The MHRA's February 2026 Drug Safety Update records non-arteritic anterior ischaemic optic neuropathy (NAION) as a very rare reported risk of semaglutide — the active substance in Wegovy, Ozempic and Rybelsus — and advises urgent ophthalmological assessment if vision changes suddenly during treatment.
What the regulator published
On 5 February 2026 the MHRA issued Drug Safety Update volume 19, issue 7, recording that NAION has been very rarely reported in association with semaglutide across its licensed uses: type 2 diabetes (Ozempic, Rybelsus), weight management (Wegovy) and cardiovascular risk reduction. NAION affects the optic nerve head and typically presents as sudden, painless vision loss, usually in one eye. It is a leading cause of vision loss in adults. The MHRA classifies the risk as very rare.
The update followed a European review. The European Medicines Agency's Pharmacovigilance Risk Assessment Committee (PRAC) reviewed non-clinical data, trial data, post-marketing surveillance and the medical literature and concluded that NAION is a very rare side effect of semaglutide, potentially affecting up to 1 in 10,000 users. The World Health Organization has issued a corresponding alert to healthcare professionals and regulators.
What the regulator advises
For healthcare professionals
Patients who report sudden loss of vision, including partial loss, while taking semaglutide should be urgently referred for ophthalmological examination.
For patients
Sudden blindness, or eyesight that worsens very quickly, in one or both eyes during treatment should prompt urgent attendance at eye casualty or A&E. Regulators advise that semaglutide be stopped if NAION is confirmed.
Where semaglutide sits in the UK
Semaglutide is a licensed medicine in the UK, with different brand presentations authorised for different indications. Prescribing and supply rest on the MHRA marketing authorisation and, for NHS use, on NICE guidance such as NG28. Nothing in this article concerns the research-peptide market, where 'research use only' framing applies and human use is not sanctioned.
Why a licensed-medicine signal matters here
Peptide Data grades the research-peptide literature; this is a safety signal for a medicine that already holds a UK licence. The distinction is the point. It shows how a licensed GLP-1 receptor agonist is monitored after authorisation, through product-information updates and the Yellow Card scheme, and how a rare but serious signal is surfaced and acted on rather than left to the grey market. It also illustrates the gap between a licensed, monitored medicine and the unlicensed 'research' supply that imitates it.
Reporting and the Yellow Card scheme
Suspected adverse reactions to semaglutide or any other GLP-1 medicine should be reported to the MHRA through the Yellow Card scheme, by website, app or clinical IT system. Reports should include medical history, concomitant medicines, onset timing and treatment dates.
What remains uncertain
The signal is rare and the causal pathway is not fully characterised. NAION also occurs in people who have never taken a GLP-1 medicine, and risk factors are incompletely described. The MHRA's advice is precautionary and rests on the totality of the evidence rather than on a defined mechanism.
Evidence grade: NAION as a semaglutide risk
Very rare, regulator-confirmed adverse reaction (EMA PRAC conclusion; MHRA Drug Safety Update, February 2026).
This article is AI-researched and editorially reviewed. It is provided for research and educational purposes only and is not medical advice. Research peptides are not licensed for human consumption in the UK.