The global boom in GLP-1 medicines is facing a fresh safety question as regulators, researchers and US courts examine a possible link between semaglutide and non-arteritic anterior ischaemic optic neuropathy (NAION), a rare condition that can cause sudden vision loss.
The issue gained renewed attention after Novo Nordisk cited clinical-trial data showing a small number of confirmed NAION cases among people taking its GLP-1 medicines. At the same time, several studies using real-world patient data have reported an association between. European regulators have classified the condition as a very rare side effect of semaglutide.
NAION occurs when blood flow to the optic nerve is disrupted, generally causing sudden, painless vision loss in one eye.
In June 2025, the European Medicines Agency’s safety committee concluded that NAION is a very rare side effect of semaglutide, potentially affecting up to one in 10,000 people.
The regulator said several large epidemiological studies suggested that adults with type 2 diabetes taking semaglutide had roughly twice the risk of NAION compared with those not taking the drug.
The UK medicines regulator later added the warning to product information and advised patients with sudden or rapidly worsening vision to seek urgent medical attention.
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Novo Nordisk’s pooled analysis presents a different picture from some observational studies.
The analysis covered 96,829 participants and more than 205,000 participant-years across randomised trials involving GLP-1 medicines and placebo. Researchers identified three confirmed NAION cases among GLP-1-treated participants and five among those receiving placebo.
The incidence was around three cases per 100,000 participant-years in the GLP-1 group, compared with about six per 100,000 in the placebo group. Novo said the randomised trial data did not show an increased incidence of NAION among people receiving GLP-1 treatment.
Several observational studies have reported a higher incidence of NAION among semaglutide users, particularly people with type 2 diabetes.
A 2026 systematic review and meta-analysis covering more than 14 million people with type 2 diabetes found an increased risk of NAION among semaglutide users. Another 2026 meta-analysis of eight observational cohorts involving nearly 5.9 million people also reported a higher risk.
However, observational studies can show an association without proving that semaglutide caused the condition. The contrast between these findings and Novo Nordisk’s randomised-trial data remains central to the safety debate.
The issue has also moved into US courts. Federal lawsuits alleging that GLP-1 medicines caused NAION have been consolidated into multidistrict litigation in the Eastern District of Pennsylvania.
A September 1, 2026 report from the Judicial Panel on Multidistrict Litigation lists 216 pending actions. The litigation involves allegations concerning medicines made by Novo Nordisk and Eli Lilly and addresses questions around drug development, testing, regulatory history, promotion and labelling. The consolidation is a procedural step and does not establish that the medicines caused NAION.
The scrutiny comes as Novo Nordisk and Eli Lilly compete in the rapidly expanding diabetes and obesity medicines market. Novo’s semaglutide products include, while Eli Lilly’s tirzepatide medicines include Mounjaro and Zepbound.
The evidence so far remains mixed. Novo’s randomised clinical-trial analysis found no increased incidence of NAION compared with placebo, while regulators and observational studies have identified a potential association. The EMA’s conclusion means NAION is formally recognised as a very rare adverse effect of semaglutide in Europe, with treatment advised to stop if NAION is confirmed.
For now, the evidence does not establish that GLP-1 medicines cause NAION, but the potential eye risk remains under regulatory, scientific and legal scrutiny.
