Novo Nordisk A/S and Eli Lilly & Co. must add warning labels to their weight-loss and diabetes drugs about a potential rare side effect that could permanently damage patients’ vision.

The U.S. Food and Drug Administration will now require GLP-1 drugs including Novo’s Wegovy and Ozempic and Lilly’s Mounjaro, Zepbound and Foundayo to carry warnings that they may increase the risk of non-arteritic anterior ischemic optic neuropathy, or NAION. The rare condition can cause decreased vision and potentially permanent vision loss.

Concerns have risen about the side effect in recent years. In 2024, a Harvard University study linked Novo’s Ozempic to an increased risk of vision loss. Last year, four patients who developed the serious eye condition won compensation in Denmark, where the company is headquartered.

Novo will continue to review new research and monitor the safety of its medicines, said Liz Skrbkova, director of media and stakeholder relations, in a statement.…