Drugs such as Ozempic, Wegovy, and Mounjaro (known as semaglutide and tirzepatide) have changed the way clinicians manage diabetes and obesity around the world.

Collectively known as GLP-1 agonists, these drugs mimic the hormone GLP-1. This limits both hunger and interest in food, helping users lose weight, and helps control blood sugar levels.

But two new studies show that people taking these drugs may have a small increased risk of serious eye conditions and vision loss. Here’s what you need to know if you’re taking or considering these medications.

Non-arteritic anterior ischaemic optic neuropathy, or NAION, is a rare but devastating eye condition that occurs when blood flow to the optic nerve is suddenly reduced or blocked. It’s also called an “eye stroke”. The exact cause of NAION remains unclear, and there are no current treatments available. People with diabetes are at increased risk of developing NAION.

Unlike other eye conditions that develop gradually, NAION causes a sudden, painless loss of vision. Patients typically notice the condition when they wake up and discover they’ve lost vision in one eye. Vision tends to worsen over a couple of weeks and slowly stabilises. Recovery of vision is variable, but around 70 per cent of people do not experience improvement in their vision. What has previous research shown?

A previous study from 2024 found that participants prescribed semaglutide for diabetes were four times more likely to develop NAION. For those taking it for weight loss, the risk was almost eight times higher. In June, the European Medicines Agency concluded NAION represented a “very rare” side effect of semaglutide medications: a one in 10,000 chance. However, recent studies suggest the risks may be lower than we first thought. In addition to NAION, there is also evidence to suggest GLP-1 drugs can worsen diabetic eye disease, also known as diabetic retinopathy.

This occurs when high blood sugar levels damage the small blood vessels in the retina, which can lead to vision loss.Studies also show that patients with heart conditions who better adhere to their medication prescriptions have lower risks of NAION than those who don’t. Doctors should discuss NAION risks during prescribing decisions and work with eye care providers to monitor regularly for diabetic eye disease. Patients need clear instructions to seek immediate medical attention for sudden vision loss and the need for regular eye examinations.

Aggressive treatment of sleep apnoea and other heart conditions may also help reduce NAION risks. But for now, there remains an ongoing need for more research to understand how GLP-1 medications can affect the eye.

(Flora Hui is with the University of Melbourne and Pete A Williams is from Karolinska Institutet)