- Semaglutide (Ozempic, Wegovy, Rybelsus) can very rarely cause NAION, a condition in which blood flow to the optic nerve drops: the EU drug regulator estimates about 1 extra case per 10,000 person-years of treatment.7
- The 2024 study that started the concern found NAION in 8.9% vs 1.8% of patients over 3 years, but it looked at people already referred to an eye specialist at one hospital.1 Nationwide studies found far lower rates, around 2 to 3 cases per 10,000 person-years.2
- The signal is clearest in people with type 2 diabetes. Studies of semaglutide for weight loss have not shown a clear increase.4,5
- Sudden vision loss or rapidly worsening eyesight in either eye needs urgent medical attention. Contact your doctor or go to an emergency department the same day.
What is NAION?
Nonarteritic anterior ischemic optic neuropathy (NAION) happens when blood flow to the front of the optic nerve drops. It is a serious cause of sudden, often permanent, vision loss.4 It is rare in anyone, and its main risk factors overlap with the conditions semaglutide is prescribed for.5 That overlap is why the question is hard to answer: people on semaglutide may have a higher risk to begin with.
The 2024 study that raised the alarm
Researchers at Massachusetts Eye and Ear, part of Harvard Medical School, searched the records of 16,827 patients seen by neuro-ophthalmologists at their hospital from 2017 to 2023.1 They compared people prescribed semaglutide with similar people on other diabetes or weight-loss medicines.
| Group | NAION over 36 months, semaglutide | Other medicines | Hazard ratio |
|---|---|---|---|
| Type 2 diabetes (710 patients) | 8.9% | 1.8% | 4.28 |
| Overweight or obesity (979 patients) | 6.7% | 0.8% | 7.64 |
These percentages are not the risk for a typical person on semaglutide. Everyone in the study had already been sent to an eye nerve specialist, so eye problems were far more common than in the general population. The numbers of events were small (17 vs 6 and 20 vs 3), and the authors themselves said the study could not prove cause.1
What larger studies found
Since then, much bigger studies have looked at whole populations. Their results point in different directions.
Denmark and Norway (2025). Using national health registries, researchers followed 61,377 adults with type 2 diabetes who started semaglutide and compared them with people who started an SGLT2 inhibitor, another diabetes medicine.2
The adjusted risk was about 2.8 times higher (hazard ratio 2.81), yet the authors stressed that the absolute risk "remains low".2 There were only 32 NAION cases in total.
A global health record network (2025). A study across 160 health care organizations in 21 countries matched about 297,000 people with type 2 diabetes, obesity or both. It found no significant link between semaglutide and NAION in any group over 1 to 3 years.3
Pooled analyses (2026). A meta-analysis of 8 randomized trials (31,174 patients) and 8 observational studies (over 1.6 million patients) split the results by why people took semaglutide:4
| Use and study type | Result |
|---|---|
| Diabetes, observational | 26.7 vs 18.9 cases per 100,000 person-years (about 2.7 vs 1.9 per 10,000); hazard ratio 1.85, significant |
| Diabetes, randomized trials | 5 events vs 1; no significant increase |
| Weight loss, observational | Hazard ratio 1.57; no significant increase |
| Weight loss, randomized trials | 4 events vs 1; no significant increase |
A second 2026 meta-analysis of six observational studies (about 4.8 million people) found no consistent overall increase, a raised risk in type 2 diabetes (adjusted hazard ratio 1.70) but not in obesity (0.47), and rated the evidence as low to very low certainty.5 A 2025 meta-analysis of 78 randomized trials did find higher odds of NAION with semaglutide (odds ratio 3.92), but with a very wide range of uncertainty, and said the data were not enough for firm conclusions.6
What regulators say
In June 2025 the European Medicines Agency's safety committee (PRAC) reviewed trials, post-marketing reports and the published studies. It concluded that NAION is a very rare side effect of semaglutide, meaning it may affect up to 1 in 10,000 people taking it.7 It noted that studies in adults with type 2 diabetes suggest roughly a doubling of risk, which works out to about one extra case per 10,000 person-years. It recommended adding NAION to the product information for Ozempic, Rybelsus and Wegovy.
In the US, the current Wegovy prescribing information on DailyMed (revised June 2026) does not list NAION.9 We could not find an FDA safety communication on it.
What about diabetic retinopathy?
This is a separate eye issue. In the SUSTAIN-6 trial of 3,297 adults with type 2 diabetes and high heart risk, retinopathy complications (such as bleeding in the eye or needing laser or injection treatment) were more common on semaglutide (hazard ratio 1.76).8 The US label gives the numbers: 3% vs 1.8% overall, 8.2% vs 5.2% in people who already had retinopathy, and 0.7% vs 0.4% in people who did not.9
The label notes that a rapid improvement in blood sugar has been linked to a temporary worsening of retinopathy, and that people with a history of retinopathy should be monitored.9 Across 78 randomized trials, semaglutide did not increase diabetic retinopathy overall (odds ratio 1.04).6 A long-term trial built to answer this question, FOCUS, is still running. More on GLP-1s in diabetes: GLP-1 weight loss in type 2 diabetes.
