WASHINGTON D.C.: The US Food and Drug Administration is requiring GLP-1 drugs for weight loss and diabetes, including Eli Lilly's Mounjaro and Zepbound and Novo Nordisk's Ozempic and Wegovy, to carry a warning about a potential increased risk of a serious eye condition.

The FDA said on November 9 that the drugs must add information to the "warnings and precautions" section of labeling about the potential increased risk of non-arteritic anterior ischemic optic neuropathy (NAION).

The condition is a common cause of sudden, painless vision loss, and may lead to permanent impairment of sight in some cases. It is caused by decreased blood flow to the front part of the optic nerve, but the underlying cause is not completely understood.

The health regulator said it has evaluated clinical trial data, animal data, and post-marketing data, including observational studies and case reports.

"FDA's drug safety communication applies to all medicines with GLP-1 RA activity and does not reference any findings specific to Lilly medicines. We are carefully evaluating the update and will respond to FDA promptly," said a Lilly spokesperson.

"Novo continues to believe the data do not establish a cause-and-effect relationship and we remain confident in the benefit-risk profile of our GLP-1 medicines," a spokesperson for Novo said.

"The FDA action may temporarily increase patient and investor concern, but the rarity of NAION and substantial weight, glycemic, cardiovascular, renal, and sleep apnea benefits should preserve a favorable benefit-risk profile and limit changes to prescribing," Citi analyst Geoff Meacham said.

Last year, the European Medicines Agency's safety committee said NAION may affect up to 1 in 10,000 people taking semaglutide, the active ingredient in Wegovy and Ozempic as well as in Novo's other diabetes drug Rybelsus, for at least one year. That was the first time a regulator had confirmed the side effect.

Four patients in Denmark, who experienced vision loss after using Novo's GLP-1 drugs, were granted compensation, the Danish Patient Compensation had said last year.

A large study published in 2025 tracked nearly 175,000 diabetic patients treated with semaglutide and an equal number taking non-GLP-1 medications. It found that the risk of NAION more than doubled after two years of treatment with a GLP-1 drug, compared to diabetes medicines from other classes.