The UK Medicines and Healthcare products Regulatory Agency (MHRA) has issued a warning to patients using semaglutide injections, marketed as Ozempic for diabetes and Wegovy for weight loss, because of a rare but serious side effect. According to The Times, taking the drug can reduce blood flow to the optic nerve, causing non-arteritic anterior ischemic optic neuropathy (NAION), which can lead to sudden loss of vision in one eye.
NAION occurs when the front part of the optic nerve does not receive enough blood, usually causing painless loss of vision in one eye. Affected patients describe this situation as blurred or cloudy vision. The MHRA reported three cases of NAION in patients using semaglutide. Although the risk is low — about one in 10,000 people who use the drug could be affected — the agency stresses the importance of monitoring symptoms.
“Patient safety is our top priority. Although the risk of NAION is extremely small, patients and healthcare professionals should be aware of the sudden loss of vision in one eye and report to an emergency eye service immediately,” said MHRA safety director Alison Cave.
In total, around two million people in the UK use these slimming injections, with many switching from Mounjaro (tirzepatide) to Wegovy after the drug’s price rise in September 2025.
The MHRA also warned last week that these drugs can cause acute pancreatitis, a serious inflammation of the pancreas that can be fatal. Other more common side effects include nausea and vomiting, but severe cases such as NAION and pancreatitis remain extremely rare.
