Ongoing lawsuits allege GLP-1s can cause serious harm. But we don't know how often

Todd Engel had operated heavy machinery, like forklifts and rubber-tire loaders, around warehouses and highways in suburban Maryland for four decades. In early 2023, Engel's doctor put him on Ozempic, a GLP-1, for diabetes. That winter, on New Year's Eve, Engel woke up feeling as if a patch covered his right eye: "I couldn't see anything.

It was black." The doctor told Engel and his wife Shelley it was a form of optic neuropathy — NAION, for short – an inoperable condition caused by tiny strokes that cut off blood flow to his eye. When the doctor listed all known causes, Shelley Engel specifically asked about Ozempic. "'We have heard nothing about that,'" she recalls the doctor telling her.

Seven months later, the journal JAMA Ophthalmology did publish research showing higher rates of NAION among diabetic patients taking Ozempic, or semaglutide, as the active ingredient name is known. But neither Engel nor his doctor were aware, so Engel kept taking weekly shots until his left eye went black, just as the other had done the year prior. More than one in 10 Americans are taking a GLP-1 drug for weight loss, according to a recent Gallup analysis, and one in seven has taken them at some point.

The drugs are prescribed for a growing number of conditions and come with a range of side effects. Engel has filed a lawsuit alleging the maker of Ozempic, Novo Nordisk, failed to warn patients and doctors about the risk of NAION. His suit is part of two main ongoing consolidated lawsuits alleging life-threatening or life-altering harm from GLP-1 drugs.

In a statement to NPR, spokespeople for Novo Nordisk pointed to subsequent research casting doubt on whether their GLP-1 drug causes NAION, for example, and said the cases are without merit. Want the latest stories on the science of healthy living? Subscribe to NPR's Health newsletter.

The legal question before the courts hinges in part on whether the GLP-1 drugs caused the harm. Observational data can show correlation — that people taking GLP-1s were perhaps more likely to have this eye complication occur — but not causation. For that, more detailed investigation is needed.