Brazil's health regulatory agency Anvisa announced Tuesday new safety measures for GLP-1 receptor agonist drugs, including semaglutide and tirzepatide, after its investigation into reports of sudden vision loss expanded beyond the 13 cases disclosed last week. The agency ordered manufacturers to add warnings about the eye condition NAION to product labels.

The move followed Anvisa's disclosure on September 27 that it had opened a formal investigation into notifications linking the popular diabetes and weight-loss medications to non-arteritic anterior ischaemic optic neuropathy, a disorder that can cause permanent loss of sight. The drugs are marketed in Brazil under brand names including Ozempic, Wegovy and Mounjaro.

Anvisa required Novo Nordisk and Eli Lilly to update patient information leaflets and strengthen pharmacovigilance reporting for suspected ocular events. The agency advised patients experiencing sudden vision changes to seek immediate medical attention and consult their prescribing physicians.

The decision aligns Brazil with regulators elsewhere who have examined the same signal. The European Medicines Agency's safety committee concluded in 2025 that NAION was a very rare side effect of semaglutide, and the medicine's European labelling was amended accordingly. Anvisa's action extends similar scrutiny to tirzepatide amid soaring prescription volumes across Latin America.

GLP-1 drugs have become among the best-selling medicines worldwide, driven by demand for weight management. Novo Nordisk has maintained that the overall benefit-risk balance of its products remains positive and that ocular events are extremely rare.