The US Food and Drug Administration (FDA) has issued a new warning on GLP-1 medications – which can facilitate weight loss – over a rare eye condition that could lead to sudden and permanent blindness.

On Monday, the FDA announced that it is requiring all GLP-1 medications – including Novo Nordisk’s Ozempic and Wegovy, Eli Lilly’s Mounjaro and Zepbound, as well as Sanofi’s Soliqua – to include information about the potential risk of nonarteritic anterior ischemic optic neuropathy, also known as NAION, on warning labels.

NAION is a rare condition involving sudden reduction of blood flow to the optic nerve, in turn resulting in acute, painless, decreased vision in one eye, including permanent vision loss, the FDA warned.

Common risk factors of NAION include diabetes, smoking, hypertension, as well as hypercholesterolemia. It is the most common cause of acute optic nerve injury in individuals over 50 years old, with an annual average of 2.3 to 10.2 cases out of 100,000 people above that age. There is for now no treatment to reverse vision loss from NAION.

According to the FDA, the agency began looking at potential links between GLP-1s and NAION after a 2024 study published in the journal JAMA Ophthalmology. The study found an increased risk of NAION among patients using GLP-1 medications.

Despite identifying several limitations of the study, the FDA said it “determined that further assessment of the potential increased risk for NAION was warranted”.

The agency proceeded to review 126 clinical trials involving over 134,200 patients and identified 15 probable NAION cases, including 10 among GLP-1 patients; five in patients receiving placebo; and none in patients who were on glucose-lowering medications that were not GLP-1.

The FDA found a NAION incidence rate of 6.4 cases per 100,000 person-years among GLP-1 patients, compared to 3.8 cases among patients on placebo or alternative glucose-lowering medications.

“NAION cases have been reported for all currently marketed GLP-1 RA products,” the FDA said. “FDA concluded that there is a potential increased risk of rare NAION events in patients taking GLP-1 RAs.

“Based on these findings, FDA is requiring that application holders add information about the risk for NAION to the Warnings and Precautions section of labeling of all GLP-1 RAs.”

In response to the FDA announcement, a Novo Nordisk spokesperson told the Guardian that the pharmaceutical company “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.”

The statement also said: “Patient safety is a top priority for Novo, and we continue to monitor the safety of our medicines, review new research and work with health authorities around the world.”

The Guardian has reached out to Eli Lilly and Sanofi for additional comment. Eli Lilly had previously said it is aware of publications on the risk of NAION among GLP-1 patients.

GLP-1 medications are mainly used by people with type 2 diabetes managing their blood sugar – or glucose – levels. Some of the medications are also used to help treat obesity. And some have been known to seek access to such drugs for cosmetic reasons rather than legitimate medical ones.

The FDA’s announcement comes amid warnings from the Netherlands-based non-profit Access to Medicine Foundation that the pharmaceutical focus on GLP-1 weight-loss drugs risks putting global insulin supply at risk.