Eli Lilly reported Thursday that in a late-stage trial, its next-generation obesity drug led to levels of weight loss approaching the effectiveness seen with bariatric surgery, but that there were high rates of side effects and discontinuations, raising questions about how appealing the treatment would be. 

In the Phase 3 study, which enrolled obese and overweight people who didn’t have diabetes, those who took the highest dose and stayed on the treatment, called retatrutide, lost on average 28.3% of their weight after 80 weeks.

But 11% of patients on the highest dose discontinued due to adverse events, and when analyzing all participants, including those who discontinued, the efficacy was 25%. (In pivotal trials of drugs on the market — Novo Nordisk’s Wegovy and Lilly’s Zepbound — discontinuation rates due to side effects were up to 7%.)

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