LONDON, July 21 - Novo Nordisk sued rival Eli Lilly in a U.S. federal court on Tuesday, accusing the U.S. drugmaker of false advertising in claiming its weight-loss medicines outperform Novo's drugs.

The Danish company filed the lawsuit 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.

Indianapolis-based Eli Lilly did not immediately respond to a request for comment.

"The ads are maliciously and deceptively false because Lilly knowingly cites outdated clinical trials that compare the highest doses of the Lilly medicines to lower doses of Novo Nordisk’s medicines," Novo wrote in its complaint.

Novo and Lilly are locked in a fierce battle for dominance in the U.S. obesity drug market, which analysts expect to be worth more than $100 billion by 2030.

Novo was first to market with weight-loss injection Wegovy, but later lost the lead to Lilly's rival Zepbound. After replacing its CEO and issuing multiple profit warnings last year, Novo has landed a counterpunch with oral Wegovy, whose strong demand has held up despite the launch of Lilly's competing pill.

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

Novo is also seeking damages, including Lilly's profits that can be attributed to the ads.

Shares of Eli Lilly fell 0.5% to $1141.84 in pre-market U.S. trade, while Copenhagen-listed Novo Nordisk shares were down 1.7% in afternoon trading.

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