Amgen stock falls on weight loss drug's bone density loss data

Shares of Amgen fell more than 7% on Tuesday as analysts examined bone density loss data from an early study of MariTide, an experimental weight-loss injection.

An analyst said the additional data suggests a new potential safety risk associated with the drug. But others said the stock move was an overreaction and that more data on a larger patient population was needed.

Amgen did not immediately respond to a request for comment on the data

The drug is a promising potential competitor in the weight loss drug market. It is designed to be taken monthly, rather than once a week, as is the case with previous injections Novo Nordisk And Eli Lillyand promotes weight loss differently.

Wall Street is awaiting crucial results from MariTide's Phase 2 trial, which are expected to be released before the end of the year.

Analysts on Tuesday cited additional publicly available data from a Phase 1 trial showing that the highest dose of MariTide – 420 milligrams – was associated with a loss in bone mineral density of about 4% over a 12-week period. A decrease in bone mineral density means the bones lose calcium and other minerals, making them weaker and increasing the likelihood of fracture.

In a research note, Cantor-Fitzgerald analyst Olivia Brayer called the data a “big unknown” and suggested it could be a potential risk related to drugs like MariTide, which work through so-called GIPR antagonism. Amgen's injection blocks a gut hormone receptor called GIP but also activates another appetite-stimulating hormone called GLP-1.

This is different than Eli Lilly's obesity drug Zepbound, which activates GIP and GLP-1. Wegovy activates GLP-1 but does not target GIP, which can also affect how the body breaks down sugar and fat.

“On the one hand, patients may naturally lose bone mineral density during weight loss treatment,” Brayer wrote.

But Brayer said, “On the other hand, this could be a failure because there appears to be a dose-dependent increase” in bone mineral density loss. This means that the higher the dose patients take, the more bone mineral density they appear to lose.

Meanwhile, Jefferies analyst Michael Yee wrote in a note that the additional MariTide data appears to be “a non-issue.” Yee acknowledged that there was a decrease in bone density in people who took the highest dose of the drug, but said, “The data is patchy.”

For example, he pointed to data on a lower dose of the drug that showed bone density actually increased by 1% before normalizing. Yee added that “changes” in bone mineral density are a known side effect of weight-loss medications in the first one to three months of use, as people lose significant weight quickly.

Amgen is also aware of the “hypothetical concern” about loss of bone mineral density, Yee said, citing the company's discussions with management.

“While we are of course not saying there is no impact, we are saying that we do not believe there is a significant problem.” [bone mineral density] “Overall, we don’t think there is a problem and the effect will normalize over time.”

BMO analyst Evan Seigerman wrote in a note on Tuesday: “We would be cautious in making a comprehensive judgment about MariTide's safety profile based on these data.”

He added: “It would be easier for us to assess the safety profile on a larger cohort of patients.” There may not be a clear answer until Amgen releases full Phase 2 trial data on the drug.

“This has not changed our opinion of MariTide and we consider the sale to be excessive,” Seigerman wrote.