Pharmaceutical giant Novo Nordisk has officially filed a federal lawsuit against its main competitor Eli Lilly in the District Court of New Jersey, CNBC reported.
The lawsuit accuses the American company of misleading advertising and unfair competition in the multi-billion dollar market for weight loss drugs. According to the Danish manufacturer, Lilly's national advertising campaigns for its hit GLP-1 products violate the Lanham Act because they intentionally use outdated scientific data to suggest the categorical superiority of its drugs over Novo's.
The Dosing Dispute: Wegovy vs. Zepbound
The legal conflict is based on a large-scale television and digital campaign by Eli Lilly for the drug Zepbound (tirzepatide) and the diabetes drug Mounjaro. These ads, aired during major sporting events and on social media platforms TikTok and Facebook, claim that patients taking Zepbound lose an average of 50 pounds, while those on Wegovy (semaglutide) lose only 15 kg.
Novo Nordisk counters that this comparison is deeply manipulative, as Lilly compares the highest dose of its product with lower and outdated doses of Wegovy of 1.7 mg and 2.4 mg. The Danish company's general counsel, John Kukkelman, commented to Reuters, quoted by BTA, that the data no longer reflects reality. In March 2026, the US Food and Drug Administration (FDA) approved a new, higher dose of Wegovy of 7.2 mg.
Clinical trials show that at this dose, patients achieve an average weight loss of 21.3 kg, which is clinically identical to the results of Zepbound. The same discrepancy is seen in the Mounjaro ads, where the maximum dose of 15 mg is compared to the lowest available Ozempic dose of 1 mg.
The scale of the damage and escalation today
Eli Lilly's ads generated over 700 million impressions since the end of April, causing serious market damage to Novo Nordisk. The Danish company has already sent an official warning letter, but the American competitor has only responded by adding “illegible and microscopic text below the line“, which does not change the overall message of the advertisement.
On July 24, the conflict reached its peak after Novo Nordisk filed a request for an immediate injunction, demanding that the court immediately stop the broadcast of the clips. The plaintiffs are demanding that Lilly be forced to conduct a large-scale “corrective advertising campaign“ and to pay financial damages equal to the profits generated by those ads.
Eli Lilly's counterattack
For its part, the American corporation categorically rejected the accusations. In an official statement, a spokesperson for Eli Lilly announced that the company stands firmly behind its marketing messages. According to them, the campaign is based on the study Surmount-5, which is currently the only head-to-head, randomized clinical trial comparing tirzepatide and semaglutide. Lilly emphasizes that its advertising is transparent, based on scientifically proven facts, and accuses Novo Nordisk of trying to hide the real results from the market through legal means, instead of competing with the qualities of its products.
Wall Street analysts note that this aggressive legal offensive reflects a change in Novo Nordisk's strategy. After Wegovy's market share in the US was seriously threatened by the explosive growth of Zepbound in the last year, the Danish leader is determined to regain its position. The battle for the weight loss drug market, which is expected to exceed $100 billion by 2030, has now officially moved from the labs right into the courtroom.