NAION: what it is, and how big the risk really is
NAION — non-arteritic anterior ischemic optic neuropathy — is a sudden, usually painless loss of vision in one eye caused by reduced blood flow to the front of the optic nerve. It is uncommon in the general population and tends to affect people with a “crowded” optic disc, sleep apnea, or vascular risk factors.
The story that reached the headlines started with a July 2024 study in JAMA Ophthalmology (Hathaway and colleagues at Massachusetts Eye and Ear). It reported a hazard ratio of about 4.3 for NAION with semaglutide among people with type 2 diabetes, and about 7.6 among people with overweight or obesity. Those numbers sound alarming — but the study drew everyone from a single tertiary referral neuro-ophthalmology clinic (a highly selected group, not a cross-section of the public), the confidence intervals were very wide, and the authors explicitly stated it cannot establish that semaglutide causes NAION. A referral-clinic hazard ratio overstates absolute risk for the general population — it is a signal worth investigating, not a measure of your personal risk.
The number that matters for you: after reviewing the wider evidence, the EMA (June 2025) put the effect at roughly a 2-fold relative increase on a very small baseline — on the order of one to two extra NAION cases per 10,000 person-yearsof treatment, which is why it is labeled “very rare.” That is a very different picture from “4x/7x.”
What the regulators did — and did not — do
It is easy to assume a warning was added everywhere. The precise, current picture:
- EMA (Europe), June 2025: the safety committee (PRAC) concluded NAION is a “very rare” side effect of semaglutide medicines and recommended the product information be updated to say so, advising that semaglutide be stopped if NAION is confirmed.
- WHO, June 2025:recommended NAION be added to the medicines' risk-management plan.
- US FDA, as of mid-2026: has not added NAION to the Ozempic or Wegovy label. US labeling can change, so ask your prescriber for the current status rather than assuming.
Diabetic retinopathy: a different, older issue
Separate from NAION is diabetic retinopathy — damage to the retina's blood vessels from long-standing high blood sugar. In the SUSTAIN-6 trial (NEJM, 2016), retinopathy complications were more common with semaglutide (3.0%) than placebo (1.8%). The imbalance was concentrated in people who already had retinopathy, were on insulin, and experienced a rapid fall in HbA1c. This “early worsening” with fast glucose lowering is well known across diabetes treatments — not something unique to semaglutide, and not a reason for people without retinopathy to worry.
Because of this, if you have existing diabetic eye disease your clinician may arrange an eye exam around the time you start and may lower your blood sugar more gradually. A dedicated 5-year trial designed specifically to answer this question, FOCUS, is ongoing, with results expected around 2027— so today's guidance is precautionary, not a final verdict.
Tirzepatide (Mounjaro / Zepbound)
A dedicated retina substudy within tirzepatide's cardiovascular program — one thatincluded patients who already had diabetic retinopathy — did not show increased retinopathy progression versus a comparator over about three years. That is reassuring, though some newer real-world reports raise the possibility of early worsening with rapid glucose lowering (as seen with other agents). No specific NAION signal has been established for tirzepatide — but that reflects less data, not proven safety. The sensible approach is the same: report sudden vision changes promptly.
What to actually do
Treat sudden vision change in one eye as urgent
Sudden or rapidly worsening vision, dimming, or a dark spot — especially in one eye and usually painless — warrants prompt evaluation by an eye specialist. Don't wait it out.
If you have diabetic retinopathy, tell your prescriber
Existing retinopathy, insulin use, and a fast HbA1c drop are the higher-risk combination. An eye exam around starting, plus a steadier glucose reduction, are reasonable precautions.
Don't stop the medication on your own
Stopping abruptly has its own risks. If you're worried about your eyes, contact your prescriber and an ophthalmologist so the cause can be assessed properly.