A large US study has linked GLP-1 drugs, including semaglutide (Ozempic, Wegovy) and tirzepatide (Mounjaro, Zepbound), to a small increase in the risk of ischemic optic neuropathy, a condition that can cause sudden, often permanent vision loss in one eye. The study, led by researchers at Rutgers University and published in the Annals of Internal Medicine, found the extra risk to be about 3 to 4 cases per 10,000 people treated over 18 months.

What the study found

The researchers analyzed a large US health database of adults aged 18 to 65 with type 2 diabetes who had recently started either a GLP-1 drug or another diabetes medication. Those starting GLP-1 drugs had a modestly higher rate of ischemic optic neuropathy. Cases were more common in men and in the older group, aged 50 to 65. About one-third of affected patients recovered some vision, usually within six months, but most were left with some lasting impairment.

What ischemic optic neuropathy is

The optic nerve carries visual signals from the eye to the brain. In ischemic optic neuropathy, its blood supply is suddenly reduced, damaging the nerve — in effect, a small stroke of the optic nerve. More than 80% of cases are the non-arteritic anterior form, known as NAION. It typically causes painless vision loss in one eye, often noticed on waking, sometimes as a dimming, blurring, or a missing upper or lower half of the visual field. There is no proven treatment to restore lost vision.

How this fits with earlier evidence

Concern about GLP-1 drugs and NAION first surfaced in 2024, when a study from a Boston eye hospital reported a higher rate among patients prescribed semaglutide. Results since then have been mixed: some studies found an association, others did not, and several suggested any risk is small. In 2025, European regulators concluded that NAION is a very rare side effect of semaglutide and updated product information accordingly. The new study adds a large, US-based estimate of the absolute risk, and extends the question to tirzepatide.

Putting the risk in perspective

Three to four extra cases per 10,000 people over a year and a half means that for every 10,000 people with diabetes who start a GLP-1 drug, roughly 9,996 will not develop this complication because of it. Against that, GLP-1 drugs lower blood sugar, help people lose weight, and in people with heart disease reduce heart attacks and strokes. Uncontrolled diabetes is itself a leading cause of vision loss. For most patients, the benefits are likely to outweigh this small risk. But that calculation is individual, and NAION is serious when it happens, which is why the authors say patients and clinicians should be aware of it.

Why a link might exist

The mechanism is not known. One idea is that rapid improvements in blood sugar, or shifts in blood pressure and fluid balance during treatment, could briefly reduce blood flow to the optic nerve in people who are already vulnerable — for example, those with a small, crowded optic disc, sleep apnea, or vascular disease. Many of the same risk factors, including diabetes, high blood pressure and obesity itself, also raise the risk of NAION independently of any drug. That overlap is exactly what makes the question hard to settle with observational data, and why researchers want studies that compare people with very similar health profiles.

The limitations

This is an observational study. People who start GLP-1 drugs may differ from those who start other diabetes medicines in ways that affect their risk, and the authors stress that the results do not prove that GLP-1 drugs damage the optic nerve. NAION can also be misclassified in insurance-type data. The study included only people with type 2 diabetes up to age 65, so it does not directly answer the question for people using these drugs for weight loss alone, or for older adults.

What patients should do

Do not stop a prescribed GLP-1 drug because of this study without talking to your doctor. Do know the warning signs. Sudden blurring, dimming or loss of part of the vision in one eye needs same-day evaluation by an eye doctor or emergency department. People with existing optic nerve problems, a previous NAION, or other eye conditions may want to discuss the risk before starting treatment. Lead author Chintan Dave said early recognition of symptoms and prompt eye evaluation may be especially important for higher-risk patients.

What comes next

Researchers still need to establish whether the drugs cause NAION, which patients are most at risk, and whether risk varies between drugs, doses or the speed of dose increases. Answers will matter more as GLP-1 use expands to tens of millions of people, including many without diabetes. For a broader look at the drugs’ side effects, see our guide to GLP-1 side effects. This is research news, not medical advice.