The weight-loss jab Wegovy may carry the highest risk of sudden sight loss compared to other semaglutide drugs such as Ozempic, according to new analysis.
The odds of having a so-called "eye stroke" were also three times higher in men than women, the study suggested.
Researchers said the findings, published in the British Journal of Ophthalmology, "highlight a potential dose-dependent safety concern" for semaglutide.
Semaglutide brands Wegovy, Ozempic and Rybelsus - made by Novo Nordisk - all have the same active ingredient, but differ in dosage and use.
Wegovy is approved on the UK's National Health Service to help people lose weight in higher doses.
Ozempic uses lower doses to treat type 2 diabetes, along with Rybelsus, which is a pill rather than a jab.
For the study, experts examined the link between semaglutide and ischaemic optic neuropathy (Ion) - often called an eye stroke - which causes a sudden loss of vision due to reduced blood flow to the optic nerve.
Researchers analysed side-effect alerts submitted to the US Food and Drug Administration (FDA) Adverse Event Reporting System between December 2017 and December 2024.
Of more than 30 million alerts, some 31,774 involved semaglutide.
Some 3,070 were attributed to Wegovy, which launched in 2021, while 20,608 were linked to Ozempic, which was approved by the FDA in 2017.
Despite this, researchers found Wegovy was most strongly linked with Ion compared to Ozempic.
"Overall, Ion risk appears dose and formulation dependent, and highest with Wegovy," they said.
"Ozempic's earlier approval resulted in more reports than Wegovy, yet Wegovy showed the stronger signal."
Further analysis suggested the odds of Ion were almost five times higher with Wegovy than Ozempic, and more than three times higher in men than in women.
Researchers said: "These findings highlight a potential dose-dependent safety concern that warrants urgent prospective evaluation to guide prescribing and regulatory policy."
Meanwhile, Ion was not reported in association with Rybelsus, the study found.
Experts said this difference may be down to "the limited absorption and slower uptake of Rybelsus".
A Novo Nordisk spokesperson said: "Patient safety is our top priority, and we take any reports about adverse events from the use of our medicines very seriously.
"We work closely with authorities and regulatory bodies from around the world to continuously monitor the safety profile of our products."
They added that EU patient leaflets for Wegovy, Ozempic and Rybelsus have been updated to include non-arteritic anterior ischemic optic neuropathy (NAION).
However, the company has concluded that data "did not suggest a reasonable possibility of a causal relationship between semaglutide and NAION and Novo Nordisk believes that the benefit-risk profile of semaglutide remains favourable".
