Weight-loss drug receives FDA warning for rare eye disease; Novo Nordisk (NVO.US) and Eli Lilly (LLY.US): No evidence of causality

According to Zhitong Finance APP, the U.S. Food and Drug Administration (FDA) stated on Monday that after finding evidence of an increased risk of a rare eye disease, it will require all GLP-1 class drugs to include a new safety warning.

This disease, called non-arteritic anterior ischemic optic neuropathy (NAION), can cause sudden vision loss. It is relatively rare, and a causal relationship has not yet been established.

The FDA stated that it will require all GLP-1 drug manufacturers to add a warning about the potential increased risk of NAION when using these drugs.

NAION is a condition that can lead to sudden vision decline, including permanent vision loss. The underlying cause is decreased blood flow to the anterior part of the optic nerve, but the root cause remains unclear.

The FDA noted that there have been reports of NAION cases for all GLP-1 products currently on the market.

Ozempic and Wegovy manufacturer Novo Nordisk (NVO.US) said the company "still believes the data do not establish a causal relationship and continues to be confident in the benefit-risk profile of its GLP-1 medicines."

Mounjaro, Zepbound, and Foundayo manufacturer Eli Lilly (LLY.US) stated that it is "carefully evaluating this update and will respond to the FDA as soon as possible." The pharmaceutical company added that patient safety is Eli Lilly's "top priority."

Diabetes itself is a known risk factor for NAION, which makes it complicated to determine whether cases among GLP-1 users are caused by the drug or by the underlying condition.

The FDA made this decision after reviewing clinical trials, real-world patient data, and published studies.

An analysis covering 126 trials and over 134,000 patients found that the incidence of NAION among GLP-1 users was 6.4 cases per 100,000 patient-years, compared to 3.8 for those on other treatments or placebo.

The FDA said it had identified 15 suspected cases of NAION, 10 occurred in patients treated with GLP-1s, 5 in those receiving placebo, and none among patients on other non-GLP-1 glucose-lowering drugs.

Several observational studies have also found an increased risk, supporting the FDA's concerns.

When comparing the risk of NAION with GLP-1 drugs to that of other commonly used diabetes medications, the FDA's findings were more mixed.

According to the FDA, real-world patient data showed a statistically significant increase in the risk of NAION among GLP-1 users compared to patients on another diabetes drug class, DPP-4 inhibitors; but not when compared to patients on SGLT-2 inhibitors. SGLT-2 inhibitors are another drug class, including Jardiance and Farxiga.

However, the FDA added that observational studies consistently report that among patients with type 2 diabetes, those initiating GLP-1 therapy have an increased risk of NAION compared with those starting on DPP-4 inhibitors or SGLT-2 inhibitors.

Citi analysts believe that the FDA's class-wide labeling action "may cause concern but should have a limited effect on GLP-1 adoption."

They added that the move may temporarily increase anxiety among patients and investors, but given the rarity of NAION and the significant benefits GLP-1 drugs offer for weight loss, blood sugar control, cardiovascular, kidney, and sleep apnea outcomes, the benefit-risk profile should remain favorable and prescription changes will be modest.

Benefits and Risks

Although GLP-1 drugs have been shown to offer benefits beyond weight loss and blood sugar control, many of these drugs also carry the FDA’s strongest safety warning—a “black box warning” about the potential risk of thyroid tumors.

Research shows that the active ingredient in Wegovy and Ozempic, semaglutide, and the active ingredient in Mounjaro, tirzepatide, cause thyroid C-cell tumors in rodents. It is not yet clear whether these drugs cause such tumors, including a rare form of thyroid cancer, in humans.

Semaglutide and tirzepatide also carry warnings about diabetic retinopathy—another eye disease that can cause blurred vision, difficulty seeing in dim light, and eventually vision loss. Diabetic retinopathy refers to damage to the small blood vessels in the retina (the light-sensitive tissue at the back of the eye) caused by high blood sugar.

According to Ozempic’s prescribing information, in a two-year trial involving patients with type 2 diabetes at high cardiovascular risk, 3% of patients treated with Ozempic experienced diabetic retinopathy complications, compared to 1.8% in the placebo group.

Mounjaro’s FDA label also warns that rapid improvement in glycemic control is associated with temporary worsening of diabetic retinopathy and recommends monitoring patients with a history of this condition.

FDA Decision Follows European Warning

European regulators warned about the NAION risk associated with semaglutide as early as June 2025.

The European Medicines Agency’s (EMA) safety committee determined that NAION is an extremely rare side effect of semaglutide, potentially affecting up to 1 in every 10,000 patients. They recommended updating the product information for the drug. The UK medicines regulator issued a similar warning in February this year.

Unlike the FDA’s latest action, which covers all GLP-1 drugs, the European and UK warnings apply only to semaglutide.