Ozempic and Vision Loss: What the NAION Research Actually Means for You

What NAION Is — and Why It Matters

NAION stands for non-arteritic anterior ischemic optic neuropathy. It is a condition where blood flow to the optic nerve is suddenly reduced — essentially a stroke of the optic nerve. The optic nerve carries all visual information from the eye to the brain. When its blood supply is interrupted, the nerve fibres begin to die within minutes to hours, and the vision loss that results is typically permanent.

NAION is the most common cause of sudden severe optic nerve injury in people over 50. Even before any association with GLP-1 medications, it affected approximately 2–10 people per 100,000 per year in the general population. It usually affects one eye at a time. Approximately 15% of people who experience NAION in one eye go on to develop it in the other eye within five years.

The hallmark of NAION is that it is painless. Unlike a headache or a sudden eye injury, NAION does not hurt. Many people notice it when they wake up in the morning with vision already significantly reduced in one eye. This painless onset is one of the reasons people sometimes delay seeking care — they hope it will resolve on its own. It does not. Time matters significantly with this condition.

The Research Timeline: How the Evidence Developed

The story of how NAION became associated with semaglutide is worth understanding because it explains why this finding emerged recently rather than at the time of approval.

The Mass Eye and Ear case series (2023–2024)

Dr Joseph Rizzo, a neuro-ophthalmologist at Mass Eye and Ear in Boston, first noticed an unusual pattern in his practice. Over a short period he saw three patients with NAION who had all been taking semaglutide. He teamed up with colleagues to analyse the records of 17,000 patients treated since semaglutide first received FDA approval.

The analysis separated cases into two groups — patients with diabetes and patients with obesity — and compared those taking semaglutide against those taking other medications. The findings were striking. People with diabetes taking semaglutide were 4.28 times more likely to develop NAION than comparable patients on other diabetes medications. Those using semaglutide for obesity were 7.64 times more likely to develop NAION than similar patients not on the drug.

This analysis was published in JAMA Ophthalmology in July 2024. Dr Rizzo was careful about the implications: he explicitly stated he would not use these findings to recommend patients stop their medications. But he described it as the first possible significant negative finding with these drugs and argued it merited extra caution in prescribing decisions.

The EMA formal review (2025)

The European Medicines Agency’s Pharmacovigilance Risk Assessment Committee began a formal review of semaglutide and NAION following the Mass Eye and Ear publication and additional reports. In June 2025, following a comprehensive review of clinical trial data, post-marketing surveillance, and epidemiological studies, the PRAC concluded that NAION is a very rare side effect of semaglutide, affecting up to 1 in 10,000 people treated.

The EMA recommended that the product information for all semaglutide medicines — Ozempic, Rybelsus, and Wegovy — be updated to include NAION as a very rare side effect. The committee simultaneously maintained that the medications’ benefits outweigh their risks for approved indications.

The large JAMA study (February 2025)

A follow-up study published in JAMA in February 2025 analysed health records for more than 37 million adults with type 2 diabetes, of whom more than 810,000 had been prescribed semaglutide. The incidence rate of NAION among semaglutide users was just over 14 cases per 100,000 person-years — approximately 1.8 times the rate in those prescribed other diabetes medications. This larger study found a smaller relative risk than the original Mass Eye and Ear analysis, which may reflect differences in study population and methodology.

Federal litigation (December 2025)

In December 2025, the Judicial Panel on Multidistrict Litigation centralised lawsuits alleging vision loss from GLP-1 drugs under MDL-3163 in Pennsylvania federal court under Judge Karen Spencer Marston. The lawsuits allege that Novo Nordisk failed to adequately warn consumers about the NAION risk associated with semaglutide. This litigation is ongoing as of March 2026.

Who Is Most at Risk

NAION does not occur randomly. It has well-established risk factors that exist independently of GLP-1 medications. Understanding these factors is important because people with multiple risk factors face a compounded risk when taking semaglutide.

• Small or crowded optic disc. This is an anatomical feature of the eye — some people have a smaller optic nerve head with less space for blood vessels. This structural characteristic predisposes to NAION regardless of any medication. People with this anatomy are described as having a disc at risk. An ophthalmologist can identify this during a routine eye examination.
• Pre-existing vascular disease. High blood pressure, diabetes, high cholesterol, and atherosclerosis all damage small blood vessels throughout the body, including those supplying the optic nerve. People with type 2 diabetes already have higher baseline NAION risk — which is part of why the relative risk figure for the diabetes group in the JAMA study is clinically important despite being lower than the obesity group figure.
• Sleep apnoea. Obstructive sleep apnoea causes repeated episodes of low blood oxygen during sleep. The optic nerve is particularly vulnerable to oxygen deprivation, and sleep apnoea is an established independent risk factor for NAION. It is also highly prevalent among people with obesity — the same population most commonly prescribed semaglutide for weight management.
• Age over 50. NAION is predominantly a condition of middle age and older adults. The American Academy of Ophthalmology notes it is the most common cause of sudden severe optic nerve injury in people over 50.
• Previous NAION in one eye. Approximately 15% of people who experience NAION in one eye develop it in the other eye within five years. If you have had NAION previously, your risk of a second episode is elevated regardless of medication.
• Using semaglutide for obesity rather than diabetes. The JAMA 2024 data found the relative risk was substantially higher in the obesity group than in the diabetes group. This may relate to the higher doses used in weight management — Wegovy is dosed up to 2.4mg weekly compared to Ozempic’s maximum of 2mg for diabetes.

