Brazil's Council of Ophthalmology (CBO) issued guidance on Tuesday (29) for patients using the so-called weight-loss pens, the injected diabetes and obesity drugs semaglutide and tirzepatide sold as Ozempic, Wegovy and Mounjaro. The move follows the disclosure by Anvisa, Brazil's health regulator, that it is investigating 13 reports of suspected NAION, a rare condition that cuts blood flow to the optic nerve and can cause sudden vision loss.
What exists so far are suspicions, with no confirmed cases. According to the state news agency Agência Brasil, 12 of the reports involve semaglutide, found in Ozempic, Wegovy and the oral version Rybelsus, and one involves tirzepatide, used in Mounjaro. The magazine Veja Saúde detailed the records as five reports of Ozempic, three of Wegovy, two of Wegovy FlexTouch, two of Rybelsus and one of Mounjaro.
Anvisa itself stresses that a report does not prove causation. "The presence of the drug and the event in one notification does not definitively establish that the drug caused the neuropathy or the vision loss," the agency said in a statement. Confirmation, it said, depends on case-by-case clinical review, including the diagnosis and other possible causes.
What specialists say
Mauro Goldbaum, secretary-general of the CBO, said patients with visual complaints should see an ophthalmologist, while those without symptoms should discuss eye monitoring with the doctor who prescribed the pen. The debate over a possible link gained force in 2024, after a US medical center reported a rise in cases among users of these drugs, according to Folha de S.Paulo. Studies have since been conducted, but Goldbaum said they carry significant limitations: they are retrospective analyses of existing databases, without the rigor of a controlled trial, and the users' group already had a more complex clinical profile, with risk factors of their own for cardiovascular and eye disease.
"You take a database and compare the patients who used the pen with those who did not. We cannot control whether the two groups are truly equivalent. Intuitively, we imagine that the group that used the pen was probably already sicker, with diabetes and obesity, otherwise they would not have used it."
Plausible mechanisms exist, but they remain unconfirmed. Ophthalmologist Emilio Suzuki, president of the Brazilian Society of Ophthalmology, told Agência Brasil that rapid weight loss can cause low blood pressure and reduce blood flow, while diabetes and obesity on their own worsen circulation, including in the eye. Novo Nordisk, maker of semaglutide, said in a statement that clinical trials showed no increased incidence of this type of neuropathy. Eli Lilly, maker of Mounjaro, said it monitors safety information on its medicines, including eye-related issues.
What patients should do
In June 2025, Anvisa had already warned about sudden vision loss as a very rare adverse event associated with semaglutide and ordered the risk to be added to package inserts. The pens require a prescription and medical follow-up. Anyone who experiences sudden vision loss, blurred vision or rapidly worsening sight during treatment should seek medical care immediately, the agency said.