People who take a massively popular diabetes and weight loss drug may have an increased chance of developing a rare vision condition that could lead to blindness, according to a new study. Researchers at Mass Eye and Ear—a Harvard-affiliated teaching hospital in Boston, found that patients taking semaglutide—marketed as Ozempic and Wegovy—have a higher likelihood of developing nonarteritic anterior ischemic optic neuropathy (NAION).

The stock of the company behind Ozempic, Novo Nordisk, dipped sharply following the release of the report.

Patients with diabetes who were prescribed semaglutide were approximately four times more likely to be diagnosed with NAION compared to those not taking the medication, the study found. The risk was even higher for overweight or obese patients, who were over seven times more likely to develop the condition.

NAION is a rare condition, affecting only 2-10 people per 100,000. It involves potentially dangerous reductions in blood flow to the optic nerve, which can lead to permanent vision loss in the eye.

"The use of these drugs has exploded throughout industrialized countries and they have provided very significant benefits in many ways, but future discussions between a patient and their physician should include NAION as a potential risk," said Joseph Rizzo, the study's corresponding author and director at Mass Eye and Ear, according to a statement shared by CNN.

For its part, Novo Nordisk told the National Post that it remains confident in Ozempic’s safety—even though it takes negative reports “very seriously.”

“Semaglutide has been studied in large real-world evidence studies and robust clinical development programs with a cumulative exposure including from post-marketing use of over 22 million patient years,” the company said. “The totality of data provides reassurance of the safety profile of semaglutide.”

The company did not immediately respond to a request for comment from Decrypt.

Novo Nordisk's stock (NVO) fell nearly 5% Wednesday to $136 before recovering slightly to close at $138.60. The news also appeared to impact drugmaker Eli Lilly (LLY), which produces similar diabetes and weight-loss drugs Mounjaro and Zepbound, with its stock dipping close to 3% to end at $898.10.

Ozempic, first approved by the FDA in December 2017 for type 2 diabetes treatment, quickly achieved blockbuster status with over $1 billion in global sales within its first two years on the market.

The drug works by mimicking the hormone GLP-1, which helps regulate appetite and blood sugar levels. This mechanism makes patients feel fuller and less hungry, leading to reduced calorie intake and subsequent weight loss. In clinical studies, people with obesity who took Ozempic in combination with lifestyle changes lost more weight than those not taking the medication.

Ozempic is primarily indicated for improving blood sugar levels in adults with type 2 diabetes and reducing the risk of major cardiovascular events in those with established heart disease, but many healthcare providers have been prescribing it for weight loss due to its effectiveness.

The researchers noted that the highest risk of developing NAION was observed within the first year of starting semaglutide treatment. However, they emphasized that the study does not conclusively prove that Ozempic or Wegovy directly cause NAION, and further research is needed to establish a causal relationship.

In response to the study, some experts recommend caution.

“I don’t think this is a strong enough signal to take patients off the drug,” Susan Mollan, a neuro-ophthalmologist in Birmingham, England, told Bloomberg.

The study's results come at a time when Ozempic and similar drugs have been hailed as game-changers in the treatment of diabetes and obesity. Their popularity has soared to the point that markets have been struggling to keep up with the demand, creating a very lucrative market for drugmakers.

In a previous controversy, a study from March 2024 concluded that Ozempic could be profitably produced for less than $5 a month, a stark contrast to its current US list price of $915. Still, demand for the drug has not subsided, nor has the price decreased. Novo Nordisk stock fell over 12% after the release of the cost study, but soon rebounded.

Another popular drug, Viagra, has also been linked to vision problems, and is still extremely popular.

Edited by Ryan Ozawa.