Amgen starts a phase 3 switch study for monthly MariTide

Amgen started a phase 3 study in May 2026 that enrolls patients already on weekly GLP-1 therapies and switches them to MariTide, a monthly injectable, according to the development description. The company's pitch is straightforward: MariTide needs one shot a month instead of one a week, which it is framing as its main edge over semaglutide (Ozempic, Wegovy, Rybelsus) and tirzepatide (Mounjaro, Zepbound) ^[1].

MariTide is a GLP-1/GIP combination drug, and it is already in a broader phase 3 program called MARITIME that runs 72 weeks and covers obesity, type 2 diabetes, cardiovascular disease, heart failure, and obstructive sleep apnea ^[1]. In earlier phase 2 testing, MariTide produced weight loss up to roughly 20% over 52 weeks under the analysis that assumes patients stayed on treatment throughout, and 12.3% to 16.2% under an analysis that counts everyone as randomized, including people who stopped ^[1]. Neither of these numbers is what any individual patient would necessarily see, and they are trial results, not label claims.

Amgen is one of the larger, profitable companies chasing this market, with a market capitalization of about $191.7 billion as tracked by one industry data source ^[1]. But it trails Eli Lilly and Novo Nordisk in obesity drug leadership, and a gastrointestinal tolerability question remains open for MariTide ^[1]. In August 2026, Amgen also discontinued an undisclosed early-stage obesity candidate that had been in phase 1, a move one tracker described as concentrating the company's obesity strategy on MariTide alone ^[1].

The sources provided do not give specifics on how many patients are enrolled in the switch study, what weekly drugs participants are coming off of, or when results are expected. That level of detail is not yet known from what is available here.

Why it matters for patients

Dosing frequency is a real practical difference for people on GLP-1 drugs. Weekly injections are already less demanding than daily pills, and a monthly shot would cut the number of injections further, from about 52 a year down to 12. For patients who find weekly dosing burdensome, or who worry about missed doses, that could matter.

But a switch study answering whether patients can move from a weekly drug to MariTide without losing efficacy or gaining new side effects is different from a study proving MariTide works as well as semaglutide or tirzepatide in people starting fresh. The sources do not report head-to-head efficacy or side-effect comparisons between MariTide and the approved weekly drugs. Until that data exists, it is not known whether the convenience of monthly dosing would come with a tradeoff in weight loss, side effects, or something else.

MariTide is not approved by the FDA. It remains in clinical trials, and nothing here should be read as information about its safety or effectiveness in the way an approved label would provide.

What happens next

Amgen's broader MARITIME phase 3 program is a 72-week trial testing MariTide across obesity, type 2 diabetes, cardiovascular disease, heart failure, and sleep apnea, though a specific completion date is not given in the source material ^[1]. No date for results from the newly started switch study appears in the available sources. Meanwhile, competitors are moving on separate timelines: Eli Lilly's retatrutide, a triple agonist, reported phase 3 topline results in some trials with weight loss reaching 25% to 28.3% depending on the analysis, and Novo Nordisk's CagriSema is awaiting an FDA decision after being filed with the agency [1, 2]. How MariTide's monthly-dosing pitch stacks up against those rivals is something patients and clinicians will only be able to judge once more trial data, including from the new switch study, becomes public.