A legal battle between two pharmaceutical giants has escalated, with Novo Nordisk filing a false advertising lawsuit against Eli Lilly in U.S. federal court. The Danish drugmaker alleges that Lilly's marketing for its weight-loss and diabetes treatments relies on misleading comparisons that inflate efficacy claims. Main Developments Novo Nordisk announced Tuesday it had sued Eli Lilly in the U.S. District Court in New Jersey, accusing the American company of violating federal and state false advertising and unfair competition laws, including the Lanham Act. The lawsuit specifically targets Lilly's nationwide campaigns for obesity drug Zepbound and diabetes treatment Mounjaro. At the heart of the dispute is how Lilly compares its medicines to Novo's products. Novo alleges that Lilly's advertisements contrast the highest approved doses of Zepbound and Mounjaro with lower doses of Novo's Wegovy and Ozempic, while omitting newer, higher-dose versions that Novo says deliver greater weight loss. Read also: Indian Oil Corp Halts Iraq Oil Lift Amid Strait of Hormuz Risks Background Novo Nordisk sent a cease-and-desist letter to Eli Lilly in April, shortly after U.S. regulators approved a 7.2-milligram dose of Wegovy. According to Novo's general counsel John Kuckelman, Lilly did not respond to the letter but instead inserted what he described as an inadequate disclaimer into the advertisements. Kuckelman told Reuters that Lilly's ads claim weight-loss results of about 50 pounds for Zepbound compared with about 33 pounds for Wegovy. However, no head-to-head trial has compared the highest approved doses of the two medicines. Separate late-stage trials of the highest doses showed average weight loss of about 48 pounds for Zepbound and 47 pounds for Wegovy, Kuckelman said. Why It Matters The lawsuit underscores the fierce competition in the lucrative weight-loss drug market, where both companies are vying for dominance. Misleading advertising claims could influence prescribing decisions and patient choices, potentially affecting billions in revenue. The case also tests how courts interpret comparative drug marketing under the Lanham Act. What's Next Novo Nordisk is seeking a court order requiring Eli Lilly to withdraw the advertisements and run a corrective advertising campaign. If Lilly does not voluntarily remove the ads, Novo plans to seek a preliminary injunction. The case will likely hinge on whether Lilly's comparisons are deemed materially misleading under federal law.