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MariTide (Maridebart Cafraglutide): A Research Guide to Amgen’s Monthly GLP-1 Agonist / GIP Antagonist

Short answer: MariTide (maridebart cafraglutide, code AMG 133) is Amgen’s investigational obesity drug — a peptide–antibody conjugate that agonises the GLP-1 receptor and antagonises the GIP receptor, with a ~21-day half-life supporting once-monthly subcutaneous dosing. Phase 2 (NEJM, 2025) reported mean weight loss of up to ~20% at 52 weeks in obesity without diabetes, with no plateau. It is in the Phase 3 MARITIME programme and has no marketing authorisation anywhere in the world . MariTide is a proprietary conjugate, not a reference peptide — New-U does not sell it. Part of our next obesity-research wave overview.

Plain-English summary. MariTide is an unapproved investigational drug. The FDA, MHRA and EMA have not authorised it. It is also structurally a biologic (an antibody conjugate), not a simple peptide that research-compound suppliers stock. This page is general information, not legal or medical advice; do not use unapproved compounds on people.

What MariTide actually is

Most obesity drugs are peptides. MariTide is not — it is a peptide–antibody conjugate : a monoclonal-antibody scaffold with GLP-1 analogue peptides chemically attached. That architecture is the whole point. Antibodies circulate for weeks, so bolting the active peptides onto an antibody backbone stretches the half-life to roughly 21 days — about three times semaglutide’s ~7 days — which is what makes once-monthly (and potentially less-frequent) dosing realistic.

Its developmental code was AMG 133 ; the generic name is maridebart cafraglutide . The molecular and pharmacology detail is indexed under PubMed: maridebart cafraglutide.

The GIP paradox: agonise GLP-1, block GIP

Here is the genuinely counter-intuitive part. Tirzepatide, the most successful incretin drug to date, activates the GIP receptor. MariTide does the opposite — it blocks it — while still agonising GLP-1. And yet both produce major weight loss. How can activating and blocking the same receptor both work?

GLP-1 receptor agonism — the shared engine: slows gastric emptying, suppresses appetite centrally, improves glucose-dependent insulin secretion.

GIP receptor antagonism — the differentiator. The leading hypotheses are that chronic GIP agonism ends up desensitising the receptor (so an agonist and an antagonist converge on a similar downstream state), and that central versus peripheral GIP signalling pull in different directions. The honest answer is that the field has not settled this; it is an active research question.

For the contrasting GIP- agonist design, see our tirzepatide research guide.

The Phase 2 evidence

The Phase 2 trial was published in the New England Journal of Medicine in 2025 and presented at the American Diabetes Association’s 85th Scientific Sessions. Headline findings over 52 weeks:

Population Mean weight change at 52 weeks Notable Obesity, without type-2 diabetes up to ~−20% No plateau by week 52 Obesity, with type-2 diabetes up to ~−17% HbA1c reduced up to ~2.2%

Beyond weight, the trial reported improvements across pre-specified cardiometabolic measures — waist circumference, blood pressure, high-sensitivity C-reactive protein (hs-CRP) and selected lipids. The fact that the weight curve had not flattened at 52 weeks is one reason the Phase 3 readouts are closely watched.

Phase 3: the MARITIME programme

MariTide has advanced into the MARITIME Phase 3 programme — 72-week studies evaluating efficacy, safety and tolerability in people with obesity or overweight, with and without type-2 diabetes. Topline timing and any regulatory submission schedule are subject to change; refer to Amgen investor disclosures for the current position. Registered studies are listed on ClinicalTrials.gov.

How MariTide compares

Compound Receptor profile Format Cadence Status MariTide GLP-1 agonist + GIP antagonist Peptide–antibody conjugate ~Monthly Phase 3, no approval Tirzepatide GLP-1 + GIP agonist Peptide Weekly Approved Retatrutide GLP-1 + GIP + glucagon agonist Peptide Weekly Phase 3, no approval Semaglutide GLP-1 agonist Peptide Weekly Approved

MariTide’s distinctive selling points are the monthly cadence and the GIP-antagonist mechanism — both unusual in a field otherwise converging on weekly GIP agonists.

MariTide and research compounds

Because MariTide is an antibody conjugate rather than a short synthetic peptide, it sits outside what research-compound suppliers can characterise and verify by HPLC and mass spec. New-U does not sell MariTide , and any listing claiming to is selling something it cannot authenticate. The lawful, verifiable research references in the same therapeutic area are the established GLP-1-class peptides:

Semaglutide — the GLP-1 single-agonist reference.

Tirzepatide — the GLP-1 / GIP dual-agonist reference.

Retatrutide — the triple-agonist reference.

Each ships as a sealed, lyophilised reference peptide, with the per-batch Certificate of Analysis published online, verified to >99% HPLC purity, research use only .

Red flags on MariTide listings

Because there is no licensed MariTide product anywhere, treat any “buy MariTide” listing with maximum caution. Walk away if it:

Calls itself a “pharmacy” or “clinic” supplier of MariTide — no such supplier exists; it is not a medicine.

Quotes dosing schedules or weight-loss promises — that re-characterises it as an unlicensed medicine.

Claims to sell the antibody conjugate as a reference reagent — that is not a product a CoA can verify the way a short peptide can.

Has no batch-specific CoA, sells “ready-to-inject” pens, or operates Telegram-only with no legal entity.

Frequently Asked Questions

What is MariTide? Amgen’s investigational obesity drug maridebart cafraglutide (AMG 133) — a peptide–antibody conjugate that agonises GLP-1 and antagonises GIP, dosed about once a month.

Is MariTide approved? No. As of mid-2026 it has no marketing authorisation anywhere; it is in the Phase 3 MARITIME programme.

How much weight loss did it show? Up to ~20% mean over 52 weeks in obesity without diabetes (Phase 2, NEJM 2025), without a plateau.

Why block GIP when tirzepatide activates it? An open question — likely receptor desensitisation and central-vs-peripheral GIP signalling. Both designs produce weight loss; the mechanism is unsettled.

Can I buy MariTide as a research compound? No — it is a proprietary antibody conjugate, not a verifiable reference peptide. New-U catalogues the established GLP-1-class references instead.

Primary sources & further reading

New England Journal of Medicine — Once-Monthly Maridebart Cafraglutide for Obesity — A Phase 2 Trial (2025)

Amgen — Phase 2 obesity results, ADA 2025

U.S. National Library of Medicine — PubMed: maridebart cafraglutide

ClinicalTrials.gov — MARITIME programme

U.S. FDA — FDA (no MariTide approval as of publication)

External links are provided for research reference only; New-U is not affiliated with the cited organisations and links carry no endorsement either way.

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Lab-Verified GLP-1-Class Research References

New-U Research Compounds catalogues semaglutide, tirzepatide and retatrutide as sealed 10-vial packs of lyophilised reference peptide, independently verified by Janoshik and Freedom Diagnostics for >99% HPLC purity, with the per-batch Certificate of Analysis published online. Research use only - all claims made on this site are for testing and research use only.

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