On Weight-Loss Drugs? Watch Your Vision

Millions of people worldwide, including in India, using popular diabetes and weight-loss medicines may need to pay closer attention to their eye health after the US Food and Drug Administration (FDA) flagged a potential risk of a rare condition that can cause sudden vision loss.

In a safety communication issued on November 9, the US regulator said medicines belonging to the glucagon-like peptide-1 (GLP-1) class may be associated with non-arteritic anterior ischaemic optic neuropathy (NAION), a condition caused by reduced blood supply to the optic nerve. It can lead to sudden, painless loss of vision in one eye and, in some cases, permanent visual impairment.

The FDA has asked manufacturers of GLP-1 medicines to include information about this potential risk in the 'Warnings and Precautions' section of their product labels. The medicines covered include semaglutide, marketed as Ozempic, Wegovy and Rybelsus; liraglutide; dulaglutide; and tirzepatide, sold under the brand names Mounjaro and Zepbound. Tirzepatide acts on both GIP and GLP-1 receptors.

The warning assumes significance in India, where these medicines are gaining popularity for diabetes management and weight loss. The International Diabetes Federation estimates that nearly 90 million adults in India were living with diabetes in 2024. The expanding use of GLP-1 medicines has also raised concerns about inappropriate prescriptions and unsupervised consumption, particularly among people seeking rapid weight loss.

The FDA based its assessment on data from 126 randomised clinical trials involving 1,34,253 participants. It identified 15 probable cases of NAION — 10 among people taking GLP-1 medicines and five in comparison groups.

NAION occurs when blood flow to the optic nerve is reduced, damaging the nerve fibres responsible for transmitting visual information to the brain. Symptoms can include sudden, painless vision loss in one eye, blurred vision, blind spots and changes in colour perception. Any sudden change in vision requires urgent medical assessment.

The estimated incidence was 6.4 cases per 1 lakh person-years among GLP-1 users, compared with 3.8 among those receiving a placebo or other glucose-lowering medicines.

The agency also reviewed real-world data and published observational studies. While some studies suggested an increased risk compared with certain other diabetes medicines, the available evidence does not establish that GLP-1 drugs directly cause NAION. The FDA has described the risk as potential and rare.

The warning adds to the existing concerns surrounding GLP-1 medicines, which, despite their benefits in controlling blood glucose and reducing body weight, can cause side effects. Nausea, vomiting, diarrhoea, constipation and abdominal discomfort are among the commonly reported problems. More serious concerns include gallbladder complications and pancreatitis. Persistent vomiting and diarrhoea can also lead to dehydration and, in some cases, kidney complications.

Doctors have also cautioned against rapid weight reduction without adequate nutritional support. Patients can lose lean muscle along with body fat, making sufficient protein intake and physical activity important during treatment.

Studies have also shown that some patients regain weight after stopping these medicines, underlining the need for long-term obesity management rather than viewing the drugs as a short-term weight-loss solution.

India's drug regulator, the Central Drugs Standard Control Organisation (CDSCO), has already stepped up scrutiny of the GLP-1 market. In March 2026, it issued an advisory to manufacturers against surrogate advertisements and indirect promotion that could encourage inappropriate use of these prescription medicines. The regulator also conducted inspections and audits of 49 entities, including online pharmacy warehouses, wholesalers, retailers and slimming clinics, to check unauthorised sales and promotional practices.

The latest FDA communication adds another dimension to patient counselling. Doctors may need to discuss the potential eye-related risk with patients while assessing their medical history and other risk factors, including diabetes and hypertension, which are themselves associated with vascular complications.

However, patients should not discontinue their medicines on their own after reading the warning. Those experiencing sudden vision loss, blurred vision or other new visual disturbances should seek immediate ophthalmological care and contact the doctor prescribing the medicine to discuss further treatment.