Novo Nordisk filed a lawsuit in a US federal court in New Jersey on Tuesday, accusing Eli Lilly of deceptive advertising for its weight-loss and diabetes drugs. The Danish company alleges that Lilly’s national campaigns for Zepbound and Mounjaro falsely claim greater efficacy than Novo’s Wegovy and Ozempic by comparing the highest approved doses of Lilly’s medicines with lower, outdated doses of Novo’s products. The legal filing states that Lilly’s ads cite a 50-pound average weight loss for Zepbound against 33 pounds for Wegovy, while omitting a newer, higher-dose version of Wegovy that Novo says delivers an average loss of 47 pounds—nearly identical to the 48 pounds seen in Lilly’s most rigorous trial.

According to the Danish company, the advertising campaign has generated more than 700 million impressions since late April, creating what it calls a “misleading impression” of superiority. Novo Nordisk says it sent a cease-and-desist letter after US regulators approved a 7.2 mg dose of Wegovy in March, but Lilly merely added a footnote to its television ads. The lawsuit seeks a court order to pull the advertisements and run a corrective campaign, as well as damages. Eli Lilly, headquartered in Indianapolis, countered that its advertising is “truthful, transparent, and grounded in the most direct scientific evidence available,” and vowed to defend itself vigorously. The US company argues that its comparison trial was robustly designed and that Novo is attempting to block communication of those results.

The legal clash reflects the high stakes in the global obesity drug market, which analysts in the United States project will exceed $100 billion annually by 2030. Novo Nordisk, once the clear leader with Wegovy, has seen its market share erode as Lilly’s Zepbound gained ground; financial analysts note that Lilly now captures a greater share of US prescriptions. The dispute also unfolds as these GLP-1 drugs reshape consumer behaviour: a Cornell University study cited in Brazilian press reports found that US households with at least one user cut grocery spending by an average of 5.3%, with sharper drops in snacks and fast food, while spending on healthier items and fitness increased. This wider economic ripple effect intensifies the commercial imperative for both companies to secure brand loyalty.

Novo Nordisk has indicated it will seek a preliminary injunction if Lilly does not voluntarily withdraw the advertisements. The case, filed under the Lanham Act and state unfair competition laws, will now proceed in federal court. European industry observers note that direct-to-consumer drug advertising, permitted in the US but restricted in most other markets, amplifies the impact of such comparative claims. The outcome could set a precedent for how pharmaceutical companies may market competing products in a sector where incremental dosing improvements can shift the narrative of efficacy.