Ozempic, Mounjaro and other weight-loss drugs linked to rare but serious eye conditions

By Flora Hui and Pete A Williams for The Conversation

Melbourne: 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 published today 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.

What damage can occur?

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. In a first for medicines regulators, the agency now requires product labels to include NAION as a documented risk.

However, the 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.

It may sound counterintuitive, but rapid blood sugar reductions can also destabilise the fragile blood vessels in the retina and lead to bleeding.

What do the new studies say?

Two newly published studies investigated people with type 2 diabetes living in the United States over two years. The studies looked at the medical records of 159,000 to 185,000 people.

One study found that semaglutide or tirzepatide was associated with a more modest risk of developing NAION than previously thought. Of 159,000 people with type 2 diabetes who were taking these drugs, 35 people (0.04 per cent) developed NAION, compared with 19 patients (0.02 per cent) in the comparison group.

The researchers also found an increased risk of developing “other optic nerve disorders”. However, it’s unclear what kind of optic nerve disorders this includes, as the medical record codes used didn’t specify.

Counter to this, the second study did not find an increased risk of NAION among those taking GLP-1 drugs.

However, the researchers found a small increase in the number of people developing diabetic retinopathy in those prescribed GLP-1 drugs.

But overall, participants on GLP-1 drugs experienced fewer sight-threatening complications related to their diabetic retinopathy and required less invasive eye treatments compared to the group taking other diabetes medications.

Further studies are still needed to understand how GLP-1 drugs can lead to eye complications. A current, five-year clinical trial is studying the long-term effects of semaglutides and diabetic eye disease in 1,500 people, which should tell us more about the ocular risks in the future.

What does this mean for people taking GLP-1 drugs?

NAION is a serious condition. But we need to strike a balance between these (and other) risks and the benefits of GLP-1 medications in diabetes care, obesity treatment, reducing heart attack risks and extending lives.

The key lies in informed decision-making and identifying different levels of risk.

People with multiple NAION risk factors – such as sleep apnoea, high blood pressure and diabetes – should undergo careful consideration with their treating doctor before starting these medications.

“Crowded” optic nerve heads are also a risk factor for NAION. This is an anatomical feature where blood vessels at the optic nerve head are tightly packed together. People with crowded optic nerve heads should also undergo careful consideration before starting GLP-1 medications.

Although NAION can strike without warning, regular comprehensive eye examinations with your optometrist or ophthalmologist still serve important purposes. They can detect other drug-related eye problems, including worsening diabetic retinopathy, and can identify patients with crowded optic nerve heads. It’s also important to tell them if you are taking GLP-1 medications so they can keep a close watch on your eye health.

Emerging research also suggests that improving your heart health might help reduce the risks of developing NAION. This includes proper management of high blood pressure, diabetes and cholesterol – all conditions that compromise the small blood vessels feeding the optic nerve.

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 Research Fellow, Centre for Eye Research Australia and Honorary Fellow, Department of Surgery (Ophthalmology), The University of Melbourne

Pete A Williams is Ulla and Ingemar Dahlberg Professor in Vision Science, Research Group Leader, Karolinska Institutet