Why Semaglutide May Cause NAION

The mechanism is not fully established, and researchers have been honest about this uncertainty. Several hypotheses have been proposed based on what is known about how semaglutide affects the body.

One leading hypothesis relates to changes in blood flow and blood pressure regulation. Semaglutide causes significant weight loss and can lower blood pressure, particularly during the early months of treatment. The optic nerve head is supplied by small perforating blood vessels that are particularly sensitive to pressure changes. A sudden drop in blood pressure — or episodes of lower blood pressure during sleep — could reduce perfusion of an already vulnerable optic nerve.

A second hypothesis involves rapid changes in blood sugar. In people with diabetes, the rapid improvement in glycaemic control that semaglutide produces can temporarily worsen diabetic retinopathy and affect retinal blood vessel function — a phenomenon already documented in the SUSTAIN-6 clinical trial. Whether this mechanism contributes specifically to NAION is not confirmed.

A third possibility is that the association is mediated partly by the weight loss itself rather than the drug directly. Rapid significant weight loss produces haemodynamic changes — changes in blood volume, pressure, and vessel tone — that could theoretically affect optic nerve perfusion in susceptible individuals. This would explain why the risk is higher in obesity patients losing larger amounts of weight.

What experts consistently emphasise is that the mechanism, whatever it is, does not appear to be a direct toxic effect of semaglutide on eye tissue. The eye itself is not being damaged by the drug — it is the blood supply to the optic nerve that is being affected, likely through haemodynamic changes associated with the medication’s broader systemic effects.

— Dr Joseph Rizzo, Director of Neuro-Ophthalmology, Mass Eye and Ear, Harvard Medical School

What to Do About This Risk

If you have risk factors — before or early in treatment

If you have one or more of the risk factors listed above — particularly sleep apnoea, significant vascular disease, or a previous episode of NAION — discuss the NAION risk specifically with your prescriber before starting or continuing semaglutide. A baseline eye examination with an ophthalmologist is a reasonable step for higher-risk individuals, not because there is a proven protective intervention but because it establishes a baseline and identifies whether you have the small disc anatomy that compounds risk.

Know the symptoms and act on them immediately

The single most important action any semaglutide user can take regarding NAION is to know what the symptoms are and to seek immediate eye care if they develop. NAION is time-sensitive. There is no proven treatment that fully restores vision once NAION has occurred, but early evaluation may identify the condition and prevent additional damage. Do not wait overnight. Do not book a GP appointment for the following week. Go to an emergency eye clinic or A&E the same day symptoms appear.

Continue taking your medication unless your doctor advises otherwise

The evidence does not support stopping semaglutide based on the NAION risk for the general population. The absolute risk is very low — up to 1 in 10,000 people. The cardiovascular and metabolic benefits of these medications for appropriate patients are substantial and well-established. The decision to continue or modify treatment should be made with your prescriber based on your individual risk profile, not based on media coverage of the litigation.

Putting the Risk in Perspective

The numbers deserve honest interpretation. A 4–7 times increased relative risk sounds alarming in isolation. In context it is more nuanced.

The baseline incidence of NAION in the general population is approximately 2–10 per 100,000 people per year. Even applying a 7-fold relative risk to the high end of that baseline gives an absolute risk of around 70 per 100,000 per year — which is 0.07%, or 7 in 10,000. The EMA’s official classification of the condition as affecting up to 1 in 10,000 is consistent with this range.

The JAMA 2025 study of 37 million patients found an incidence rate of approximately 14 cases per 100,000 person-years among semaglutide users — which is 0.014% per year. For comparison, the SELECT trial found semaglutide reduced major cardiovascular events — heart attack, stroke, cardiovascular death — by 20% in people with obesity without diabetes. These events occur in approximately 6–8% of high-risk patients over a three-year period. The magnitude of benefit substantially exceeds the magnitude of the NAION risk for most people taking these medications for appropriate indications.

This is not a reason to be dismissive of the NAION finding. It is a genuine safety signal that has been appropriately confirmed by regulators and appropriately communicated. But the risk-benefit calculation for the population of people who benefit from GLP-1 therapy strongly favours treatment for most individuals, with informed awareness of symptoms and appropriate monitoring for those with additional risk factors.

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