The drug firms behind blockbuster jabs like Wegovy, Mounjaro and Ozempic are facing at least 90 legal claims from patients who say the drugs left them with permanent vision loss.
Slimmers in the US say the injections caused a condition that cuts off blood supply to the optic nerve, often referred to as an 'eye stroke'.
The appetite-suppressing drugs are thought to damage the tiny blood vessels that feed the back of the eye, although this has not been fully proven.
However the risk is recognised by the UK's Medicines and Healthcare products Regulatory Agency (MHRA), who earlier this year issued a warning about the injections' link to the condition - named non-arteritic anterior ischaemic optic neuropathy, or NAION.
Meanwhile research published in 2024 found users of semaglutide - the ingredient in Ozempic and Wegovy - were around four times more likely to develop the problem than those taking other diabetes treatment.
However other experts have questioned the validity of the claims, arguing that there is little scientific evidence to prove the jabs cause the eye condition.
The makers of Wegovy and Mounjaro are facing at least 90 legal claims from patients claiming the jabs gave them a condition that can cause permanent blindness
Just shy of 100 lawsuits have been filed against Novo Nordisk - the makers of Wegovy and Ozempic - since 2025 by personal-injury firm Weitz and Luxenberg, according to the Wall Street Journal (WSJ).
All of the patients are said to have developed NAION while using the drugs, known as GLP-1 agonists.
One claimant, 53-year-old Michelle Fennell, told the newspaper that she began experiencing blurred vision around six months after she started Ozempic.
At the time, she was using the injection for her type 2 diabetes, a disease the drug is approved to treat in the US and the UK.
Ms Fennell said her right eye began to feel heavy and her peripheral vision suddenly weakened. Her doctor diagnosed NAION two weeks later.
'[The doctor] said right away, stop taking Ozempic,' Fennell said. 'I was shocked.'
NAION, which affects around 1,400 to 7,000 people in the UK every year, is an incurable condition that develops when blood flow to the optic nerve, which carries images from the eye to the brain, is reduced or blocked.
This deprives the nerve of oxygen, causing sudden, and often permanent, vision loss.
Studies have suggested that those most at risk of the condition include older people, smokers and those with diabetes and high blood pressure.
'We have not had enough data yet to look at how the addition of GLP-1 medications compounds each of these risks,' Drew Carey, associate professor of clinical ophthalmology and neurology at Johns Hopkins Medicine, told the BMJ.
'But the best estimates thus far suggest a twofold increase in risk with these medications, and that typically only occurs in patients at high risk.'
Another US claimant, Jay Vandegriff, was also taking Ozempic for type 2 diabetes, having been prescribed the jab in 2023.
What are the warning signs of NAION?
Most people with NAION experience a sudden change in vision.
Because the condition is usually painless, it can be easy to miss the early signs.
Symptoms often include a blurred, dim or dark patch in one eye.
Source: NHS
Around a year later, the now 69-year-old began noticing changes to his vision, which he thought were a smudge on his glasses.
After cleaning them, however, he realised the problem was with his eyes.
Soon after, he was diagnosed with NAION, which he says has taken two-thirds of the sight in his left eye.
'It's affecting every minute of every day,' he told the WSJ. 'I'd almost pay anything to get my eyesight back.'
Separately, several more claims have been lodged against Eli Lilly - the makers of Mounjaro - but these are said to be far fewer.
The current proceedings are in the US, but they follow a combined payout of more than £1.1million given to 27 Danish patients after they developed NAION following injections of Ozempic and Wegovy.
Novo Nordisk said it is not involved in those cases and maintains that the payouts do not prove the drugs caused the condition.
A spokesman also said the legal proceedings against it in the US lack merit, adding that it is strongly defending them.
'There are no indications that we should really be worried about NAION,' Dr Tina Vilsboll, senior medical officer at Novo and lead author on the study, told the WSJ.
'I do not see causality.'
In a statement to the British Medical Journal Liz Skrbkova, the drugmaker's head of US media and stakeholder relations, highlighted the results of a company-funded analysis published in the British Journal of Ophthalmology earlier this year.
It found no increased incidence of NAION in patients taking its drugs when compared with those receiving a placebo.
However, separate research has found a link.
A large analysis published in JAMA Network Open last year found semaglutide and tirzepatide users were 76 per cent more likely to develop the condition compared to those taking other diabetes medicines. Researchers stressed, however, that the overall risk was low.
In an accompanying comment on the 2025 study, scientists wrote that the results could 'theoretically be linked to rapid improvement in glycemia', which is the term for blood sugar levels in the body.
Crucially, NAION is already up to 10 times more common in people with type 2 diabetes, affecting between 11 and 82 per 100,000 patients a year, according to the MHRA.
Experts say it is therefore difficult to separate the exact effects of the drugs from those of the disease they are often prescribed to treat.
'Figuring out whether the medication caused one person's case is very difficult... and ultimately that's what the courts are being asked to figure out,' Kevin Gendreau, an obesity medicine expert at Signature Healthcare in Massachusetts, told the British Medical Journal.
'[NAION] is something physicians and patients should be aware of, and it warrants further study.
'However, I don't think it's something that should cause all patients to panic.'
An Eli Lilly spokesman told the Daily Mail: 'Lilly is aware of publications on the potential risk of NAION in patients prescribed certain GLP-1 medicines, including statements by leading consensus organizations.
'We encourage healthcare professionals to exercise their own clinical judgment to evaluate this external literature.'
The company said patient safety is its 'top priority' and that it is in ongoing discussions with regulators about safety issues, including eye problems.
'If anyone is experiencing side effects when taking a Lilly medicine, they should talk to their doctor or other healthcare professional,' the spokesman added.
A Novo Nordisk spokesman said: 'Novo believes the personal injury lawsuits filed in the U.S. are without merit and is vigorously defending them.'
The company said it is aware of reports linking NAION and semaglutide and is investigating them, but that a 'causal relationship between semaglutide and NAION has not been established'.
'Patient safety is a top priority for Novo and we take all reports of adverse events associated with our medicines very seriously, collaborating closely with health authorities and regulatory bodies worldwide,' the spokesman added.