Semaglutide and sudden vision loss
Semaglutide, the drug in Ozempic and Wegovy, has been linked to a rare stroke of the optic nerve that takes sight in one eye suddenly, painlessly and largely for good. The first, alarming figure came from a specialist referral clinic; across a whole national population the extra risk was about one case per 10,000 years of treatment, and later studies disagree on whether the risk is raised at all.
If you take semaglutide, treat any new, painless loss of vision in one eye as urgent and get same-day eye care; if the diagnosis is confirmed, the drug should be stopped. The risk is very small in absolute terms, but it belongs in the decision to start.
What it is
The condition is non-arteritic anterior ischaemic optic neuropathy (NAION): the front of the optic nerve, the cable that carries vision from the eye to the brain, loses its blood supply. It causes a painless loss of vision in one eye, and most of that loss is permanent. It is now a listed side effect of semaglutide in Europe and the UK.
The first alarm overstated the risk
A 2024 matched study at a single specialist referral centre for eye-nerve disease raised the alarm: among people with type 2 diabetes, 8.9% of those on semaglutide developed NAION over three years, against 1.8% of those on other, non-GLP-1 diabetes drugs.[1] Those figures describe people already sent to a specialist, not ordinary users, so they cannot be read as the risk for someone starting the drug.
What whole-population studies show
The population-scale numbers are far smaller, and all of them come from observational data:
- Denmark. Across all 424,152 Danes with type 2 diabetes, semaglutide roughly doubled the risk, but from a very low base: about 0.23 against 0.09 cases per 1,000 person-years, or about one extra case per 10,000 years of treatment. The median time from first prescription to the event was 22 months.[2]
- A large matched study. In 174,584 matched pairs with diabetes, risk was roughly 2.4 times higher at two and three years, with no detectable excess in the first year.[3]
- Fourteen US health-record databases. In about 810,000 new semaglutide users with type 2 diabetes, risk against other diabetes drugs was 23–44% higher, but not statistically significant under the broad definition of the condition. Only the comparison with one drug, empagliflozin, under the strict definition reached significance, at about 2.3 times the risk. Comparing the same people on and off the drug gave a modest 32% increase.[4]
Why the size of the risk is disputed
Two 2026 meta-analyses of the observational studies came out differently. One pooled six studies and found no significant increase overall, at low certainty; split by group, the risk was raised in type 2 diabetes (about 1.7 times) but not in obesity.[5] The other, using a different statistical approach, put the risk at about 2.5 times.[6]
The randomised trials point the other way. Pooling the manufacturer's placebo-controlled trials of liraglutide and semaglutide, in 96,829 participants, found no excess: about 3 confirmed cases per 100,000 person-years on the drugs against about 6 on placebo. Three of its authors work for the manufacturer, and its result sits awkwardly with a regulator's statement that the trials show a slightly higher risk than placebo.[7]
Most of the data come from people with type 2 diabetes. For people taking the drug for weight alone, the evidence is thinner, and the one meta-analysis that looked separately found no signal there, though the early referral-clinic study saw one in people with obesity too.
What regulators say
European regulators concluded in June 2025 that NAION is a very rare side effect of semaglutide, affecting up to 1 in 10,000 people, and added it to the product information. The UK followed in February 2026.[8] The US label still carries no NAION language. Regulators are explicit that treatment should be stopped if NAION is confirmed.
What to do
- Know the symptom. Sudden, painless dimming or loss of vision in one eye while on semaglutide needs same-day eye care, not a wait to see if it clears. Other causes of sudden vision loss are emergencies too; see Vision.
- If NAION is confirmed, stop the drug with your prescriber.
- Weigh it, don't fear it. At about one extra case per 10,000 years of treatment in the largest national study, this is not on its own a reason to refuse a drug that cuts heart attacks and strokes in people who need it. The wider trade-offs are on Ozempic-class drugs.
Further reading
- Hathaway JT et al. Risk of Nonarteritic Anterior Ischemic Optic Neuropathy in Patients Prescribed Semaglutide. JAMA Ophthalmol 2024.[9]
- Grauslund J et al. Once-weekly semaglutide doubles the five-year risk of nonarteritic anterior ischemic optic neuropathy in a Danish cohort of 424,152 persons with type 2 diabetes. Int J Retina Vitreous 2024.[10]
- Hsu AY et al. Semaglutide and Nonarteritic Anterior Ischemic Optic Neuropathy Risk Among Patients With Diabetes. JAMA Ophthalmol 2025.[11]
- Cai CX et al. Semaglutide and Nonarteritic Anterior Ischemic Optic Neuropathy. JAMA Ophthalmol 2025.[12]
- Abdelaal A et al. Semaglutide and the Risk of Nonarteritic Ischemic Optic Neuropathy: A Systematic Review and Certainty of Evidence Meta-Analysis. Ophthalmology 2026.[13]
- Vilsbøll T et al. Non-arteritic anterior ischaemic optic neuropathy incidence in placebo-controlled clinical trials of liraglutide or semaglutide. Br J Ophthalmol 2026.[14]