be distinguished from established drug-related harm.

GLP-1, or glucagon-like peptide-1, is a gut hormone that helps regulate blood sugar and appetite. GLP-1 receptor agonists mimic this hormone, stimulating insulin release when blood sugar is high, slowing stomach emptying and making people feel full for longer.

The drugs – initially developed to treat type 2 diabetes – due to their ability to reduce appetite and body weight, have emerged as a major treatment option for obesity.

Semaglutide is sold as Ozempic for type 2 diabetes and, at a different dose, as Wegovy for weight management. Tirzepatide, sold as Mounjaro and Zepbound in different markets and indications, acts on both GLP-1 and GIP receptors.

Their effectiveness has fuelled extraordinary demand, with millions of people using them. But as prescriptions have expanded, rare adverse events that may not emerge in trials involving a few thousand participants are receiving greater scrutiny.

RARE BUT SERIOUS CONCERN

NAION is a rare condition in which reduced blood supply to the optic nerve causes sudden, usually painless vision loss. Often described as an “eye stroke”, it can cause permanent damage, typically affecting one eye.

It is different from diabetic retinopathy, a condition in which high blood sugar damages the blood vessels in the retina. And though both are now being discussed in relation to GLP-1-based medicines, but involve different parts of the eye and different mechanisms of injury.

The lawsuits allege that patients developed NAION after taking GLP-1 drugs and that manufacturers did not adequately warn them about the potential risk. Some patients have reported symptoms within months of starting treatment.

Reports suggest that over 90 lawsuits have been filed against Novo Nordisk in New Jersey since 2025, with additional cases brought in federal court in Pennsylvania. The litigation targets manufacturers including Novo Nordisk, which makes Ozempic and Wegovy, and Eli Lilly, maker of Mounjaro and Zepbound.

The companies dispute the allegations. Novo Nordisk has said its own research has found no increased risk of NAION, while Eli Lilly has said it is reviewing the available data. The US Food and Drug Administration is investigating the possible link, but has not added a specific NAION warning to GLP-1 drug labels.

SCIENTIFIC EVIDENCE SO FAR

The scientific evidence remains mixed. Some observational studies have reported a possible association between semaglutide and NAION, while other research, including a Novo Nordisk-funded study, has not found an increased risk.

The European Medicines Agency has classified NAION as a very rare side effect of semaglutide, estimating that it could affect up to one in 10,000 people taking the drug for diabetes. The American Academy of Ophthalmology and the North American Neuro-Ophthalmology Society have also noted that, while a small increase in risk is possible, the overall magnitude of the risk remains low.

Dr V Mohan, a Chennai-based diabetologist and researcher told India Today that the possible association should be seen in the context of how rare the condition is and the difficulty of detecting such events in clinical trials.

“Clinical trials are normally done in a few thousand people,” he said, explaining that rare adverse events may only become apparent when medicines are used by millions of people.

Dr Mohan said isolated reports of NAION have emerged among GLP-1 users, but whether the drugs directly cause the condition remains unresolved.

The US FDA, since mid-2024 after the first such case was reported, has been investigating the concerns but so far has not mandated any black box warning, the strongest safety related alert on these drugs so far, while such a warning is applicable to warn users about the extremely rare risk of thyroid cancer upon using these medicines.

Dr Mohan's institute, Madras Diabetes Research Foundation (MDRF) is also part of the international FOCUS study, which is examining the effect of semaglutide on diabetic retinopathy.

Results are expected to help clarify the separate question of whether the drug affects the progression of retinal disease, which also is a common complication of diabetes itself.

Dr Mohan, however, cautioned against conflating the two eye conditions. While he advises against GLP-1 use in patients with very severe retinopathy until more evidence is available, he said NAION is a distinct, rare condition that can also occur in people who have never taken these medicines.

The clinician-scientist said large health databases are needed to establish whether the apparent association is genuine, given that individual clinicians are unlikely to encounter enough cases to draw firm conclusions.

“The last word has not been told on that,” he said, adding that the potential risk needs to be investigated without losing sight of the medicines' benefits for patients who need them.

INDIA'S SAFETY QUESTION

In India, the possible risk is worth tracking as GLP-1 medicines become more widely available for diabetes and obesity.

Injectable semaglutide and tirzepatide are already being used in a big way in the country since last year, but multiple doctors said there have been no reported cases of NAION linked to these drugs in India so far.

In part, it could also be attributed to the comparatively shorter period and smaller scale of use in India than in the US, where the medicines were adopted earlier.

The absence of reported cases, however, does not establish that the risk is absent, many feel.

"India is not a country with very strong pharmacovigilnace and that's a challenge," said a public health activist.

The NAION litigation is not the first legal challenge to GLP-1 manufacturers over serious adverse events.

In March this year, the family of a 76-year-old US woman filed a wrongful-death lawsuit against Novo Nordisk, alleging that she developed severe stomach paralysis after nearly six months on Ozempic and subsequently died.

It was reported as the first known death-related lawsuit involving the drug. The case came days after the FDA issued Novo Nordisk a warning over deficiencies in reporting suspected serious adverse events, including deaths. The regulator did not establish that the drug caused the reported outcomes.

Other lawsuits have alleged that GLP-1 drugs caused gastroparesis, or severe slowing of stomach emptying, alongside persistent nausea, vomiting and other gastrointestinal complications. Reports of other serious adverse events, including gallbladder problems and vision loss, have also prompted closer scrutiny. Such reports and lawsuits, however, do not by themselves establish causation.

- Ends