In heavyweight obesity fight, Eli Lilly launches Mounjaro head-to-head trial against Novo Nordisk's Wegovy

The stakes are getting even higher in the fight for supremacy between Eli Lilly and Novo Nordisk in the multibillion-dollar obesity market.

Eli Lilly on Friday quietly registered a new phase 3b trial on The study, coded SURMOUNT-5, will pit Lilly’s Mounjaro against Novo’s weight loss drug Wegovy in obese patients or those who’re overweight with weight-related health conditions.

The trial aims to enroll 700 participants from 61 sites in the U.S., Canada, South America and several European countries, according to the post. The study is expected to kick off next Friday and last for about 78 weeks, with an estimated primary completion date in February 2025.

On the study’s primary endpoint, investigators will compare the percentage weight loss from baseline between the two drugs after 72 weeks. It’s not immediately clear whether Lilly plans SURMOUNT-5 as a superiority study to show if Mounjaro is better than Wegovy, or if the company just wants to show noninferiority. Other secondary measurements include the percentage of patients who’ve achieved certain magnitude of weight loss. 

Lilly didn’t immediately respond to a Fierce Pharma request for comment.

The new study comes as both drugs have gained much fanfare thanks to Hollywood stars, an unexpected promotion by Twitter owner Elon Musk and other viral posts on social media. Surging demand drove both drugs into short supply for months, but the companies recently resolved the shortages.

The huge unmet need in weight loss has spurred megablockbuster sales projections. Last fall, analysts at UBS projected Mounjaro could reach a jaw-dropping $25 billion in peak sales with uses in diabetes in obesity, although other more cautious analysts have put the potential at or below $10 billion.

In a report in November, Cowen analysts estimated that the global obesity drug market could reach $30 billion by 2030, with Novo and Lilly leading the charge. An earlier Morgan Stanley research put the number at $50 billion.

While Wegovy, or semaglutide 2.4mg once weekly, won an FDA approval for chronic weight management in obese and certain overweight patients in 2021, Lilly’s Mounjaro, also known as tirzepatide, is currently only approved to treat Type 2 diabetes.

Lilly recently initiated a rolling FDA submission for Mounjaro in obesity, with a goal to launch later this year. Lilly might use a different brand name for tirzepatide in obesity, just as how Novo’s semaglutide injection goes by the commercial moniker Ozempic in diabetes.

To be eligible for the new SURMOUNT-5 trial, a patient must either have a body mass index (BMI) of at least 30kg/m2 or at least 27kg/m2, accompanied by a prior diagnosis of at least one of four weight-related disorders: hypertension, dyslipidemia, obstructive sleep apnea, and cardiovascular disease. The criteria match Wegovy’s current FDA-approved patient population.

The timing of SURMOUNT-5’s launch also matches an expected imminent readout of SURMOUNT-2, the second of two phase 3 trials that Lilly aims to use to win an FDA approval for Mounjaro in obesity. An update to SURMOUNT-2’s status on suggests that the study wrapped up on April 10.

Wegovy belongs to the GLP-1 agonist drug class, while Mounjaro is a dual GLP-1/GIP agonist, which theoretically could trigger a stronger weight loss effect.

In the first of its two obesity phase 3 trials to read out, Mounjaro delivered a weight reduction of up to 21% in non-diabetic patients in the SURMOUNT-1 trial. By comparison, Wegovy chalked up an average weight loss of 15%—or a 12.4% difference from placebo—in its own trial in patients without diabetes.

However, without a head-to-head study, no one can say for certain how Wegovy fares in comparison with Mounjaro. And that’s what the new SURMOUNT-5 trial aims to find out.

Two other phase 3 trials for Mounjaro in obesity are also expected to report results soon. SURMOUNT-3 is coupling Mounjaro with intensive lifestyle modification therapy, and SURMOUNT-4 is evaluating the benefit of continued Mounjaro treatment. Both those two studies have passed their primary completion dates by a few days, but their posts have yet to show their completion as of Friday.

Meanwhile, in anticipation of substantial demand for its diabetes and obesity products, Lilly has been expanding its manufacturing capacity aggressively. These projects include a planned record-breaking $3.7 billion investment in two new active pharmaceutical ingredients sites at the LEAP Innovation Park in Indiana.

Another $1.7 billion is earmarked for a plant dedicated to diabetes and obesity drugs at Research Triangle Park in North Carolina.