Novo Nordisk (NVO Quick QuoteNVO - Free Report) has filed a lawsuit against Eli Lilly (LLY Quick QuoteLLY - Free Report) , accusing its rival of misleading high-profile U.S. advertising campaigns to promote its blockbuster injectable GLP-1 medicines, Zepbound and Mounjaro, over NVO’s injectable semaglutide medicines, Wegovy and Ozempic for obesity and type II diabetes (T2D), respectively.

The legal challenge comes at a pivotal time as the global obesity market has emerged as one of the pharmaceutical industry's most fiercely contested arenas. While the dispute centers on comparative advertising, it carries broader strategic significance, highlighting the intensifying battle between the two GLP-1 leaders, where physician and patient perceptions can be as critical as clinical efficacy in shaping prescribing decisions and market share.

NVO Challenges LLY’s Comparative GLP-1 Advertising Claims

Earlier this week, Novo Nordisk filed a lawsuit against Eli Lilly in a U.S. federal court, alleging that the company's nationwide direct-to-consumer advertising campaigns for Zepbound and Mounjaro are misleading because they rely on outdated clinical comparisons while omitting newer evidence supporting higher-dose Wegovy.

The dispute centers on Lilly's advertisements highlighting results from the SURMOUNT-5 head-to-head study, where Zepbound achieved an average weight loss of 20.2% compared with 13.7% for Wegovy after 72 weeks. Those findings compared Zepbound's highest doses with Wegovy's then-approved maximum dose of 2.4 mg and were scientifically valid when generated.

Year to date, Novo Nordisk shares have lost 2.9% against the industry’s 8.9% growth.

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However, the competitive landscape changed in March 2026 when the FDA approved Wegovy 7.2 mg, a higher-dose formulation that demonstrated approximately 19% (~47 pounds) average weight loss in the STEP UP study. Novo Nordisk argues that Lilly's continued use of earlier comparisons creates the misleading impression that Zepbound is categorically more effective, despite the availability of a newer FDA-approved dose that substantially narrows the efficacy gap.

NVO also alleges that Lilly's Mounjaro advertisements compare the drug's highest approved 15 mg dose with only the 1 mg maintenance dose of Ozempic, while omitting the FDA-approved 2 mg dose, which has been available for more than four years and offers greater efficacy. The lawsuit follows LLY’s refusal to withdraw or substantially revise the advertisements despite receiving a formal cease-and-desist notice from Novo Nordisk. The company is seeking a permanent injunction requiring LLY to withdraw the advertisements and launch corrective marketing.

A Fight Over Perception Could be Just as Important as Efficacy

Novo Nordisk’s lawsuit appears to be less about challenging the original SURMOUNT-5 data than about redefining the narrative in an increasingly competitive obesity market. Lilly has built considerable commercial momentum by positioning Zepbound as the most effective weight-loss therapy available, a perception reinforced through broad consumer advertising.

If the court ultimately prevents Lilly from continuing to make superiority claims based on comparisons that exclude Wegovy's latest approved dose, Novo Nordisk could gain an important strategic advantage. While the efficacy gap may not disappear entirely, restricting these advertisements could weaken one of LLY’s strongest commercial messages and help NVO reshape physician and patient perceptions around Wegovy's competitiveness.

Even so, investors should recognize that any legal victory would likely offer only a partial competitive benefit. Lilly possesses enormous marketing resources and would almost certainly redesign its advertising strategy to comply with any court ruling while continuing to emphasize other differentiating features of its portfolio. The broader competition will still be determined by clinical outcomes, product launches, pricing, reimbursement and manufacturing capacity rather than advertising alone.

Novo Nordisk A/S Price and Consensus

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NVO Signals It Is Ready to Defend Its GLP-1 Franchise

Novo Nordisk has indicated that it intends to seek a preliminary injunction in the coming days if Eli Lilly does not voluntarily withdraw the advertisements. That move underscores the urgency with which the company views protecting Wegovy's market position as competition intensifies.

The lawsuit highlights that Novo Nordisk is prepared to defend its obesity franchise not only through product innovation but also through legal and commercial channels. While the outcome is unlikely to alter the long-term competitive dynamics by itself, a favorable ruling could help narrow the perception gap that has increasingly favored Zepbound, as both companies continue battling for leadership in one of healthcare's fastest-growing markets.

NVO Faces Rising Competitive Pressure Beyond LLY in GLP-1s

The immense market opportunity in obesity treatments is also attracting smaller biotech firms, like Viking Therapeutics (VKTX Quick QuoteVKTX - Free Report) and Structure Therapeutics (GPCR Quick QuoteGPCR - Free Report) , which are advancing their GLP-1–based therapies to challenge the incumbents. Viking Therapeutics’ dual GIPR/GLP-1 receptor agonist, VK2735, is being developed as both oral and subcutaneous formulations for the treatment of obesity. Viking Therapeutics plans to advance oral VK2735 into phase III development for obesity in the fourth quarter of 2026.

Structure Therapeutics’ phase II ACCESS study on its orally administered GLP-1 RA, aleniglipron, demonstrated significant weight loss across all doses. Structure Therapeutics expects to initiate the late-stage program of aleniglipron in obesity in the second half of 2026.

NVO’s Zacks Rank & Stocks to Consider

Novo Nordisk currently carries a Zacks Rank #5 (Strong Sell).

You can see the complete list of today’s Zacks #1 Rank (Strong Buy) stocks here.