MariTide in 2026: What Monthly Peptide–Antibody Conjugation Could Change in Obesity Research

Evidence status: Maridebart cafraglutide (MariTide; formerly AMG 133) is an investigational peptide–antibody conjugate being studied for obesity, overweight and related cardiometabolic conditions. It is not FDA-approved. The strongest efficacy evidence currently available is a randomized Phase 2 trial published in The New England Journal of Medicine; longer-term maintenance findings described below are sponsor-reported topline data and should be treated as preliminary until fully peer reviewed.

Why MariTide is scientifically interesting

Most of the recent metabolic-drug conversation has centered on weekly incretin agonists. MariTide explores a different engineering strategy: a long-acting conjugate that combines GLP-1 receptor agonism with GIP receptor antagonism. The antibody-based architecture is intended to extend exposure enough to support monthly or potentially less-frequent administration.

That makes MariTide scientifically valuable for reasons beyond a simple comparison of weight-loss percentages. It tests whether a peptide-based metabolic signal can be paired with an antibody scaffold to change pharmacokinetics, dosing frequency and potentially long-term maintenance behavior. Those questions are now being examined across a broad Phase 3 program.

Peer-reviewed Phase 2 evidence

The pivotal published Phase 2 study enrolled 592 adults with overweight or obesity, including a cohort with type 2 diabetes. It was randomized, double-blind, placebo-controlled and dose-ranging. At 52 weeks, the treatment-policy estimand showed mean body-weight changes ranging from −12.3% to −16.2% in participants without diabetes receiving MariTide, versus −2.5% with placebo. In the cohort with type 2 diabetes, mean changes ranged from −8.4% to −12.3%, versus −1.7% with placebo. The diabetes cohort also showed mean HbA1c reductions of approximately 1.2 to 1.6 percentage points across MariTide groups, compared with a slight increase with placebo.

The trial also matters because it did not report an obvious weight-loss plateau by week 52. That observation is intriguing, but it should not be interpreted as proof that weight loss would continue indefinitely. The Phase 2 duration and design cannot answer that question.

Gastrointestinal adverse events were common, consistent with the broader GLP-1 therapeutic class. Importantly, the published study found that gastrointestinal events were less frequent with dose escalation and a lower starting dose. No unexpected safety signal emerged in the Phase 2 report. These are study-protocol observations, not instructions for use or self-administration.

What changed after the first 52 weeks?

Sponsor-reported topline data: Amgen reported in February 2026 that the exploratory second year of the Phase 2 program had been completed in participants who had lost at least 15% of body weight during the first 52 weeks and entered the extension. According to the company, the large majority maintained the weight loss achieved during year one for another 52 weeks while receiving a lower monthly dose or quarterly administration. Amgen also reported a very low incidence of nausea and vomiting during the second year, no new safety signals, and sustained cardiometabolic improvements.

Those findings are potentially important because long-term maintenance is one of the central unresolved questions in obesity pharmacotherapy. However, they are not equivalent to the peer-reviewed first-year evidence. The extension selected participants who had already achieved substantial weight loss and remained eligible to continue, which can enrich the population for responders and tolerators. Detailed numerical results and a peer-reviewed publication will be needed before the magnitude and generalizability of the maintenance effect can be judged confidently.

The Phase 3 MARITIME program is testing more than weight loss

As of 2026, Amgen reports that MARITIME-1 and MARITIME-2 are ongoing Phase 3 chronic-weight-management studies in adults without and with type 2 diabetes, respectively. The development program has expanded into cardiovascular outcomes, heart failure and obstructive sleep apnea. Additional studies are examining long-term maintenance and switching from weekly semaglutide or tirzepatide to less-frequent MariTide schedules. Amgen also reported in 2026 that a Phase 2b study is enrolling participants with elevated liver fat.

This breadth is significant. A successful obesity program ultimately has to establish more than scale weight reduction. Cardiovascular events, heart-failure outcomes, sleep-apnea measures, glycemic control, body composition, liver biology, tolerability, adherence and durability can all affect the real clinical value of a metabolic therapy. The MARITIME program is designed to address several of those questions, but many answers remain pending.

A useful lesson in peptide engineering

MariTide illustrates an increasingly important direction in peptide science: pharmacology can be changed not only by modifying the peptide sequence, but also by changing the molecular platform that carries or presents it. Conjugation to a large biologic scaffold can substantially alter circulation time and exposure. In principle, that may allow researchers to separate the frequency of administration from the short natural half-lives that characterize many endogenous peptide signals.

That concept has broader implications for peptide drug development. Long-acting conjugates could eventually be explored wherever a peptide pathway has attractive biology but inconvenient pharmacokinetics. MariTide is therefore useful to watch even if its eventual efficacy, safety or commercial profile differs from current expectations.

Important limitations

• MariTide remains investigational and is not FDA-approved.
• The strongest published efficacy evidence is Phase 2; Phase 3 outcome data are still needed.
• Gastrointestinal adverse events were common in the Phase 2 program.
• The sponsor-reported second-year maintenance findings have not yet been given the same evidentiary weight as a full peer-reviewed publication.
• The extension population was selected from participants who had already achieved substantial first-year weight loss, limiting direct generalization to all patients.
• Weight reduction alone cannot establish cardiovascular, heart-failure, sleep-apnea or liver-outcome benefit; those questions require their dedicated trials.
• Less-frequent administration is scientifically attractive, but whether it meaningfully improves long-term adherence or outcomes remains to be demonstrated.

Bottom line

MariTide is one of the more distinctive late-stage metabolic peptide programs because it combines dual-pathway pharmacology with peptide–antibody conjugation and unusually infrequent administration. The peer-reviewed Phase 2 results support a genuine efficacy signal in obesity with and without type 2 diabetes, while also showing the gastrointestinal tolerability challenges familiar to incretin-based therapy. Sponsor-reported second-year findings raise an especially interesting possibility: substantial weight loss may be maintainable with less-frequent exposure in selected responders. That is promising, but still preliminary.

The most consequential evidence will come from Phase 3. If the MARITIME studies confirm durable efficacy, acceptable safety and meaningful benefits across obesity-related conditions, MariTide could help establish long-acting peptide–antibody conjugation as a broader platform in metabolic medicine. Until those results arrive, the appropriate conclusion is one of scientific promise rather than clinical certainty.

Sources

• Jastreboff AM, et al. Once-Monthly Maridebart Cafraglutide for the Treatment of Obesity — A Phase 2 Trial. New England Journal of Medicine. 2025.
• ClinicalTrials.gov NCT05669599 — Phase 2 dose-ranging study of maridebart cafraglutide.
• Amgen, February 2026 — Phase 2 extension topline findings and MARITIME program update. Commercial sponsor source; topline findings are clearly treated as preliminary in this article.
• Amgen, August 2026 — current MARITIME Phase 3 and liver-fat program status. Commercial sponsor source.

Commercial disclosure: MariTide is developed by Amgen, which sponsored the Phase 2 study and the ongoing development program. Sponsor statements are used here to describe trial status and clearly labeled topline findings; scientific conclusions are based preferentially on peer-reviewed evidence and registered-trial information. LoCo Research Journal is not presenting this article as medical advice, a dosing guide or a recommendation to use an investigational compound.