Ozempic, Mounjaro and Your Eyes: A Rare Risk Worth Knowing About

GLP-1 medicines such as Ozempic and Wegovy (semaglutide) and Mounjaro (tirzepatide) have changed how we treat diabetes and obesity. They lower blood sugar, help people lose meaningful weight, and semaglutide has also been shown to reduce major heart and blood vessel events and overall mortality. These are genuinely important medicines.

But there's one side effect that most people starting them haven't heard of, and it can cause permanent loss of vision in the affected eye.

What is NAION?

Medically called non-arteritic anterior ischemic optic neuropathy, or NAION (literally translating to damage to the front of the optic nerve from a poor blood supply), it's best thought of as a stroke of the optic nerve. The optic nerve is the cable that carries visual signals from the eye to the brain. When its blood supply suddenly drops, the nerve head swells and some of its fibres are lost. And those fibres don't grow back.

How strong is the link?

In June 2025, the European Medicines Agency's safety committee reviewed the available data, including clinical trials, post-marketing reports and the medical literature, and concluded that NAION is a very rare side effect of semaglutide, affecting up to 1 in 10,000 people taking it. In practical terms, large studies suggest semaglutide roughly doubles the risk, which works out to about one additional case for every 10,000 people treated for a year. The World Health Organization issued its own safety alert on this, while the US FDA listed NAION as a possible signal in 2025 and, as of September 2026, is still evaluating it, so US labels for Ozempic, Wegovy, Rybelsus and Mounjaro do not yet carry a warning, even as regulators in the UK and Australia have since acted on it too.

For Mounjaro, the evidence is less complete. A study of over 1.5 million people with type 2 diabetes found that semaglutide or tirzepatide was linked to a higher risk of NAION, though the overall risk stayed low. It's also worth knowing that much of the large-scale evidence comes from people with type 2 diabetes, so the risk for those using these drugs purely for weight loss is less clearly defined.

A 2026 update worth knowing: since that initial regulatory review, a considerable amount of new research has been published, and the picture has become, honestly, more nuanced rather than more settled. Some large studies have found a meaningfully increased risk, others, including a large propensity-matched analysis and a separate large retrospective cohort, have found no significant increase at all. In May 2026, the American Academy of Ophthalmology and the North American Neuro-Ophthalmology Society issued a joint consensus statement on exactly this question. Their conclusion: while many studies report a small possible increased risk of NAION with GLP-1 medicines, some studies report no correlation whatsoever, and the overall magnitude of the risk remains low.

So the risk, if it exists at the individual level, is real but small, and the evidence base, over a year on, is still actively evolving rather than fully resolved.

Who is at higher risk?

The optic nerve leaves the eye through a small opening at the back. In some people this opening is naturally narrow, so the nerve fibres and the tiny blood vessels that nourish them are packed tightly together. This is called a crowded optic disc, or a "disc at risk." Think of too many wires pushed through a small hole in a wall. There's no spare room, so even a little swelling can cut off blood flow and damage the nerve. People over 50 with a disc at risk appear to be the most vulnerable to GLP-1 related NAION. Diabetes, high blood pressure and sleep apnoea add to the risk as well.

So it's wise to have an eye examination before starting Ozempic or Mounjaro. The purpose of this exam is to look at your optic disc and see whether you fall into the higher-risk group. If you're diabetic, it's also a chance to check the retina, since semaglutide has been linked with worsening of diabetic retinopathy when sugar levels fall quickly.

That said, a normal-looking disc doesn't mean the risk is zero. NAION can still occur in eyes without a crowded disc.

What are the warning signs?

Typically, there's a sudden, painless drop in vision in one eye, often noticed on waking in the morning. Some people see a dark shadow over the upper or lower part of their vision. If this happens while you're on one of these medicines, see an eye specialist the same day. A proper examination and investigations are needed to rule out other serious conditions that can look similar.

Can it be treated?

Honestly, not reliably. There's currently no medical or surgical treatment proven to improve the outcome in acute NAION. Steroids have been tried, but randomised trials and a meta-analysis haven't shown a meaningful benefit, and they carry their own side effects, so routine use isn't recommended. That's why knowing about this risk before you start matters so much.

If NAION is confirmed, European regulators advise stopping semaglutide. This matters because the other eye can be affected in roughly 15% of people within five years. Any decision about stopping should be made together with the doctor managing your diabetes or weight.

Make informed choices

For most people, the benefits of these medicines far outweigh the risks, and my aim isn't to discourage anyone from using them. If you're planning to start Ozempic, Wegovy or Mounjaro, please discuss this with your endocrinologist or physician, and with your eye surgeon, so you can make a conscious, informed choice. And if you're already on one, report any sudden change in vision without delay.

Wishing you all the best.

Frequently Asked Questions

Can Ozempic cause vision loss?

Rarely, yes. European regulators have concluded that semaglutide (Ozempic, Wegovy) can cause NAION, a stroke of the optic nerve that may lead to permanent vision loss in the affected eye. It is classed as very rare, affecting up to 1 in 10,000 people.

Does Mounjaro carry the same eye risk?

The evidence for tirzepatide (Mounjaro) is less complete. A large study in people with type 2 diabetes found that semaglutide or tirzepatide was linked to a higher risk of NAION, though the overall risk remained low.

Do all studies agree that GLP-1 drugs increase NAION risk?

No, and this is worth understanding. A 2026 joint consensus statement from the American Academy of Ophthalmology and the North American Neuro-Ophthalmology Society noted that while many studies report a small possible increased risk, some studies find no correlation at all. The overall magnitude of risk remains low either way.

Should I get an eye test before starting Ozempic or Mounjaro?

It is wise to. An eye examination can identify a crowded optic disc, or disc at risk, which raises the chance of NAION. In diabetics it also checks the retina for diabetic retinopathy.

What are the symptoms of NAION?

A sudden, painless drop in vision in one eye, often noticed on waking. Some people see a dark shadow over the upper or lower part of their vision. See an eye specialist the same day.

Is NAION treatable?

There is currently no treatment proven to restore vision after NAION. Steroids have been tried but trials have not shown a meaningful benefit, and routine use is not recommended.

Should I stop Ozempic if I develop NAION?

European regulators advise stopping semaglutide if NAION is confirmed, as the other eye can be affected in about 15% of people within five years. Make this decision together with the doctor managing your diabetes or weight.

Does the US FDA warn about this on the label?

Not yet, as of September 2026. The FDA listed NAION as a possible safety signal in 2025 and has said it continues to evaluate the evidence, but current US prescribing information for Ozempic, Wegovy, Rybelsus and Mounjaro does not include an NAION warning, even though the EU, UK and Australia have acted.

Dr Mayank Bansal Vitreoretinal Surgeon, Claritas Eye & Retina Institute, New Delhi

References

• European Medicines Agency. PRAC concludes eye condition NAION is a very rare side effect of semaglutide medicines. June 2025.

• World Health Organization. Medical product alert: semaglutide medicines and risk of NAION. June 2025.

• Cai CX et al. Semaglutide or tirzepatide and optic nerve and visual pathway disorders in type 2 diabetes. JAMA Network Open, 2025.

• American Academy of Ophthalmology & North American Neuro-Ophthalmology Society. Glucagon-Like Peptide-1 Receptor Agonists and the Risk of Non-Arteritic Anterior Ischemic Optic Neuropathy: A Consensus Statement. 2026.

• American Academy of Ophthalmology. NAION: Diagnosis and Management. EyeNet.

• American Optometric Association. GLP-1 receptor agonists: clinical report.