Maridebart Cafraglutide

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Overview

Maridebart cafraglutide — known as MariTide, and previously by the code AMG 133 — is the most structurally unusual drug in the obesity pipeline. It is a peptide-antibody conjugate: two GLP-1 analog peptides chemically attached to a monoclonal antibody that blocks the GIP receptor. It is simultaneously a peptide drug and a biologic.

Two things make it distinctive

The first is dosing frequency. Antibodies persist in the body for weeks, and conjugating the peptides to one drags their duration along with it. MariTide is being studied at monthly or less frequent intervals, against weekly for essentially every competing incretin drug. For a chronic therapy people are expected to take indefinitely, twelve injections a year instead of fifty-two is a real difference.

The second is the mechanism, which runs against the grain of the field. MariTide activates GLP-1 receptors while blocking GIP receptors. Tirzepatide, the current market leader, activates both. Two drugs doing opposite things at the same receptor while both producing substantial weight loss is one of the genuine open puzzles in metabolic pharmacology.

Status

MariTide is developed by Amgen and is investigational, not approved. Phase 2 is complete, including an extension phase, and the Phase 3 MARITIME program is under way across obesity, type 2 diabetes, cardiovascular outcomes, heart failure, and obstructive sleep apnea.

How it works

The two halves of the molecule

• The peptide half consists of GLP-1 receptor agonist peptides that reduce appetite, slow gastric emptying, and improve glucose-dependent insulin secretion — the familiar incretin mechanism.
• The antibody half is a monoclonal antibody that binds the GIP receptor and blocks it, preventing GIP from signaling.

The GIP paradox

GIP is an incretin hormone, and there are credible arguments for both activating and blocking its receptor for weight loss. Agonism may enhance the effects of GLP-1 signaling centrally and improve tolerability, which is the tirzepatide story. Antagonism may counter GIP's role in promoting fat storage in adipose tissue, which is the MariTide story. A further possibility is that sustained GIP agonism ultimately desensitizes the receptor, meaning agonists and antagonists converge on a similar end state by different routes. This is unresolved, and the fact that drugs on both sides work is why it remains interesting rather than settled.

Why the antibody backbone matters

Beyond providing the GIP-blocking function, the antibody gives the molecule the long circulating half-life that monthly dosing depends on. The conjugate format is what makes the whole design possible, and it is a notable piece of protein engineering regardless of where the drug ends up commercially.

Clinical evidence

Phase 2 results

In the Phase 2 chronic weight management study, once-monthly maridebart cafraglutide produced weight loss of up to roughly 20% at about a year, with the curve not clearly flattening by the end of the treatment period — meaning more weight loss might have continued with longer dosing. Substantial weight loss was also seen in participants with type 2 diabetes, though as with the entire drug class the magnitude was smaller than in those without diabetes.

The extension phase

Part 2 of the Phase 2 study followed participants for an additional 52 weeks and reported that weight loss was maintained, with tolerability described as good and cardiometabolic improvements sustained. Maintenance data matter disproportionately in obesity medicine, where weight regain after stopping treatment is the norm, and where the practical question is not how much weight comes off but whether it stays off.

The MARITIME Phase 3 program

Amgen has taken MariTide into a broad Phase 3 program: MARITIME-1 and MARITIME-2 in chronic weight management without and with type 2 diabetes, MARITIME-CV for cardiovascular outcomes, MARITIME-HF in heart failure with preserved or mildly reduced ejection fraction, and MARITIME-OSA-1 and -2 in obstructive sleep apnea. The breadth signals that Amgen is pursuing the cardiometabolic-outcomes positioning that has become the competitive battleground in this class, not weight loss alone.

Evidence tier

Phase 2 with extension data — real randomized human evidence, but mid-stage. Phase 3 results are not yet available and no regulator has reviewed the drug.

Safety & status

Reported effects

Adverse events have been predominantly gastrointestinal — nausea and vomiting most prominently — consistent with GLP-1-based therapy. Early studies saw a meaningful rate of these events after the first doses, and dose-escalation strategies were introduced to improve tolerability.

Monthly dosing introduces a consideration that weekly drugs do not have: if a dose is poorly tolerated, the exposure cannot be withdrawn quickly. A long half-life is an advantage for convenience and a constraint for managing side effects, and how that balance plays out at scale is one of the things Phase 3 exists to determine.

The broader class considerations for GLP-1 therapies apply, and questions specific to chronic GIP receptor blockade — a mechanism with no long-term human precedent — remain genuinely open.

Status

MariTide is not FDA-approved and is available only through clinical trials. It is not obtainable by prescription or from any legitimate commercial source. Because it is an antibody conjugate rather than a simple peptide, claims by grey-market vendors to supply it are especially implausible — this is a complex biologic, not something reproduced in an unregulated peptide facility.

For the contrasting approach at the GIP receptor, see tirzepatide.

Frequently asked questions

References

Each source links to its original record — peer-reviewed studies, regulator pages, or reference texts, labelled by type. We summarize findings neutrally; a citation is a reference, not an endorsement, and not a claim that its authors reviewed this page.

1. Jastreboff AM, Ryan DH, Bays HE, et al. Once-Monthly Maridebart Cafraglutide for the Treatment of Obesity - A Phase 2 Trial. N Engl J Med. 2025. Peer-reviewed study
2. Véniant MM, Lu SC, Atangan L, et al. A GIPR antagonist conjugated to GLP-1 analogues promotes weight loss with improved metabolic parameters in preclinical and phase 1 settings. Nat Metab. 2024. Peer-reviewed study
3. Véniant MM, Lu SC, Atangan L, et al.. A GIPR antagonist conjugated to GLP-1 analogues promotes weight loss with improved metabolic parameters in preclinical and phase 1 settings. Nat Metab. 2024. Peer-reviewed study
4. Jastreboff AM, Ryan DH, Bays HE, et al.. Once-Monthly Maridebart Cafraglutide for the Treatment of Obesity - A Phase 2 Trial. N Engl J Med. 2025. Peer-reviewed study
5. Greenhill C. Phase I results for AMG 133. Nat Rev Endocrinol. 2024. Peer-reviewed study
6. Douros JD, Mowery SA, Knerr PJ. The Premise of the Paradox: Examining the Evidence That Motivated GIPR Agonist and Antagonist Drug Development Programs. J Clin Med. 2025. Peer-reviewed study