Novo Nordisk sued Eli Lilly in federal court on Tuesday over weight-loss drug advertising, and the whole complaint turns on a single question: which doses you put next to each other.
The suit, filed in U.S. District Court in New Jersey and reported by the Guardian ↗, accuses Lilly of a pattern of "false and materially misleading" ads that compare its own drugs against Novo's. Both companies make two versions of the same molecule. Novo sells semaglutide as Wegovy for weight loss and Ozempic for diabetes; Lilly sells tirzepatide as Zepbound and Mounjaro. Novo says the campaign misled millions of Americans living with obesity and type 2 diabetes and broke federal and state false-advertising and unfair-competition laws. Novo's general counsel put the charge plainly, saying Lilly is "intentionally confusing consumers."
The dose sleight of hand
Here is the specific complaint. Novo says Lilly's ads stack the highest approved dose of tirzepatide ↗ against an older, lower dose of semaglutide ↗, and leave out the fact that the FDA approved a stronger 7.2 mg version of Wegovy in March 2026. Novo's suit cites a trial of that higher dose in which patients lost about 47 pounds on average, and one in three lost roughly 62 pounds. Compare a drug's ceiling against a competitor's older, lower rung and you can make almost any winner you like.
This is why dose is not a footnote for these drugs. Both semaglutide and tirzepatide are titrated slowly upward over months, and how much weight a patient loses depends heavily on where that titration stops. A comparison that fixes one drug at its maximum and the other below its own new maximum is not comparing the drugs. It is comparing two dosing choices.
Lilly's defense is also about dose
Lilly says it stands by its advertising, which leans on a genuine 2024 head-to-head trial that tirzepatide won. That trial was real, and at the doses it tested tirzepatide did come out ahead. The catch is that it ran before Novo's 7.2 mg Wegovy existed, so it compared tirzepatide's top dose against semaglutide's old top dose. Novo's own filing concedes the gap it is exploiting: there is, it says, no head-to-head trial comparing the highest approved doses of the two medicines. Neither side can currently point to that trial because nobody has run it.
Novo is asking the court for a permanent injunction that would pull Lilly's comparative ads and force a corrective campaign. Whether the ads are false or merely outdated is now a question for a judge, and the honest answer is that the strongest claim either company can make about being the better drug rests on a comparison that does not yet exist. We wrote about a related gap when tirzepatide matched semaglutide on mental health ↗ while both beat the older GLP-1 shots. The weight-loss race between them is being fought in ad copy and court filings precisely because the trial that would settle it has not been done.