Amgen reports Phase 2 results for MariTide, a monthly GIP-blocking obesity drug

Amgen on Nov. 26, 2024 released 52-week results from a Phase 2 trial of MariTide (maridebart cafraglutide, formerly AMG 133), an injectable obesity drug given monthly or less often. The company reported average weight loss of up to about 20% at week 52 in people with obesity or overweight who did not have type 2 diabetes, and said it would start a Phase 3 program called MARITIME ^[1].

MariTide works differently from the drugs already on the market. It is an antibody-peptide conjugate that activates the GLP-1 receptor while blocking the GIP receptor ^[1]. Several other experimental drugs, including Eli Lilly's retatrutide, do the opposite and switch the GIP receptor on ^[3]. Amgen says the molecule's long half-life is what allows monthly or less frequent dosing, and that it expects to deliver it in a handheld autoinjector ^[1].

What the trial measured

The study (NCT05669599) enrolled 592 adults in two groups. Cohort A (n=465) had obesity or overweight without type 2 diabetes and was assigned to placebo or monthly fixed doses of 140 mg, 280 mg or 420 mg, an every-8-week 420 mg arm, or one of two dose-escalation arms that stepped up to 420 mg over 4 or 12 weeks. Cohort B (n=127) had type 2 diabetes and received placebo, 140 mg, 280 mg or 420 mg monthly ^[1].

In Cohort B, Amgen reported up to about 17% average weight loss and a drop in average HbA1c of up to 2.2 percentage points at week 52 ^[1]. The company said no weight-loss plateau was seen in either group, which it takes as a sign that more weight loss could follow past 52 weeks ^[1]. It also reported improvements in blood pressure, triglycerides and hs-CRP, and said there was no association between MariTide and bone mineral density changes ^[1].

Side effects were mostly gastrointestinal: nausea, vomiting and constipation. Amgen described nausea and vomiting as mostly mild, transient and tied largely to the first dose, with nausea generally resolving within a median of about six days and vomiting within one to two days. In the dose-escalation arms, roughly 11% of participants stopped because of any adverse event, and fewer than 8% stopped for GI events ^[1].

One caution: the press release gave only "up to ~20%" and "up to ~17%" figures and did not say which statistical analysis produced them, or report placebo-adjusted results ^[1]. That distinction matters. Obesity trials typically report both a treatment-regimen (intention-to-treat) analysis, which counts everyone randomized including people who quit, and an efficacy analysis, which estimates what would have happened if everyone had stayed on the drug. The second number is almost always larger, and company announcements often quote it ^[2].

Why it matters for patients

MariTide is investigational. It is not approved in the United States, and nothing in these results changes what is available at a pharmacy today. As of July 2026, MariTide was still in Phase 3 ^[2].

The potential appeal is scheduling rather than raw weight loss. Current GLP-1 injections are weekly and the newest approved options are daily tablets; a monthly or less frequent shot would mean roughly 12 injections a year instead of 52 ^[1][2]. Whether that convenience translates into better real-world adherence has not been shown.

The trial also tested something most obesity studies do not: how to step down. Part 2 re-randomized participants who had lost at least 15% of body weight to placebo or to 70 mg, 140 mg, 420 mg monthly, or 420 mg every 12 weeks, to look at further weight loss, maintenance on lower or less frequent dosing, and what happens after stopping ^[1]. More than 90% of eligible participants chose to continue ^[1].

What happens next

Amgen said the Phase 2 data would be presented at a medical meeting and submitted for publication ^[1]; the results were later presented at the American Diabetes Association's 85th Scientific Sessions in June 2025 and published in the New England Journal of Medicine ^[3]. The MARITIME Phase 3 program covers obesity and type 2 diabetes, with further studies planned in cardiovascular disease, heart failure and obstructive sleep apnea, and pivotal data expected to read out through 2027 ^[3]. No FDA filing date has been announced in these sources.