MariTide is the working name for maridebart cafraglutide, Amgen's investigational obesity treatment and one of the more structurally unusual candidates in the current wave of peptide drug development. Instead of a once-weekly injection like semaglutide or tirzepatide, MariTide is designed for once-monthly dosing, built around a mechanism that takes an opposite approach to GIP than tirzepatide does.
What It Is
MariTide (Amgen's internal code name is AMG 133) is not a simple peptide injection; it's an antibody-peptide conjugate. The molecule attaches GLP-1 receptor-agonist peptide fragments to a human IgG2 antibody backbone that itself blocks, or antagonizes, the GIP receptor. That combination — GIP antagonism paired with GLP-1 agonism — is a deliberate departure from tirzepatide, which activates both the GIP and GLP-1 receptors. Researchers have proposed a few explanations for why blocking GIP might produce similar or complementary effects to activating it, including effects on fat cell metabolism, but the exact mechanism by which GIP antagonism contributes to weight loss is still an active area of research rather than settled science.
The antibody component is also what enables monthly dosing: antibodies naturally have a much longer half-life in the body than small peptides alone, so attaching the GLP-1 peptides to this larger antibody scaffold slows their clearance substantially compared with a standalone peptide drug.
What the Research Shows
MariTide's human evidence so far comes primarily from a Phase 2 trial involving 592 adults. Among participants without diabetes, the trial reported 12% to 16% placebo-subtracted weight loss at 52 weeks, depending on dose. Among participants with both obesity and type 2 diabetes, weight loss above placebo ran lower, in the roughly 8% to 12% range, alongside HbA1c improvements of 1.2 to 1.6 percentage points — a pattern similar to what's seen with other GLP-1-class drugs, where diabetes tends to modestly blunt the weight-loss response compared with non-diabetic participants. Phase 1 data reported no treatment-related serious adverse events or discontinuations, and the larger Phase 2 program found a side-effect profile dominated by the gastrointestinal symptoms — nausea, vomiting, and constipation — typical of this drug class.
It's worth being clear about the limits of this evidence: Phase 2 trials are designed primarily to establish dosing and signal efficacy in a few hundred people, not to generate the kind of large-scale, long-duration safety data that comes from Phase 3 programs enrolling thousands of participants over a year or more. Amgen has moved MariTide into Phase 3 testing, under the MARITIME trial program that began in 2024 and 2025, which will be the data that most directly informs any future regulatory decision.
Regulatory Status
MariTide is not FDA-approved for any use. It is strictly an investigational drug, available only to people enrolled in its clinical trials, and it is not legal or appropriate to source outside that context. Amgen has not publicly committed to a specific FDA filing date, and outside analysts have generally characterized an approval before 2028 as an optimistic timeline given where the Phase 3 program currently stands.
How It Fits Among Obesity Drugs in Development
MariTide sits alongside a growing list of next-generation candidates — including triple agonists like retatrutide and other long-acting GLP-1 designs — all competing to improve on the weekly-injection, GLP-1-centric model set by semaglutide and tirzepatide. Monthly dosing, if MariTide's Phase 3 results hold up and the drug is eventually approved, would be a genuine convenience advantage for patients who currently manage weekly injections, but it will need to demonstrate an efficacy and safety profile that's at least competitive with already-approved weekly options to find a place in a crowded market. Anyone weighing current treatment options should discuss what's actually FDA-approved and available today with their physician rather than anticipating results from drugs still in trials.