The European Medicines Agency’s safety committee has concluded that the use of Novo Nordisk’s popular weight-loss drug Wegovy and its treatments for type 2 diabetes may cause rare occurrences of a potentially dangerous eye condition.

Called non-arteritic anterior ischemic optic neuropathy (NAION), the condition may affect up to 1 in 10,000 people taking semaglutide, the active ingredient in Wegovy and Novo’s diabetes drugs Ozempic and Rybelsus, the regulator said on Friday.

The EMA, which started its review in December, said the use of the drugs is linked to about twofold increase in the risk of developing the condition compared to people not taking the medicine.

NAION develops from insufficient blood flow to the optic nerve and causes sudden painless vision loss in one eye. It is the second most common cause of blindness due to optic nerve damage, after glaucoma.

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Studies have linked semaglutide to NAION in the past. But this is the first time a regulator has made the link.

Semaglutide belongs to a class of drugs known as GLP-1 receptor agonists, which work by helping control blood sugar levels and triggering a feeling of fullness.

A large study of nearly 350,000 diabetics published earlier this year had showed that the risk of developing NAION more than doubled after long-term use of semaglutide, compared to patients taking medicines from other classes.

The EMA said it has reviewed all available data on NAION with semaglutide, including data from non-clinical studies, clinical trials and post-marketing surveillance.

It has recommended the drugmaker to update prescribing information for medicines containing semaglutide to include NAION as a side effect with a frequency of “very rare.”

The U.S. Food and Drug Administration did not immediately respond to a Reuters request for comment.