Brazil's national health surveillance agency Anvisa has launched an investigation into 13 cases of a rare optic nerve disorder causing vision loss in patients using popular GLP-1 diabetes and weight-loss medications.
The Brazilian regulatory body confirmed on Monday, September 28, 2026, that the reports involve five cases linked to Ozempic, three to Wegovy, two to Wegovy FlexTouch, one to Mounjaro, and two to Rybelsus, an oral form of semaglutide.
Of the 13 total notifications under review, 12 involve treatments formulated with semaglutide and one is associated with tirzepatide.
Anvisa emphasized that all notifications remain under active investigation and do not establish a definitive causal link between the medications and the onset of neuropathy or vision loss.
Understanding the eye condition
The condition under investigation is non-arteritic anterior ischemic optic neuropathy, also known as NAION or NOIANA. It is a rare eye disorder that impairs the optic nerve, the essential structure that transmits visual impulses from the eye to the brain, potentially resulting in partial or total loss of sight.
The disease typically manifests as a sudden and painless loss of vision, usually affecting only one eye.
Dr. Alléxya Affonso, an ophthalmologist specializing in clinical retina, uveitis, and ocular oncology, said it is crucial to differentiate a potential risk from the misconception that every patient taking these medications will develop vision problems.
Affonso, who holds a doctorate in ophthalmology and visual sciences from the Federal University of São Paulo, explained that NAION occurs when blood flow to the optic nerve is reduced. When ischemia strikes this region, significant vision loss can occur.
She noted that patients with type 2 diabetes, high blood pressure, obesity, cardiovascular changes, and other metabolic factors may already present a higher risk of vascular changes related to the disease.
Affonso emphasized that the message should not be one of panic or stopping medication without professional advice. She advised that because NAION is a rare condition, the most important step for patients is to recognize warning signs and seek immediate medical care if they notice a sudden change in vision.
GLP-1 receptor agonists like semaglutide and tirzepatide work by mimicking natural metabolic hormones to regulate blood sugar levels and suppress appetite, making them widely prescribed for both type 2 diabetes management and clinical weight management.
Previous health alerts and sales rules
The latest investigation follows earlier regulatory action by Brazilian health authorities. In June 2025, Anvisa issued a formal alert regarding cases of sudden vision loss associated with the use of medications containing semaglutide, such as Ozempic, Rybelsus, and Wegovy.
At that time, the agency mandated that drug manufacturers include NAION in the package leaflets of these medications as a very rare adverse reaction.
Prior to that decision, health officials had recorded approximately 52 notifications of suspected eye disorders related to semaglutide use across the country.
In the same month, Anvisa instituted stricter sales controls for all GLP-1 receptor agonist medications, requiring pharmacies to retain physical medical prescriptions upon dispensing them.
As Brazil's central regulatory authority based in Brasília, Anvisa monitors pharmaceutical safety standards across South America's largest healthcare market.
Drug manufacturers respond to reports
Danish pharmaceutical company Novo Nordisk, the manufacturer of Wegovy, Ozempic, and Rybelsus, said patient safety is its top priority and stressed that semaglutide maintains a well-established safety profile. The company recommended that patients obtain accurate diagnosis and treatment while remaining under medical supervision throughout their care.
In an official statement, Novo Nordisk said NAION is being evaluated as part of its routine pharmacovigilance. The company stated that continuous monitoring of all safety data has not altered that conclusion and that a causal relationship between GLP-1 receptor agonists, including semaglutide, and NAION cannot be confirmed based on the totality of available data.
The manufacturer explained that its assessment is based on the absence of numerical imbalances in clinical trial data, limitations in the few available epidemiological studies, an absence of evidence in non-clinical data, inconsistent patterns among post-marketing cases, and the lack of any known biological mechanism of action.
Novo Nordisk added that it found no warning signals in clinical trials involving semaglutide. Considering all available clinical, observational, and post-marketing evidence alongside the low overall incidence of NAION, the company stated that the benefit-risk profile of semaglutide remains favorable, adding that appropriate measures will be implemented if emerging data requires action.
Lilly do Brasil, representing American drugmaker Eli Lilly which produces Mounjaro, stated that patient safety is its primary priority. The company said it actively monitors, evaluates, and reports safety information to regulatory authorities for all of its pharmaceutical products.
Lilly do Brasil noted that as part of its routine safety review process, it maintains ongoing discussions with regulatory authorities regarding potential safety topics, including ophthalmological issues. The company advised anyone experiencing side effects while using its medications to speak with their doctor or healthcare professional.
