Pharmacist Raj Patel, known online as Pharmacist Health Raj, has warned that certain injectable medications carry a rare possibility of being linked to an eye condition that can cause lasting sight loss.
Affecting fewer than one in 10,000 people, the side effect may happen without pain, but the damage could become permanent and irreversible. The warning applies to drugs such as Ozempic, Wegovy and Mounjaro.
What is the rare side effect?
Patel said: "One rare cause [of vision loss] is reduced blood flow to a nerve at the back of your eye. It can cause lasting sight loss even without pain. America's medicines regulator has ordered a warning about a possible increased risk with GLP1 diabetes and weight loss medicines. These include Ozempic, Wegovy and Mounjaro."
Research published in JAMA Ophthalmology identified a statistical association between glucagon-like peptide-1 (GLP-1) receptor agonists and NAION, an uncommon condition that affects the optic nerve and may impair vision. Researchers emphasise that a direct cause-and-effect relationship has yet to be established, and the evidence remains inconclusive.
NAION typically presents with sudden, painless vision loss, often first noticed upon waking. Damage sustained by the optic nerve is frequently permanent and cannot be undone.
Regulator warnings and research
Ozempic is a prescription drug specifically licensed and intended for controlling blood sugar levels in adults with type 2 diabetes. Although weight loss may occur as a secondary side effect, it is not approved for use as a weight management treatment.
The US Food and Drug Administration (FDA) has ordered safety-labelling changes for all GLP-1 receptor agonist medications, including semaglutide (Ozempic and Wegovy) and tirzepatide (Mounjaro). The FDA has highlighted a potential increase in the risk of rare non-arteritic anterior ischemic optic neuropathy (NAION) and advises patients to report any sudden, painless vision loss or visual disturbances in one eye without delay.
Raj Patel states that those responsible for regulating drugs in the UK already issue warnings regarding semaglutide, the active ingredient found in Ozempic and Wegovy. The UK Medicines and Healthcare products Regulatory Agency (MHRA) has updated product information for semaglutide products (Wegovy, Ozempic, and Rybelsus), categorising NAION as a "very rare" side effect affecting up to 1 in 10,000 people.
What should patients do?
These safety warnings emerged following a 2024 Harvard study of nearly 17,000 patients that identified higher rates of this eye condition in individuals taking semaglutide compared with other medications. Regulators subsequently examined 126 clinical trials involving more than 134,000 patients and confirmed that rare cases had occurred across the entire GLP-1 drug group.
Large-scale studies of routine patient records also suggested a higher relative risk, though the actual likelihood of developing the condition remains extremely low, at approximately one additional case per 10,000 people each year. Health officials emphasise that this research points to a possible association rather than definitive proof, particularly because underlying health conditions, such as diabetes, can independently cause the eye condition.
While US regulators have issued a class-wide warning covering all GLP-1 medications, including both semaglutide (Wegovy) and tirzepatide (Mounjaro), UK guidance is currently more specific. In the UK, the MHRA has issued a formal safety alert for semaglutide products, while evidence regarding other drugs in the same class, including Mounjaro, remains under review.
As outlined in the video, the alert applies solely to semaglutide, not to Mounjaro (tirzepatide). Nevertheless, the MHRA advises anyone experiencing sudden vision loss while taking semaglutide to attend A&E immediately and to discontinue the medication should NAION be confirmed.
Patel said: "Not every vision change is caused by your medicine. But if you experience sudden sight loss, or rapidly worsening eye symptoms or vision problems, you need to go to casualty or A&E. Don't drive, don't stop the treatment yourself and tell the team what you take."
It is important never to stop essential medication abruptly without first seeking medical advice. Should you have any concerns, contact your GP.
