A new study has reaffirmed that Eli Lilly's (LLY) GLP-1 drugs fare better for weight loss than Novo Nordisk's (NVO).

The study, conducted by researchers at hospital systems in Washington and Oregon and published by JAMA, showed that over a period of a year, patients on Novo Nordisk's diabetes drug Ozempic lost 8% of their body weight compared to 15% from Eli Lilly's diabetes drug Mounjaro. It also showed that over the course of a year, patients on Eli Lilly's drug continuously lost more weight, compared to decreased weight loss over time from Novo Nordisk's drug — 42% versus 18%, respectively, lost 15% or greater weight.

The study lightly pressured Novo Nordisk's stock Tuesday, which traded down more than 2% at the bell.

In a statement to Yahoo Finance, Novo claimed it wasn't a fair apples-to-apples comparison and that the study had some key deficiencies.

"Novo Nordisk welcomes independent research investigating the safety and clinical utility of our products. However, the ideal way to compare two treatments is an adequately powered head-to-head randomized clinical trial (RCT) in obesity.

Currently, no head-to-head trials have been completed comparing tirzepatide and semaglutide," a spokesperson said in an emailed statement.

They noted in particular that the study looked at the diabetes drugs of each company, Ozempic for Novo and Mounjaro for Lilly, which have less potent doses since their goal isn't weight loss.

The weight-loss drugs for each company, Wegovy and Zepbound, respectively, include higher doses of the formula in order to achieve greater weight loss.

Eli Lilly did not want to comment on the study. Instead, the company is awaiting its own head-to-head trial.

"As Lilly was not involved in and did not sponsor this study, we are unable to provide comment. However, we are studying tirzepatide and semaglutide in participants with obesity in a phase 3b head-to-head trial, SURMOUNT-5, that is expected to complete later this year," a spokesperson said in an emailed statement.

The study confirms the initial impression of both companies' Phase 3 data. They already showed Lilly's tirzepatide drugs do slightly better with weight loss than Novo's semaglutide — achieving as much as 21% versus 12%-14% weight loss.

Lilly has already used this data in its advertising for Mounjaro, claiming Mounjaro has "unmatched weight reduction across all 3 doses vs Ozempic."

An imperfect study

Using patient data from Truveta, which hides identifiable information, researchers looked at an initial set of 44,000 patients and whittled it down to more than 9,000 to try and compare patients who seemed to have similar characteristics.

They included obese patients, half of which were diabetic. Dr. F. Perry Wilson, the director of the clinical and translational research accelerator at Yale University, noted on X that within the initial data set, "Those who got Mounjaro were, broadly, healthier, richer, more educated, more white."

But, Novo points out, the study also did not include "insurance type, socioeconomic status, baseline BMI (only baseline weight was compared and matched), frequency of interactions between patients and HCPs [health care practitioners], concomitant use of other medications with weight changing effect, among others."

The researchers said in the study that they focused on patients who went for follow-up visits to health centers and those whose information was complete (including gender) — patients with missing information were not included.

GLP-1s have taken the market by storm, leading to billions of additional revenue for the companies in the past year, and Wall Street expects these once-weekly injectables to contribute between $13 billion and $25 billion to Novo and Lilly's bottom lines this year.

Anjalee Khemlani is the senior health reporter at Yahoo Finance, covering all things pharma, insurance, care services, digital health, PBMs, and health policy and politics. Follow Anjalee on all social media platforms @AnjKhem.

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