The US Food and Drug Administration has told the makers of every GLP-1 receptor agonist, the drug class that includes semaglutide and tirzepatide, to add a warning about a potential increased risk of non-arteritic anterior ischaemic optic neuropathy (NAION), a rare condition that causes sudden vision loss in one eye. The absolute risk is very small and causation is not established. But the warning matters for the millions of people, in India and elsewhere, now taking these drugs for diabetes and obesity.
In a Drug Safety Communication dated 9 November, the FDA said it is requiring manufacturers to add information about “the potential increased risk of NAION” to the Warnings and Precautions section of their labelling. The requirement applies to the whole class of glucagon-like peptide-1 receptor agonists (GLP-1 RAs). The FDA noted that NAION cases have been reported with every GLP-1 RA currently on the US market.
The drugs listed include:
- Semaglutide: Ozempic, Wegovy and the oral Rybelsus.
- Tirzepatide: Mounjaro and Zepbound, which also act on the GIP receptor.
- Older injectables: liraglutide (Victoza, Saxenda), dulaglutide (Trulicity) and exenatide.
- Combinations: Xultophy and Soliqua, which pair a GLP-1 RA with insulin.
- Oral newcomer: orforglipron (Foundayo), approved in the US this year.
What is NAION?
NAION is a stroke-like event at the front of the optic nerve, where it leaves the eye. Blood flow to the nerve head falls, the tissue swells and nerve fibres are damaged. Patients typically notice sudden, painless loss of vision in one eye, often on waking. They may see a blind spot, blurring of central vision or dull, washed-out colours. There is no proven treatment, and lost vision often does not return.
NAION is rare. The FDA cites a background rate of 2.3 to 10.2 cases per 100,000 people a year among adults over 50. Its recognised risk factors overlap heavily with the conditions GLP-1 drugs treat: diabetes, high blood pressure, sleep apnoea, smoking, anaemia and kidney disease. This overlap is precisely what makes the drugs’ own contribution hard to measure.
The evidence the FDA weighed
The concern first drew wide attention in July 2024, when a study from Massachusetts Eye and Ear in JAMA Ophthalmology reported a markedly higher risk among patients prescribed semaglutide. The FDA says that study had “several limitations”, but judged further assessment warranted. Its review drew on several lines of evidence:
- Randomised trials: a meta-analysis of 126 trials with 134,253 participants and 288,879 person-years of follow-up found 15 probable NAION events, 10 among people on GLP-1 RAs and 5 on placebo. That corresponds to 6.4 against 3.8 cases per 100,000 person-years. With so few events, the comparison is statistically fragile.
- The FDA’s Sentinel system: in adults with type 2 diabetes from 2019 to 2024, NAION incidence was 30–32 per 100,000 person-years on GLP-1 RAs, 31 on SGLT-2 inhibitors and 26 on DPP-4 inhibitors. The hazard ratio was 1.19 against SGLT-2 inhibitors, not statistically significant, and 1.43 against DPP-4 inhibitors (95% confidence interval 1.02–2.01).
- Published observational studies: these “consistently reported” a higher risk than with DPP-4 or SGLT-2 inhibitors.
- Animal studies: no mechanism has been identified.
The FDA does not say that GLP-1 drugs cause NAION. It describes a “potential” increased risk of a “rare” event whose cause “is not completely understood”. In absolute terms, even if the trial figures reflect a true effect, the excess is a few cases per 100,000 people treated for a year.
Why the signal is hard to pin down
Three features of NAION make it difficult to study. It is rare, so even very large trials record only a handful of cases. It is diagnosed clinically, so ophthalmologists can disagree about whether a given case qualifies; the FDA counted only “probable” events. And the people most likely to be prescribed GLP-1 drugs are, by definition, the people most at risk of NAION. Observational studies try to adjust for this by comparing GLP-1 users with patients on other diabetes drugs, but they cannot fully remove the bias. That is why the estimated risk shrinks against some comparators and persists against others.
Regulators converge
Europe moved first. In June 2025, the European Medicines Agency’s safety committee, PRAC, concluded that NAION is a “very rare” side effect of semaglutide, affecting up to 1 in 10,000 users, according to Ophthalmology Times. The FDA’s action is broader: it applies to the entire class, not to semaglutide alone.
What patients and doctors should do
The FDA’s advice is practical:
- Patients: seek medical care immediately for sudden vision loss in one eye, blind spots, tunnel vision, blurred central vision or colour changes. They should not stop treatment without first talking to their clinician. Those who have previously had NAION should discuss whether to continue, because recurrence is a risk.
- Clinicians: refer suspected cases promptly to an ophthalmologist, and “consider discontinuing the GLP-1 RA in patients who develop NAION, unless the benefits of treatment clearly outweigh the risk”.
For most patients, the benefits of GLP-1 drugs, which include better blood-sugar control, weight loss and, for some, proven reductions in heart attacks, strokes and kidney disease, far outweigh a risk of this size. Rapid falls in blood sugar can also affect the eyes in other ways, which is one reason eye checks are already recommended for people with diabetes.
The Indian angle
India has the world’s second-largest population of adults with diabetes, and use of GLP-1 drugs has grown quickly. Semaglutide’s patent expired in India in March 2026, and lower-cost generic versions followed. Tirzepatide and semaglutide are also widely promoted for weight loss. NSH found no statement from the Central Drugs Standard Control Organisation (CDSCO) in response to the FDA’s action. Indian labelling for these products is set by CDSCO, not the FDA, and may not change automatically.
The practical message for Indian patients is the same as for American ones: know the warning signs, report sudden vision changes immediately and do not stop treatment without medical advice. Self-medication with GLP-1 drugs bought without supervision carries additional risks.
