People taking Ozempic and similar drugs may have to keep an eye out for an unexpected side effect. Health officials in Europe are looking into whether these diabetes and weight loss treatments could raise the risk of a rare but serious disorder that can cause blindness, following recent reports showing a possible association.
On Monday, the Danish Medicines Agency announced that it would ask health officials at the European Union to investigate if GLP-1 medications can potentially cause non-arteritic anterior ischemic optic neuropathy, or NAION. Studies this year from researchers in the U.S., and now Denmark, have suggested that GLP-1 users face a greater risk of NAION. At this point, however, it’s still not clear whether there’s a causative link between the two, and the condition appears to be very rare even among GLP-1 users.
NAION is caused by a loss of blood flow to the optic nerve, which then results in sudden and often permanent vision loss. Not much is known about why it happens, though some likely risk factors include age, high blood pressure, and sleep apnea.
Ophthalmologists at Harvard Medical School and Mass Eye and Ear were the first scientists to publicly highlight the potential connection between NAION and GLP-1s. In July, they published a study showing that people taking semaglutide (the active ingredient in Ozempic and Wegovy) for their diabetes or obesity were more likely to develop NAION than similar patients taking other drugs over a three year period.
This month, two separate teams at the University of Southern Denmark released the preliminary results of their studies on the topic (one study has been accepted for publication at a peer-reviewed journal, the other is undergoing peer review). Both studies tracked the prevalence of NAION among people in Denmark taking semaglutide for diabetes compared to other medications (one study additionally looked at residents in Norway). As with the earlier U.S. study, they found a noticeably higher risk of NAION in those taking semaglutide.
The Danish Medicines Agency has also been keeping track of a possible rise in NAION cases, via adverse event reports filed to it by doctors and patients (most every country, including the U.S., has a similar system). But it wasn’t until these latest studies that the agency felt compelled to go further. It is now asking the EU’s Pharmacovigilance Risk Assessment Committee (PRAC) to review the Danish studies and other data in order to determine whether NAION is a genuine side effect of semaglutide use.
“In the past six months, we have evaluated reports and studies involving the serious eye condition known as NAION in collaboration with our European colleagues. These new register-based studies provide comprehensive data from Danish and Norwegian registers that the European Pharmacovigilance Risk Assessment Committee may now consider,” said Line Michan, director of pharmacovigilance at the DMA, in a statement Monday. “Therefore, we will now request PRAC to assess the new studies.”
While these studies do add more weight to the idea that GLP-1 medications can trigger NAION, they are still far from definitive proof. Observational, retrospective data alone can’t demonstrate a cause-and-effect relationship between any two factors. Other types of studies, such as placebo-controlled clinical trials, studies tracking real-life GLP-1 users proactively, or even lab studies with animals, would likely be needed to confirm a genuine increased risk of NAION from these drugs.
Researchers and health officials have also been careful to point out that any such higher risk will probably still be very small. Though NAION is the second most common cause of blindness due to optic nerve damage, following glaucoma, it’s a rare disorder. In the U.S., it’s estimated that there are several thousand new cases of NAION every year.
The earlier U.S. study found that semaglutide was associated with a sevenfold higher risk of NAION. But the larger, likely more representative Danish studies instead found a two- to threefold higher risk. The Danish researchers estimated that for every 10,000 people treated with semaglutide in a year, somewhere between 1.5 and 2.5 extra cases of NAION might occur (assuming a real link, of course). Up through early December, the DMA has received 19 reports of NAION potentially tied to semaglutide, dating back to July 2024.
The benefits of GLP-1 therapy are also likely to outweigh the potential danger of NAION for most eligible patients. Poorly treated diabetes can itself lead to vision issues, for instance. But given how serious and life-changing NAION can be, even a small increased risk of it is still worth paying attention to. By studying this link further, it’s possible that researchers will find other factors that affect a person’s chance of developing NAION while taking a GLP-1 drug, and that could help prevent cases in the future. Someone at higher risk might be advised to take a different diabetes drug, for instance. For now, we’ll just have to wait and see where the dust settles.
GLP-1 drugs like Ozempic are known to cause common side effects like nausea and constipation, though these tend to fade over time. In the years since being widely released to the public, the drugs have been associated with serious, but rare complications like gastroparesis (stomach paralysis). Some studies have also flagged potential issues with their use that have not been supported by later research, such as a higher risk of suicide.