Novo Nordisk Sues Eli Lilly Over Weight-Loss Drug Ads, Saying the Dose Comparison Is Rigged

On July 21, 2026, Novo Nordisk announced it had sued Eli Lilly in federal court over Lilly's national television and online advertising for Zepbound and Mounjaro.

The case is Novo Nordisk Inc. v. Eli Lilly and Company et al., number 3:26-cv-09027, in the US District Court for the District of New Jersey. The complaint is dated July 20 and names both Eli Lilly and Company and Lilly USA, LLC.

The core allegation is about doses. Novo says Lilly's ads stack tirzepatide at its highest tolerated doses, 10 mg and 15 mg, against semaglutide at 1.7 mg and 2.4 mg, while saying nothing about the 7.2 mg dose of injectable Wegovy that the FDA approved in March 2026. That higher dose was supported by the STEP UP trial, a 72-week study in which participants lost an average of 18.8% of their body weight, roughly 47 pounds, compared with 3.9% on placebo. Novo's position is that presenting older comparative data as though it reflects the current treatment landscape misleads patients about what semaglutide can do.

The complaint brings claims under the Lanham Act, the federal false advertising law, along with state false advertising and unfair competition statutes. Novo asks the court to permanently stop the ads, order corrective advertising, and award damages. Novo has said it sent Lilly a cease-and-desist letter first and that Lilly neither pulled the campaigns nor issued a correction.

Lilly disputes the claims. The company said the gold standard for comparing medicines is a well-conducted head-to-head randomized trial, pointing to SURMOUNT-5, which remains the only such trial directly comparing tirzepatide and semaglutide for weight management. Lilly described its advertising as truthful, transparent, and grounded in the most direct scientific evidence available. SURMOUNT-5 was a 72-week open-label study of 751 adults with obesity and without type 2 diabetes, published in the New England Journal of Medicine in May 2025, in which tirzepatide produced 20.2% average weight loss versus 13.7% for semaglutide. It tested semaglutide at the maximum tolerated dose available at the time, which was 1.7 mg or 2.4 mg, since the 7.2 mg dose was not yet approved.

Fierce Pharma later reported that Novo told the court it intended to seek a preliminary injunction to halt the ads while the case proceeds, with a filing planned for August 17.

Drug advertisements can hide dose assumptions

This is a fight between two companies, but it lands in patients' living rooms, because these are consumer ads. The useful lesson is that a comparison in a drug commercial is a marketing choice, and dose is one of the easiest things to shade. When you see a percentage attached to a drug name in an ad, the questions worth asking are which dose, for how long, in whom, and compared with what.

If you are deciding between semaglutide and tirzepatide, or wondering whether to move to the higher 7.2 mg Wegovy dose, that decision belongs with your prescriber and depends on your response so far, your side effects, your other conditions, and what your insurance will actually cover. A lawsuit filed by one manufacturer against another is not evidence about which drug will work better for you.

The complaint remains unproven

A complaint is a set of allegations, not a ruling. No court has decided whether Lilly's ads are misleading, and filing a case proves nothing. It also does not mean Zepbound is less effective than advertised, or that Wegovy at 7.2 mg outperforms tirzepatide; nobody has run a head-to-head trial at those doses, and comparing results across separate trials with different participants and designs is unreliable. Neither drug's safety is at issue in this case. The trial figures cited above come from the studies named, not from the litigation, and none of this should prompt you to start, stop, or switch a medication.