Lilly's Mounjaro triggers more weight loss than Novo Nordisk's Ozempic: study

Is Eli Lilly’s Mounjaro or Novo Nordisk’s Ozempic more effective in helping patients lose weight?

While a head-to-head trial pitting the two treatments remains ongoing, new evidence shows that Lilly’s tirzepatide may be the superior weight loss product.

In examining the electronic records of more than 18,000 overweight or obese adults in the United States, health data analytics company Truveta found that Lilly’s tirzepatide helped patients lose more weight than Novo’s semaglutide, with the effects growing over time.

Results of the study, which looked at data from May of 2022 and September of 2023, were published Monday in the JAMA Internal Medicine monthly review.

After use of tirzepatide for three months, patients lost an average of 5.9% of their body weight compared to 3.6% for semaglutide. Over a year’s time, those on tirzepatide lost an average of 15.3% of their body weight compared to 8.3% for semaglutide users.

Additionally, tirzepatide patients were much more likely to lose 15% of their body weight than those using semaglutide. While 42% of those on tirzepatide reached the benchmark after one year of treatment, only 18% of those on semaglutide could say the same.

Novo Nordisk pointed to several shortfalls in the study, including that the drugs analyzed are approved for diabetes, not obesity. The analysis also does not provide sufficient information on the dosages used at the initiation and completion of treatment. 

"The ideal way to compare two treatments is an adequately powered head-to-head randomized clinical trial in obesity," Novo added.

Lilly’s tirzepatide is the active ingredient found in its diabetes product Mounjaro and its obesity treatment Zepbound, while Novo’s semaglutide is the compound used to make its diabetes blockbuster Ozempic and its obesity follow-on Wegovy.

Importantly, the Truveta study looked at the drugs that are approved for diabetes. The authors noted that "future studies are needed to compare versions labeled for weight loss."

While cross-trial comparisons are often framed as unreliable, separate clinical studies on tirzepatide and semaglutide have already suggested that Lilly’s drug is more effective in helping patients lose weight.

While Lilly’s trial for Zepbound showed an average body weight loss of 21% over 72 weeks, Novo’s study for Wegovy produced an average weight loss of 15% through 68 weeks.  

More conclusive data will be available when Lilly reports on its SURMOUNT-5 trial comparing the two drugs in 700 participants from around the world. The study kicked off in April of last year and measures treatment effects over 72 weeks.  

While semaglutide regulates the glucagon-like peptide-1 (GLP-1) incretin hormone, tirzepatide acts on both the GLP-1 and the gastric inhibitory polypeptide (GIP) hormones. Both are involved in the production of insulin and the control of appetite.

Novo was first to the market with Ozempic, which gained FDA approval in 2017. It generated $4.3 billion in sales in the first quarter of this year. Meanwhile, Mounjaro, which was approved in 2022, is gaining ground quickly. Lilly reported its sales at $1.8 billion in the first quarter.

"Mounjaro's novel dual mechanism not only underscores its clinical value but also its potential to become the top-selling drug in its category by 2029," GlobalData analyst Ieni Tokali, predicted in April.

EDITOR'S NOTE: A statement from Novo Nordisk was added to this story.