Weight loss magic drug warned by FDA for “rare eye disease”. Novo Nordisk (NVO.US) and LLY.US (LLY.US): There is no evidence to prove cause and effect
The Zhitong Finance App learned that the US Food and Drug Administration (FDA) said on Monday that it will require all GLP-1 drugs to be given a new safety warning after finding evidence of an increased potential risk of a rare eye disease.
This disease, called nonarteritic anterior ischemic optic neuropathy (NAION), can cause sudden vision loss. It is rare, and no causal relationship has been established.
The FDA said it will require all manufacturers of GLP-1 drugs to be warned about the increased risk of NAION that may be caused by the use of such drugs.
NAION is a condition that can cause sudden vision loss (including permanent vision loss) due to decreased blood flow to the anterior part of the optic nerve — but the underlying cause is not fully understood.
According to the FDA, all GLP-1 products currently on the market have NAION case reports.
Ozempic and Wegovy's producer Novo Nordisk (NVO.US) said the company “still believes that the data cannot establish a causal relationship, and continues to be confident about the benefit-risk profile of its GLP-1 drug.”
LLY.US (LLY.US), the producer of Mounjaro, Zepbound, and Foundayo, said it is “carefully evaluating this update and will respond to the FDA as soon as possible.” The pharmaceutical company added that patient safety is Lilly's “number one priority.”
Diabetes itself is a known risk factor for NAION, making it complicated to determine whether cases among GLP-1 users are caused by drugs or the patient's underlying disease.
The FDA's decision came after reviewing clinical trials, real-world patient data, and published studies.
An analysis of more than 134,000 patients covering 126 trials found that the incidence of NAION among GLP-1 users was 6.4 cases per 100,000 patients per year, compared to 3.8 cases in patients receiving other treatments or placebos.
The FDA said it identified 15 suspected NAION events, 10 of which occurred in patients receiving GLP-1 treatment, 5 in patients receiving placebo, and no cases were found in patients receiving other non-GLP-1 hypoglycemic agents.
A number of observational studies have also found increased risk, supporting the FDA's concerns.
When comparing the risk of developing NAION from GLP-1 drugs with other commonly used diabetes medications, the FDA's findings are more mixed.
According to the FDA, real-world patient data found that GLP-1 users had a statistically significant increase in NAION risk compared to patients taking DPP-4 inhibitors, another type of diabetes drug; however, there was no such increase compared to patients taking SGLT-2 inhibitors. SGLT-2 inhibitors are another class of drugs, including Jardiance and Farxiga.
However, the FDA added that observational studies have consistently reported an increased risk of NAION in patients with type 2 diabetes compared to those who initially used a DPP-4 inhibitor or SGLT-2 inhibitor.
Citigroup analysts believe that the FDA's labeling action covering the entire drug category “may cause concern, but the impact on GLP-1 adoption should be limited.”
They added that the move may temporarily heighten patients' and investors' concerns, but given the rarity of NAION and the significant benefits of GLP-1 in weight loss, blood sugar, cardiovascular, renal and sleep apnea, the benefit-risk profile should remain favorable, and changes in prescriptions will be limited.
Benefits and risks
Although GLP-1 drugs have been shown to provide additional benefits beyond weight loss and blood sugar control, many of these drugs also carry the FDA's harshest safety warning — a “black box warning” about the potential risk of thyroid tumors.
Studies have shown that semaglutide (semaglutide), the active ingredient in Wegovy and Ozempic, and tirzepatide (tirzepatide), the active ingredient in Mounjaro, can cause thyroid C-cell tumors in rodents. It's unclear whether these drugs cause such tumors in humans, including a rare form of thyroid cancer.
Simeglutide and tirpotide also have warnings about diabetic retinopathy — another type of eye disease that can cause blurred vision, difficulty seeing in low light, and ultimately vision loss. Diabetic retinopathy is a disease in which high blood sugar damages the microblood vessels in the retina (the light-sensitive tissue at the back of the eye).
According to Ozempic prescription information, in a two-year trial involving patients with type 2 diabetes and high cardiovascular risk, 3% of patients treated with Ozempic developed diabetic retinopathy complications, compared to 1.8% in the placebo group.
Mounjaro's FDA label also warns that rapid improvements in blood sugar control are associated with temporary worsening of diabetic retinopathy, and recommends monitoring patients with a history of this condition.
FDA decision follows European alert
European regulators indicated NAION risks associated with simeglutide as early as June 2025.
The European Medicines Agency (EMA) safety committee determined that NAION is an extremely rare side effect of simeglutide, or affects up to 1 in every 10,000 people taking the drug, and recommended updating the product information for the drug. The UK Medicines Supervisory Authority followed up and issued a similar warning in February of this year.
Unlike the FDA's latest action to cover all GLP-1 drugs, the European and British warnings only target simeglutide.