Dive Brief:Amgen on Tuesday said its weight loss drug MariTide helped people with obesity lose up to 20% of their body weight over one year in a Phase 2 trial, paving the way for the company to initiate a larger study aimed at supporting U.S. approval.The weight loss Amgen reported for its monthly shot appeared to be in line with the popular obesity drugs Zepbound and Wegovy, Wall Street analysts said. However, the rate of trial participants discontinuing MariTide appeared higher than what was reported in testing for those weekly medicines, sold by Eli Lilly and Novo Nordisk.Amgens study was among the most closely-watched in the obesity field this year, with investors driving company shares up on their high expectations for MariTide, or maridebart cafraglutide. Amgens stock fell by double digits in morning trading Tuesday. Bulls will be a little disappointed today, Jefferies analyst Michael Yee wrote in a client note.Dive Insight:Billions of dollars worth of investment have flowed into obesity drug research over the past two years, drawn by the success of Wegovy and Zepbound as well as forecasts that have predicted $100 billion or more in annual sales for obesity and diabetes drugs that target GLP-1.Both Wegovy and Zepbound have already established dominant market positions, though. Ozempic, a diabetes drug that has the same active ingredient as Wegovy and is often prescribed off-label for weight loss, is now consumer shorthand for the new obesity shots.Moreover, Novo and Lilly have data showing Wegovy and Zepbound can help in associated conditions, which have helped expand payer coverage. Wegovy gained FDA approval to reduce the risk of cardiovascular death and complications in people with obesity and established heart disease, which won it limited Medicare coverage. Meanwhile, Zepbound has shown it helps people with obesity who also have sleep apnea or heart failure.Complicating Amgens chances of competing further, both Novo and Lilly have succesor obesity drugs in Phase 3 development that, if successful in the clinic, could reach the market before MariTide.Like dozens of other companies, Amgen is trying to elbow its way in. Similar to Wegovy and Zepbound, MariTide stimulates GLP-1, a gut hormone regulating appetite and satiety. It also acts on a second hormone called GIP, but instead of stimulating it as Zepbound does, MariTide inhibits it.Amgen didnt disclose full details from MariTides Phase 2 trial, which evaluated several doses of the drug, indicating that more would be revealed at future medical meetings and in peer-reviewed journals.The trial enrolled 465 people with obesity or who were overweight, and randomized them to take a placebo, one of four monthly fixed MariTide doses, one eight week fixed dose or one of two escalation regimens up to the maximum dose. It also enrolled 127 people with obesity or who were overweight and also had Type 2 diabetes, which researchers then randomized to take a placebo or monthly fixed-dose arms.Amgen reported weight loss from treatment of up to 20% over 52 weeks for trial participants without diabetes who received MariTide, and up to 17% for those with diabetes. The drug also lowered blood sugar levels for the people with diabetes who took it.Around 11% of people in the dose escalation arms dropped out because of side effects, which is higher than the 7% recorded in Phase 3 trials of Zepbound.Based on the Phase 2 data, MariTides main differentiation appears to be its less frequent dosing, Leerink Partners analyst David Risinger wrote in a note to clients. Yee, meanwhile, wrote that the MariTide is more or less similar to Zepbound on weight loss.Analysts at Piper Sandler took a more positive view of the data, noting that it suggests MariTide appears to match Zepbounds weight loss more quickly.A number of questions remain, but we see a drug that provides equivalent weight loss to tirzepatide much faster ... with monthly dosing ...albeit with a key safety tradeoff, wrote the banks Christopher Raymond in a client note.On Tuesday, Amgen said it would start a Phase 3 clinical program of MariTide, which will include trials in people with obesity and heart disease, sleep apnea, kidney disorders and other conditions related to obesity. '