A large-scale study has found that patients taking Wegovy have nearly five times the risk of sudden sight loss compared to those on Ozempic. The research, published in the British Journal of Ophthalmology, examined reports of non-arteritic anterior ischemic optic neuropathy (Naion), an 'eye stroke' that causes sudden and usually permanent vision loss due to reduced blood flow to the optic nerve.
The study analysed side-effect reports submitted to the US Food and Drug Administration between December 2017 and December 2024. Canadian researchers compared reports associated with Ozempic (up to 2mg weekly), Wegovy (up to 2.4mg weekly), Rybelsus tablets, and tirzepatide (Mounjaro). Wegovy showed the strongest association with Naion, while no increased risk was found with Rybelsus or tirzepatide.
Dr Edward Margolin, from the University of Toronto and a study author, said Naion is likely a real side-effect of semaglutide, the active ingredient in Wegovy, Ozempic, and Rybelsus. He suggested that faster, more aggressive weight loss may increase the risk. The study noted a potential dose-dependent safety concern, although Naion is rare, affecting around one in 10,000 semaglutide users.
The UK Medicines and Healthcare products Regulatory Agency issued a drug safety update in February warning about the risk of Naion. Dr Alison Cave, MHRA chief safety officer, emphasised that the risk is extremely low but urged patients and prescribers to be aware of symptoms. However, Samantha Mann, a consultant ophthalmologist, cautioned that the study relied on reported side-effects and cannot prove causation, adding that such cases have not been widely observed in her clinical practice at St Thomas' Hospital in London.
A spokesperson for Novo Nordisk, the manufacturer, stated that patient safety is a top priority and that EU patient leaflets have been updated to include Naion. However, they concluded that the data do not suggest a reasonable possibility of a causal relationship and that the benefit-risk profile of semaglutide remains favourable.
