Patients taking Wegovy have almost five times the risk of sudden vision loss than those taking Ozempic, a large-scale study has found.
Glucagon-like peptide 1 receptor agonist (GLP-1 RA) medications, such as semaglutide (sold as Wegovy, Ozempic, and Rybelsus) and tirzepetide (sold as Mounjaro), help lower blood sugar levels, slow digestion, and reduce appetite, and have been linked to lower risks of heart attack, fewer drug overdoses, and other health benefits.
But one study, published in the British Journal of Ophthalmology, found that patients taking Wegovy for weight loss were five times more likely to develop non-arteritic anterior ischemic optic neuropathy (Naion) than the diabetes drug Ozempic, while men had a three times higher risk than women.
These “eye hits” cause sudden and usually permanent vision loss (pdf) due to reduced blood flow to the optic nerve.
Although rare, affecting about one in 10,000 people taking semaglutide, there was “a potential dose-dependent safety concern” for the drug, the study found.
Wegovy, Ozempic, and Rybelsus, made by Novo Nordisk, contain semaglutide, but they have different dosages and formulations.
Dr. Edward Margolin, of the University of Toronto’s department of ophthalmology and one of the authors of the research, said Naion would likely be “a real side effect” of semaglutide, and that faster, faster or more aggressive weight loss would likely “increase the risk” of Naion.
The study examined side effect reports submitted to the US drug regulator, the Food and Drug Administration, through its adverse event reporting system between December 2017 and December 2024.
Canadian researchers compared any reports of Naion associated with up to 2 mg of weekly injectable Ozempic for type 2 diabetes; up to 2.4 mg weekly of injectable Wegovy for obesity (the highest approved dose) and one daily tablet of Rybelsus for type 2 diabetes. They also examined the reported side effects of tirzepatide (Mounjaro).
The study found that Wegovy had the strongest association with sudden vision loss. In contrast, the authors did not find an increased risk with Rybelsus tablets or tirzepatide.
The authors said the high doses of Wegovy and the fact that the injections worked faster could explain why the association was stronger. In contrast, the limited absorption and slower absorption of Rybelsus tablets likely accounted for the lack of a detectable link, they said.
The findings came after the UK’s Medicines and Healthcare products Regulatory Agency published an update on drug safety in February, warning of the risk from Naion. This followed similar warnings from the European medicines regulator.
Dr Alison Cave, chief safety officer at the MHRA, said: “The risk from Naion in patients prescribed semaglutide is extremely low. However, as with all medicines, patients and prescribers should be aware of the symptoms of possible side effects, even if the risk is very small, to ensure patients receive appropriate treatment quickly if they occur.”
Samantha Mann, consultant ophthalmologist and diabetic eye screening lead at the Royal College of Ophthalmologists, said: “This study was based on reported side effects and therefore cannot prove causality or determine how common this problem really is. However, an increase in this form of optic nerve ‘stroke’ has not been widely seen in routine clinical practice at St Thomas’ in London, where I work. Therefore, further studies are needed to clarify whether this increased risk It’s really real.”
A Novo Nordisk spokesperson said: “Patient safety is our top priority and we take any reports of adverse events arising from the use of our medicines very seriously. We work closely with authorities and regulatory bodies around the world to continually monitor the safety profile of our products.”
The EU package inserts for Wegovy, Ozempic and Rybelsus had been updated to include Naion, they added, but “based on the totality of the evidence, we concluded that the data did not suggest a reasonable possibility of a causal relationship between semaglutide and Naion and Novo Nordisk believes that the benefit-risk profile of semaglutide remains favorable.”
