Novo Nordisk has filed a lawsuit against Eli Lilly, accusing its fellow obesity drug titan of peddling false advertising claiming higher efficacy over respective obesity and diabetes products.
In a lawsuit filed in the US, Danish drugmaker alleged that Lilly’s campaign was designed to mislead consumers of the “comparative efficacy” of weight loss and type 2 diabetes drugs in the companies’ respective portfolios. The company claims it did this through a “nationwide pattern of deceptive advertising”.
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The claim boils down to Novo alleging that Lilly’s direct-to-consumer advertising campaign pointed to outdated clinical studies to convey a misleading picture to patients. Novo argued that this was done to show that Lilly’s tirzepatide outperformed its own product, semaglutide, in terms of average weight loss.
Tirzepatide is approved in the US under the brand names Mounjaro and Zepbound for type 2 diabetes and weight loss, respectively, while semaglutide is branded as Ozempic and Wegovy in the same indications.
In a statement, Novo said: “This action follows Lilly’s refusal to pull down or meaningfully correct certain ads, despite a formal cease-and-desist request from Novo Nordisk.”
The lawsuit outlines Novo seeking a permanent injunction requiring Lilly to pull down its misleading comparative advertising across all platforms and to conduct a corrective advertising campaign.
Novo’s particular qualm is Lilly’s decision to omit data that includes the highest dose of injectable Wegovy at 7.2mg. This dose led to an average weight loss of 19% in studies. Zepbound’s highest dose led to around 20.9% average weight loss. No controlled head-to-head clinical trial between the highest doses of the two medicines has been conducted, making fair comparisons hard to conclude.
John Kuckelman, senior vice president and group general counsel, Novo Nordisk, said: “Healthcare companies have a responsibility to keep their public claims accurate and current — ineffective, fine-print disclaimers do not fix the misleading impression created by major national campaigns.”
A Lilly spokesperson pointed Pharmaceutical Technology to the SURMOUNT-5 study (NCT05822830), which compared 10mg or 15mg tirzepatide to semaglutide 1.7mg or 2.4mg. Data from this pointed to tirzepatide’s higher efficacy.
The spokesperson added: “Rather than compete on the merits of its products, Novo is asking a court to stop Lilly from communicating the results of that trial. We stand firmly behind our advertising. It is truthful, it is transparent, and it is grounded in the most direct scientific evidence available — exactly what patients deserve. We will continue to focus on the science and defend against this lawsuit vigorously.”
The lawsuit marks the latest flashpoint between the two titans of the weight loss drug landscape. Novo is vying to gain back market share in the space after Eli Lilly’s successful portfolio growth. Revenue for the drugmaker in Q1 2026 reached $19.8bn, a surge of 56% from the same period last year, buoyed by continued sales growth for its injectable weight loss drugs.
Novo is pinning much of its near-term growth on oral obesity drug offerings. Last week, Novo gained European approval for oral Wegovy, which follows similar decisions in the US and UK for the pill, meaning Novo has gained a first-mover advantage over its rival in all three territories.
The lawsuit also comes amid heightened focus on drug advertising in the US. In September 2025, President Donald Trump tasked health secretary Robert F Kennedy Jr (RFK Jr) with a clamp down on misleading direct-to-consumer (DTC) prescription drug adverts.
At the time, Trump blamed the weakening of US Food and Drug Administration (FDA) requirements over time, which he said had allowed drug companies to include less information, particularly in broadcast advertising. Marty Makary, the former FDA commissioner, admitted that decades of regulatory failure were to blame for misleading pharma ads.
Since Trump’s request, the FDA has sent more than a hundred letters to pharmaceutical companies either warning or demanding a stop to misleading and deceptive ads. Many of these have come in the obesity drug realm.
