GLP-1 weight loss drugs, including a zepbound KwikPen and wegovy injection, are photographed on a table at the Long Island Weight Loss Institute in Port Jefferson Station, New York, on June 26, 2026. (Photo by Karsten Moran / For The Washington Post …
Novo Nordisk is suing Eli Lilly over its GLP-1 ads, accusing the rival drugmaker of false advertising for claiming Lilly’s Mounjaro and Zepbound outperform Novo’s Ozempic and Wegovy.
The lawsuit was filed Tuesday in U.S. District Court in New Jersey.
Novo Nordisk vs. Eli Lilly
The lawsuit accuses Lilly of knowingly using outdated clinical trials that compare the highest doses of Mounjaro and Zepbound to the lowest doses of Ozempic and Wegovy. Novo Nordisk also disputes Lilly’s claims that Mounjaro for Type 2 diabetes "reduces A1c significantly more than" Ozempic.
What they're saying:
"Lilly’s messages to consumers are deliberately simple and deliberately false," the complaint states.
"Lilly intentionally relies on outdated clinical trials to paint a false and misleading picture about the effectiveness of Novo Nordisk’s medicines."
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The lawsuit accuses Lilly of violating federal and state false advertising and unfair competition laws, including the Lanham Act.
The other side:
Eli Lilly sent the following statement to FOX Local in response to the lawsuit:
"The gold standard for comparing medicines is a robustly designed, well-conducted head-to-head clinical trial — like SURMOUNT-5, which remains the only head-to-head, randomized clinical trial directly comparing tirzepatide and semaglutide in weight management," the statement reads.
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"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."
Zepbound vs. Wegovy
Big picture view:
Zepbound and Wegovy are both GLP-1 drugs approved for weight loss, but Zepbound targets two hormones, GIP and GLP-1, while Wegovy only targets GLP-1. Zepbound is also FDA-approved to treat sleep apnea in patients with obesity, while Wegovy is FDA-approved to treat cardiovascular disease.
By the numbers:
According to a study funded by Eli Lilly and published in the New England Journal of Medicine in 2025, people taking Zepbound lost nearly 50% more weight than those using rival Wegovy. It was billed as the first head-to-head study of the blockbuster drugs.
Clinical trial participants who took Zepbound lost an average of 50 pounds over 72 weeks, while those who took semaglutide, or Wegovy, lost about 33 pounds.
Dig deeper:
In the lawsuit, Novo Nordisk counters that those studies were done before the Food and Drug Administration approved the "newest, more effective doses" of Wegovy and Ozempic.
"In fact, there are no head-to-head clinical trials comparing the highest doses of the respective medicines, so Lilly has no basis to make these" claims, Novo Nordisk wrote in the complaint.
How do GLP-1 drugs work?
The backstory:
GLP-1s, a class of drugs that include semaglutide (Ozempic, Wegovy) and tirzepatide (Mounjaro and Zepbound), were initially prescribed to treat Type 2 diabetes, but have soared in popularity because of weight loss. Wegovy and Zepbound are FDA approved for weight loss, while Ozempic and Mounjaro are approved for Type 2 diabetes.
The drugs work by mimicking the actions of hormones, found primarily in the gut, that kick in after people eat. The hormones help regulate blood sugar by triggering the pancreas to release insulin, another hormone, and slowing the release of sugar from the liver. People who are overweight or have obesity can become insulin-resistant, which means the body doesn’t respond to insulin properly.
The obesity drugs lower blood sugar and slow down digestion, so people feel full longer. They also affect signals in the brain linked to feelings of fullness and satisfaction, tamping down appetite, food-related thoughts and cravings.
Because people feel full longer, they eat less and lose weight.
However, it appears that if people taking the drugs stop, most regain the weight they lost — and the health problems that come with weight gain.
The Source: This article includes information from Novo Nordisk’s federal lawsuit against Eli Lilly and previous FOX Local reporting. The Associated Press contributed.