What this means in practice
- The absolute risk is small. Even the studies that found a link put it at roughly one or two extra cases per 10,000 people treated for a year.
- It is not settled. All of the large studies are observational, and they disagree. People with diabetes have more NAION risk factors to start with.
- Less is known about tirzepatide (Zepbound, Mounjaro). Most research so far is on semaglutide.
- Know the warning signs. The EMA advises anyone on semaglutide who has sudden vision loss or rapidly worsening eyesight to contact their doctor without delay, and says treatment should be stopped if NAION is confirmed.7
For other side effects, see GLP-1 nausea and stomach side effects and GLP-1 medicines and thyroid cancer.
Common questions
Can Ozempic cause blindness?
In June 2025 the European Medicines Agency's safety committee concluded that NAION, an optic nerve condition that can cause sudden and often permanent vision loss in one eye, is a very rare side effect of semaglutide (Ozempic, Wegovy, Rybelsus). It estimated about one extra case per 10,000 person-years of treatment, meaning one person taking it for one year.
How common is NAION on semaglutide?
In a Danish registry study of adults with type 2 diabetes, NAION occurred at 2.19 cases per 10,000 person-years in people starting semaglutide vs 1.18 in people starting an SGLT2 inhibitor. Across Denmark and Norway, the adjusted difference was about 1.4 extra cases per 10,000 person-years.
Is the NAION risk the same for weight loss and for diabetes?
Not clearly. A 2026 meta-analysis found a raised risk in observational studies of people with diabetes (hazard ratio 1.85), but no significant increase in observational studies of semaglutide for weight loss (hazard ratio 1.57) or in randomized trials for either use.
What did the Mass Eye and Ear study find about semaglutide and vision loss?
The 2024 Harvard study looked at patients seen by neuro-ophthalmologists at one Boston hospital. Over 36 months, NAION occurred in 8.9% of people with type 2 diabetes prescribed semaglutide vs 1.8% on other diabetes drugs, and in 6.7% vs 0.8% of people with overweight or obesity. Because these were referred eye patients, the percentages are far higher than in the general population.
Does semaglutide make diabetic retinopathy worse?
In the SUSTAIN-6 trial of 3,297 adults with type 2 diabetes, diabetic retinopathy complications occurred in 3% on semaglutide vs 1.8% on placebo, with a larger gap in people who already had retinopathy. A 2025 meta-analysis of 78 randomized trials found no overall increase in diabetic retinopathy (odds ratio 1.04).
Sources
- Hathaway JT, Shah MP, Hathaway DB, et al. Risk of Nonarteritic Anterior Ischemic Optic Neuropathy in Patients Prescribed Semaglutide. JAMA Ophthalmol. 2024;142(8):732-739. PubMed · Full text (PMC)
- Simonsen E, Lund LC, Ernst MT, et al. Use of semaglutide and risk of non-arteritic anterior ischemic optic neuropathy: A Danish-Norwegian cohort study. Diabetes Obes Metab. 2025;27(6):3094-3103. PubMed · Full text (PMC)
- Chou CC, Pan SY, Sheen YJ, et al. Association between Semaglutide and Nonarteritic Anterior Ischemic Optic Neuropathy: A Multinational Population-Based Study. Ophthalmology. 2025;132(4):381-388. PubMed
- Liu Z, Raveendran D, Fourlanos S, et al. Rate and Risk of Nonarteritic Anterior Ischemic Optic Neuropathy with Semaglutide Use for Diabetes and Weight Loss: A Systematic Review and Meta-Analysis. Ophthalmology. 2026;133(5):589-598. PubMed
- Abdelaal A, Abu Serhan H, Alsaadi M, et al. Semaglutide and the Risk of Nonarteritic Ischemic Optic Neuropathy: A Systematic Review and Certainty of Evidence Meta-Analysis. Ophthalmology. 2026;133(6):799-810. PubMed
- Natividade GR, Spiazzi BF, Baumgarten MW, et al. Ocular Adverse Events With Semaglutide: A Systematic Review and Meta-Analysis. JAMA Ophthalmol. 2025;143(9):759-768. PubMed · Full text (PMC)
- European Medicines Agency. PRAC concludes eye condition NAION is a very rare side effect of semaglutide medicines Ozempic, Rybelsus and Wegovy. 6 June 2025. EMA
- Marso SP, Bain SC, Consoli A, et al. Semaglutide and Cardiovascular Outcomes in Patients with Type 2 Diabetes. N Engl J Med. 2016;375(19):1834-1844. PubMed
- Novo Nordisk. WEGOVY (semaglutide) prescribing information. Revised 06/2026. DailyMed
