LONDON, U.K.: Novo Nordisk has sued rival Eli Lilly in a U.S. federal court, accusing the drugmaker of misleading consumers by claiming its weight-loss medicines outperform Novo's treatments through advertising based on outdated comparisons.

The Danish pharmaceutical company filed the lawsuit on July 21 in U.S. District Court in New Jersey, alleging Lilly violated federal and state false advertising and unfair competition laws, including the Lanham Act, through nationwide advertising campaigns for obesity drug Zepbound and diabetes treatment Mounjaro.

Novo alleges Lilly compared the highest approved doses of its medicines with lower doses of Novo's Wegovy and Ozempic while omitting newer, higher-dose versions that Novo says deliver greater weight loss.

"The ads are maliciously and deceptively false because Lilly knowingly cites outdated clinical trials that compare the highest doses of the Lilly medicines to lower doses of Novo Nordisk's medicines," Novo wrote in its complaint.

Indianapolis-based Eli Lilly rejected the allegations, saying its advertising is based on results from its SURMOUNT-5 trial, completed in 2024. The study compared patients taking 10 mg or 15 mg doses of Zepbound with patients receiving 1.7 mg or 2.4 mg doses of Wegovy. The U.S. Food and Drug Administration approved a 7.2 mg dose of Wegovy in March this year.

"Rather than compete on the merits of its products, Novo is asking a court to stop Lilly from communicating the results of that trial," a Lilly spokesperson said in a statement. "We will continue to focus on the science and defend against this lawsuit vigorously."

Novo and Lilly are competing for dominance in the U.S. obesity drug market, which analysts expect to exceed US$100 billion by 2030.

Novo was first to market with weight-loss injection Wegovy but later lost the lead to Lilly's Zepbound. After replacing its chief executive and issuing multiple profit warnings last year, Novo has regained momentum with oral Wegovy, which has continued to see strong demand despite the launch of Lilly's competing pill.

Novo said it is seeking a court order requiring Lilly to withdraw the advertisements and launch a corrective advertising campaign. The company added that it plans to seek a preliminary injunction if Lilly does not voluntarily remove the ads.

It is also seeking damages, including Lilly's profits that it says can be attributed to the advertising.

Novo said it sent Lilly a cease-and-desist letter in April after U.S. regulators approved the higher 7.2-milligram dose of Wegovy. Lilly did not respond, Novo General Counsel John Kuckelman told Reuters, adding that the company instead inserted what he described as an inadequate disclaimer into the advertisements.

According to Novo, Lilly's campaign has been shown to consumers more than 700 million times since the advertisements were modified after the April letter.

Kuckelman said Lilly's advertisements compare weight-loss results of about 50 pounds for Zepbound with about 33 pounds for Wegovy, even though no head-to-head trial has compared the highest approved doses of the medicines. He said separate late-stage trials of the highest doses showed average weight loss of about 48 pounds for Zepbound and 47 pounds for Wegovy.