Hundreds of consumers are suing manufacturers of GLP-1 weight-loss drugs—Novo Nordisk (Ozempic, Wegovy) and Eli Lilly (Mounjaro, Zepbound)—alleging the medications increase the risk of NAION, a rare eye condition that causes sudden vision loss through reduced blood flow to the optic nerve. The lawsuits highlight a serious concern because NAION has no available treatment and can result in profound vision loss, particularly in adults over 50 where it is the most common cause of acute optic nerve injury. The pharmaceutical companies have disputed the allegations, with Novo Nordisk calling the lawsuits meritless and citing company-funded research showing no increased risk.

Research findings remain inconclusive but suggestive of a possible link. A 2025 study of 37 million adults published in JAMA Ophthalmology found a modest increase in NAION risk with semaglutide use, whilst a 2024 Harvard Medical School study reported approximately fourfold higher relative risk among type 2 diabetes patients prescribed semaglutide, though absolute risk remained very low. Both studies were observational in nature and could not prove causation. The FDA is reviewing the evidence but has not concluded that semaglutide causes NAION or issued a safety warning, whilst the European Medicines Agency determined sufficient evidence exists to add NAION as a "very rare" adverse reaction to semaglutide labelling. Complications in establishing causation arise because many GLP-1 users have diabetes or obesity, which are themselves established risk factors for NAION.