Weight-loss wonder drugs get FDA warning label for "rare eye disease"; Novo Nordisk A/S Sponsored ADR Class B (NVO.US) and Eli Lilly (LLY.US): no evidence of causation

The U.S. Food and Drug Administration (FDA) said on Monday it will require a new safety warning on all GLP-1 drugs after finding evidence of a potential increased risk of a rare eye condition. The condition, called non-arteritic anterior ischemic optic neuropathy (NAION), can cause sudden vision loss, is rare, and a causal link has not been established. The FDA said it will require all manufacturers of GLP-1 drugs to add a warning about the potential increased risk of NAION associated with use of these drugs. NAION is a condition that can cause sudden vision loss (including permanent vision loss) due to reduced blood flow to the front of the optic nervebut its underlying cause is not fully understood. The FDA said NAION cases have been reported for all GLP-1 products currently on the market. Novo Nordisk A/S Sponsored ADR Class B (NVO.US), the maker of Ozempic and Wegovy, said the company "continues to believe the data do not establish a causal relationship and remains confident in the benefit-risk profile of its GLP-1 drugs." Eli Lilly (LLY.US), the maker of Mounjaro, Zepbound and Foundayo, said it is "carefully evaluating this update and will respond to the FDA as soon as possible." The drugmaker added that patient safety is Lilly's "top priority." Diabetes itself is a known risk factor for NAION, which complicates determining whether cases among GLP-1 users are caused by the drug or by patients' underlying disease. The FDA's decision came after reviewing clinical trials, real-world patient data and published studies. An analysis covering 126 trials and more than 134,000 patients found the incidence of NAION among GLP-1 users was 6.4 cases per 100,000 patient-years, compared with 3.8 cases among patients receiving other treatments or placebo. The FDA said it identified 15 suspected NAION events, of which 10 occurred in patients receiving GLP-1 treatment and 5 in patients receiving placebo, with no cases found among patients receiving other non-GLP-1 glucose-lowering drugs. Multiple observational studies also found an increased risk, supporting the FDA's concerns. When comparing the risk of NAION between GLP-1 drugs and other commonly used diabetes drugs, the FDA's findings were more mixed. According to the FDA, real-world patient data found a statistically significant increase in NAION risk among GLP-1 users compared with patients taking another class of diabetes drugs, DPP-4 inhibitors; but no such increase compared with patients taking SGLT-2 inhibitors, another drug class that includes Jardiance and Farxiga. However, the FDA added that observational studies consistently reported an increased risk of NAION among patients with type 2 diabetes who initiated GLP-1 treatment compared with those who initiated DPP-4 inhibitors or SGLT-2 inhibitors. Citi analysts believe the FDA's class-wide labeling action "may generate attention, but the impact on GLP-1 adoption should be limited." They added that the move could temporarily heighten concerns among patients and investors, but given the rarity of NAION and the significant benefits of GLP-1 drugs in weight loss, blood sugar, cardiovascular, kidney and sleep apnea, their benefit-risk profile should remain favorable, and changes in prescribing will be limited. Benefits and risks Although GLP-1 drugs have been shown to provide benefits beyond weight loss and blood sugar control, many of these drugs also carry the FDA's most severe safety warninga "boxed warning" about the potential risk of thyroid tumors. Studies show that semaglutide, the active ingredient in Wegovy and Ozempic, and tirzepatide, the active ingredient in Mounjaro, cause thyroid C-cell tumors in rodents. It is not known whether these drugs cause such tumors in humans, including a rare type of thyroid cancer. Semaglutide and tirzepatide also carry warnings about diabetic retinopathyanother eye condition that can cause blurred vision, difficulty seeing in low light and eventually vision loss. Diabetic retinopathy is a disease in which high blood sugar damages tiny blood vessels in the retina (the light-sensitive tissue at the back of the eye). According to the Ozempic prescribing information, in a two-year trial involving patients with type 2 diabetes and high cardiovascular risk, 3% of patients treated with Ozempic experienced diabetic retinopathy complications, compared with 1.8% in the placebo group. The FDA label for Mounjaro also warns that rapid improvement in blood sugar control is associated with a temporary worsening of diabetic retinopathy, and recommends monitoring patients with a history of the condition. FDA decision follows European warnings European regulators flagged the NAION risk associated with semaglutide as early as June 2025. The European Medicines Agency's (EMA) safety committee determined that NAION is a very rare side effect of semaglutide, potentially affecting up to 1 in 10,000 people taking the drug, and recommended updating the product information. The UK medicines regulator followed with 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.