Novo Nordisk Sues Eli Lilly Over Alleged Misleading Weight-Loss Drug Ads

Novo Nordisk has filed a federal lawsuit against its primary rival, Eli Lilly, accusing the company of executing a misleading advertising campaign that falsely claims its weight-loss and diabetes treatments are superior to Novo’s competing products.

The lawsuit, filed on Tuesday in the U.S. District Court for the District of New Jersey, centers on advertisements for Eli Lilly’s blockbuster medications, Zepbound and Mounjaro. According to Novo Nordisk, these promotional materials deceive consumers by comparing the maximum dosages of Lilly’s drugs against lower, less potent doses of Novo Nordisk’s Wegovy and Ozempic. Novo Nordisk characterized the campaign as “maliciously and deceptively false,” asserting that Lilly knowingly relied on outdated clinical data to skew the comparison in its favor.

In response, Eli Lilly has firmly rejected the allegations, defending its marketing practices as scientifically sound. A spokesperson for the Indianapolis-based pharmaceutical giant stated that the advertisements are based on the results of its SURMOUNT-5 clinical trial, which concluded in 2024. The trial directly compared patients taking 10 mg or 15 mg doses of Zepbound with those prescribed 1.7 mg or 2.4 mg doses of Wegovy.

Lilly described the SURMOUNT-5 study as the “gold standard” for comparing the two treatments, noting it remains the only randomized, head-to-head clinical trial directly evaluating tirzepatide—the active ingredient in Zepbound and Mounjaro—against semaglutide, the active ingredient in Wegovy and Ozempic, for weight management. The company argued that Novo Nordisk is attempting to use the legal system to suppress scientific data rather than competing on product merit.

However, the regulatory landscape for these medications has shifted. In March, the U.S. Food and Drug Administration approved a higher 7.2 mg maintenance dose of Wegovy. Novo Nordisk contends that this approval renders Lilly’s comparative advertising obsolete and misleading, as it fails to account for the newly authorized higher dosage of its treatment.

The legal dispute marks a significant escalation in the battle for dominance over the lucrative U.S. obesity market. With obesity rates remaining high, demand for GLP-1 receptor agonists has surged globally. Financial analysts project that the market for these highly sought-after weight-loss medications could exceed $100 billion by the end of the decade. The immense demand has previously triggered widespread supply shortages for both manufacturers, prompting both Novo Nordisk and Eli Lilly to ramp up manufacturing capacity and take legal action against compounding pharmacies distributing unauthorized copies of their patented drugs.

Novo Nordisk claims it attempted to resolve the advertising dispute out of court, sending a cease-and-desist letter to Lilly in April. After receiving no response, Novo Nordisk filed the lawsuit, noting that Lilly’s revised advertisements have been viewed more than 700 million times since late April.

Through the lawsuit, the Danish drugmaker is seeking a court order to force Lilly to halt the advertising campaign and run corrective advertisements. Additionally, Novo Nordisk is seeking financial damages, including any profits Lilly may have generated as a direct result of the disputed promotional materials.