The Brazilian Health Regulatory Agency (Anvisa) is investigating 13 reports of non-arteritic anterior ischemic optic neuropathy (NAION) in patients using glucagon-like peptide-1 (GLP-1) receptor agonists. The condition causes a sudden and permanent loss of vision due to restricted blood flow to the optic nerve.
The Scope of the Anvisa Investigation
The reports involve a range of high-profile weight-loss and diabetes medications. Anvisa recorded five reports associated with Ozempic, three with Wegovy, two with Wegovy FlexTouch, and two with Rybelsus—all Novo Nordisk products utilizing the active ingredient semaglutide. One report was associated with Mounjaro, produced by Eli Lilly and containing tirzepatide.
This is not the first time the regulator has flagged the issue. In June 2025, Anvisa issued an official alert classifying NAION as a very rare adverse event associated with semaglutide. The agency subsequently mandated that manufacturers include warnings about this potential risk on product labels for medications containing the substance.
A ‘Small Heart Attack’ in the Eye
NAION occurs when blood flow to the anterior portion of the optic nerve is reduced. Gustavo Bonfadini, an ophthalmologist, specialist in cataract surgery and doctor in ophthalmology at the Federal University of São Paulo (Unifesp), describes the condition as a "small heart attack" in the optic nerve head.
The optic nerve functions as a cable carrying information from the retina to the brain. When blood flow drops, nerve fibers are deprived of oxygen and nutrients, leading to permanent vision loss. It is often painless. Bonfadini notes that patients frequently go to sleep with normal vision and wake up to find a missing section in their visual field, often affecting the upper or lower portions of their sight.
The Difficulty of Proving Causality
Anvisa has emphasized that these notifications do not confirm the medications caused the vision loss. Determining a direct link requires a comprehensive analysis of clinical data, including diagnostic confirmation, timing, and the patient’s underlying health.
The condition is multifactorial. Established risk factors include hypertension, diabetes, high cholesterol, cardiovascular disease, smoking, obstructive sleep apnea, and being over age 50. Clayton Macedo, a professor at Unifesp and communications director for the Brazilian Society of Endocrinology and Metabolism (SBEM), characterizes the association between GLP-1 agonists and NAION as extremely rare. While a signal of an association exists, Macedo says establishing a direct cause-and-effect relationship remains difficult.
Clinical Data and Industry Pushback
Novo Nordisk maintains that the safety profile of semaglutide is supported by global usage data and extensive clinical study programs. The company stated that patient safety remains its priority and that currently available evidence does not confirm a causal relationship between GLP-1 agonists and NAION.
The data presents a complex picture. Research published in Diabetes Care observed an incidence of 18 cases of NAION per 100,000 person-years among GLP-1 users, compared to 7.2 cases per 100,000 person-years among users of DPP-4 inhibitors. However, researchers cited in JAMA Ophthalmology note that diabetes patients—the primary target for these drugs—already face a higher baseline risk for vascular and ophthalmic issues.
Health authorities continue to recommend that patients seek immediate medical attention if they experience sudden loss or rapid deterioration of their vision while using these medications.
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