Novo sues Lilly over GLP-1 ad claims

On 21 July 2026 Novo Nordisk sued Eli Lilly in the United States District Court for the District of New Jersey, alleging that Lilly's national advertising for its obesity drug Zepbound and its diabetes drug Mounjaro is false and misleading^[1]. Novo says that if Lilly does not pull the campaigns voluntarily, it will ask the court for a preliminary injunction, a temporary order that would block the ads while the case is heard^[1]. Nothing has been decided yet. These are allegations in a civil complaint, and Lilly has not been found to have done anything wrong.

What Novo is alleging

Novo's core claim is that Lilly's ads line up the highest injectable doses of Lilly's own medicines against lower doses of Novo's, while leaving out newer high-dose Novo options^[1]. For weight loss, Novo points to Zepbound at 10 and 15 mg set against Wegovy at 1.7 and 2.4 mg, with no mention of the 7.2 mg high-dose Wegovy that the FDA approved in March 2026^[1]. For diabetes, it points to Mounjaro at 15 mg set against Ozempic at 1 mg, even though a 2 mg maintenance dose of Ozempic has been approved for years^[1].

Wegovy and Ozempic are Novo's brand names for semaglutide, a GLP-1 receptor agonist (a drug that mimics a gut hormone the body releases after eating to curb appetite)^[5]. Zepbound and Mounjaro are Lilly's brands for tirzepatide. Novo argues the comparison is especially misleading because no trial has tested the top doses of the two drugs directly against each other^[2].

To make its point, Novo cites its own STEP UP trial, in which the 7.2 mg dose of Wegovy produced a mean body-weight reduction of about 18.8%, roughly 47 pounds, against 3.9% on placebo^[3]. That figure, Novo says, is the context Lilly's viewers never see.

The legal hook is the Lanham Act, the federal law that lets one company sue another over false or misleading advertising. Novo says the campaigns ran where they would be hardest to miss, during major sports broadcasts and across TikTok and Facebook, and that the sheer reach is part of the harm^[3]. Comparative drug advertising is legal in the United States, but the comparison has to be accurate and not misleading, which is the exact point in dispute.

The trial at the centre of the fight

Lilly's ads lean on SURMOUNT-5, the first head-to-head trial of the two molecules. In SURMOUNT-5 (Aronne et al., New England Journal of Medicine, 2025), tirzepatide at its top doses produced a 20.2% mean body-weight reduction at 72 weeks, against 13.7% for semaglutide^[4]. The catch, for Novo, is that the semaglutide arm used 1.7 and 2.4 mg, the very doses it now calls out of date^[4].

Lilly's position is that a head-to-head trial is the fairest way to compare two medicines, and that SURMOUNT-5 is still the only randomised trial that directly compares the two in weight management^[2]. Novo does not dispute that the trial happened. Its argument is that citing a study built on lower Wegovy doses, while a stronger dose is already on pharmacy shelves, leaves viewers with a false impression. As Novo's counsel John Kuckelman put it, "ineffective, fine-print disclaimers do not fix the misleading impression created by major national campaigns"^[2].

What this is not

This is not a ruling. A complaint is one side of a story, and the court has weighed none of it yet. It is also not a safety dispute. Both semaglutide and tirzepatide are prescription medicines with large trial programmes behind them, and nobody in this case is arguing that either drug fails to produce meaningful weight loss^[4]. The fight is about how the two are compared in a 30-second spot, not about whether they work.

Novo is asking the court for a permanent injunction that would force Lilly to pull the comparative ads across every platform and to run a corrective advertising campaign^[1]. The preliminary injunction it has threatened would act faster, freezing the campaigns before a full trial. Whether the court grants it will turn on how likely Novo looks to win and how much harm the ads are said to cause in the meantime.

Practical context

The suit is the sharpest turn yet in a marketing fight between the two companies that dominate the GLP-1 market. For readers, the useful takeaway is narrow. A dose printed in a television ad is not the same as the dose you would actually be prescribed, and a comparison that looks decisive can rest on trial arms chosen years ago^[4]. This article is journalism, not medical advice, and any decision about semaglutide or tirzepatide belongs with a clinician who knows your history.

What happens next is procedural. Novo still has to file its preliminary-injunction motion, Lilly gets to respond, and a judge decides whether to freeze the ads before trial. If the campaigns keep running in the meantime, expect both sides to keep citing the same trial to opposite ends. The dose facts themselves are not really in question. What the court has to sort out is whether Lilly's way of presenting them crosses the line from aggressive into misleading^[1]. We will update this page as the New Jersey court acts.