Amgen‘s stock rose more than 12% on Friday after the drugmaker teased positive initial data on its experimental weight loss injection. 

That fueled investor concerns about new competition in the rapidly growing weight loss drug industry, sending shares of the current obesity players, Novo Nordisk and Eli Lilly, lower on Friday. Eli Lilly shares dropped nearly 3%, while Novo Nordisk’s U.S.-traded shares fell more than 1%.

Novo Nordisk’s stock was already under pressure on Thursday after sales of its blockbuster weight loss injection Wegovy missed analysts’ estimates for the first quarter due to lower pricing. 

During a first-quarter earnings call Thursday, Amgen’s CEO Bob Bradway said he was “very encouraged” by early results from a mid-stage study on the company’s obesity injection, MariTide. Investors have been laser-focused on that drug and the rest of Amgen’s weight loss drug pipeline as it races several other drugmakers to join the booming market. 

“We are confident in MariTide’s differentiated profile and believe it will address important unmet medical needs,” Bradway said during the call. 

Amgen did not provide specific data, but its Chief Scientific Officer Jay Bradner said that patient dropout has not been an issue. He said Amgen is on track to release initial data from the study in late 2024 and is also planning late-stage studies in patients with obesity, obesity-related conditions and diabetes. 

Bradway also highlighted the potential competitive advantages of the injection, which patients will take using a hand-held autoinjector once a month or even less frequently. That could offer far more convenience than the weekly injections on the market, Novo Nordisk’s Wegovy and Eli Lilly’s Zepbound. 

“While there has been significant debate on the potential efficacy and safety of MariTide since the initial disclosures of the Phase I data in 2022, we have grown more confident in the potential for the therapy to meaningfully differentiate from other therapies in development, particularly in regard to treatment intervals,” William Blair analyst Matt Phipps said in a research note on Friday, adding that the firm is upgrading its rating on Amgen shares to “outperform.” 

Notably, Amgen said it was scrapping its experimental oral obesity drug. But that development was not as important as the MariTide update, Jefferies analyst Michael Yee said in a research note Thursday. 

Amgen’s Bradway said the company has started expanding manufacturing for MariTide. That’s a signal that the company is preparing to produce enough supply of the drug – a major issue that Novo Nordisk and Eli Lilly have grappled with over the past year and a half. 

Still, investors were pleased with Eli Lilly on Tuesday after the company assured them it can overcome ongoing supply constraints for its popular drugs. Eli Lilly hiked its full-year guidance in part due to optimism around increased production of Zepbound, its diabetes injection Mounjaro and similar drugs for the rest of the year.

Eli Lilly has several manufacturing sites either “ramping up or under construction,” including two locations in North Carolina, two in Indiana, one in Ireland and one in Germany, along with a seventh recently acquired site, executives said during an earnings call. 

Meanwhile, investors were less impressed with Novo Nordisk on Thursday. 

Sales of Wegovy during the first quarter nearly doubled, but came in under analysts’ expectations. That signals Novo Nordisk is struggling to meet demand for the treatment. 

But Novo Nordisk also pointed to fierce competition from Eli Lilly’s Zepbound, which has shaken up pricing dynamics for Wegovy in the U.S. 

“Net pricing” for both Wegovy and Ozempic will be lower in the U.S. throughout the year due to the “increasing volume and competition,” Chief Financial Officer Karsten Munk Knudsen said on a first-quarter earnings call on Thursday.