Is MariTide a peptide?

Partly. It is an antibody with two GLP-1 agonist peptides conjugated to it, so it is neither a conventional peptide drug nor a small molecule.

Why would blocking GIPR help?

The leading hypothesis is improved tolerability of the co-administered GLP-1 agonist, allowing more GLP-1 signalling before adverse effects limit dosing. This remains a hypothesis.

Is it approved anywhere?

No. It is investigational and holds no marketing authorisation.

What Is Maridebart Cafraglutide (MariTide)?

The short answer

Maridebart cafraglutide, formerly AMG 133 and known as MariTide, is a bispecific molecule: a fully human monoclonal antibody that antagonises the GIP receptor, conjugated through amino-acid linkers to two GLP-1 receptor agonist peptides. It blocks the receptor tirzepatide activates.

Key facts

Former code: AMG 133
Format: Antibody-peptide conjugate (bispecific)
GIPR action: Antagonist (blocking antibody)
GLP-1R action: Agonist (two conjugated peptides)
Antibody type: Fully human monoclonal
First reported: Nature Metabolism 2024 (PMID 38316982)
Phase 2 readout: NEJM, 4 September 2025
Dosing interval: Once monthly
Status: Investigational (no authorisation)

An unusual molecular format

Almost everything else in this field is either a peptide or a small molecule. MariTide is neither: it is a monoclonal antibody with peptides chemically attached. The antibody half blocks the GIP receptor; the two conjugated GLP-1 analogue peptides agonise the GLP-1 receptor. One molecule, two opposite kinds of pharmacology, at two different receptors.

Why build it this way

Antibodies are large and long-lived, with half-lives measured in weeks rather than days, and they are excellent at blocking a receptor with high specificity. Peptides are good agonists but clear quickly. Conjugating them exploits each format for what it does best: antibody for durable antagonism, peptide for agonism, with the antibody's long half-life carrying the whole construct. The practical consequence is dosing intervals longer than weekly.

Research material referenced

Retatrutide 10mg, third-party HPLC tested

Buy Retatrutide · £49.99

What the Phase 1 data reported

The 2024 Nature Metabolism paper described a randomised, double-blind, placebo-controlled Phase 1 study in participants with obesity, reporting an acceptable safety and tolerability profile alongside pronounced dose-dependent weight reduction. Phase 1 is a small, early setting and its purpose is safety and dose-finding rather than establishing efficacy.

The premise it rests on

MariTide exists because a body of evidence suggested blocking GIPR, not activating it, is the useful direction when combined with GLP-1 agonism. That is the direct opposite of tirzepatide's design premise. Both programmes have produced weight reduction, which is the GIP paradox in its sharpest form. Two well-resourced development efforts built on contradictory readings of the same receptor, neither obviously wrong.

What is not yet known

Whether the reduction is durable, how it compares head-to-head against approved dual agonists, and whether the tolerability advantage the antagonist premise predicts actually materialises at scale. It holds no marketing authorisation in any jurisdiction and is not available outside clinical trials.

The Phase 2 readout

Jastreboff and colleagues published the Phase 2 trial in the New England Journal of Medicine on 4 September 2025, under the title once-monthly maridebart cafraglutide for the treatment of obesity. The dosing interval is the detail worth holding onto: monthly rather than weekly, which follows from the format. An antibody circulates for weeks because it is large enough to escape renal filtration and is recycled by the neonatal Fc receptor, so conjugating GLP-1 peptides to one gives them the antibody’s persistence rather than their own.

Frequently asked questions

Is MariTide a peptide?: Partly. It is an antibody with two GLP-1 agonist peptides conjugated to it, so it is neither a conventional peptide drug nor a small molecule.
Why would blocking GIPR help?: The leading hypothesis is improved tolerability of the co-administered GLP-1 agonist, allowing more GLP-1 signalling before adverse effects limit dosing. This remains a hypothesis.
Is it approved anywhere?: No. It is investigational and holds no marketing authorisation.

Extended research context

The GLP-1 & Incretin Science deep dive

Deep dive: the two routes to a bigger effect

Every compound trying to beat GLP-1 alone has taken one of two routes. The first adds more receptors from the same hormone family: GIP in tirzepatide, GIP and glucagon in retatrutide. The second adds a non-incretin satiety hormone, which in practice means amylin: CagriSema combines cagrilintide with semaglutide, and amycretin engages both receptors from one molecule. Both routes work, because they recruit signalling pathways that do not fully overlap. Neither has escaped the constraint that binds all of them, which is that gastrointestinal tolerability worsens as effect size grows.

Deep dive: why a percentage is not a result

The most-quoted numbers in this field are the least comparable. REDEFINE 1 reported 22.7% and 20.4% for the same compound in the same trial, the first among participants who adhered to treatment, the second across everyone randomised. TRIUMPH-1 reported 28.3% in an uncomplicated obesity population while TRIUMPH-3 reported up to 22.6% in adults with established cardiovascular disease, using the same compound. Before any two figures can be compared they have to match on estimand, population, duration, comparator and whether the number is placebo-adjusted. Most published comparisons match on none of them.

Deep dive: what happens after the trial stops

Every headline figure describes weight while treatment continues. The STEP-1 extension found that a year after semaglutide was stopped, participants had given back roughly two-thirds of what they lost, moving from 17.3% mean reduction to a net 5.6%, though average weight remained below baseline and nearly half stayed at least 5% down. Meta-analysis puts regain at around 0.8 kg per month. This is why maintenance studies such as TRIUMPH-6 matter more to the field's future than another two points of peak reduction.

Research applications

▸Comparing incretin and amylin compounds on a like-for-like basis
▸Interpreting estimands, thresholds and placebo-adjusted figures in trial reports
▸Tracking the obesity pipeline across sponsors and jurisdictions
▸Understanding receptor pharmacology behind GLP-1, GIP, glucagon and amylin
▸Distinguishing licensed medicines from investigational compounds

Handling checklist

✓Identify which estimand a quoted percentage comes from before citing it
✓Check the trial population and baseline BMI against the comparison you are making
✓Confirm the duration and whether the reduction curve had plateaued
✓Read discontinuation rates alongside efficacy figures
✓Verify every NCT identifier against ClinicalTrials.gov rather than secondary reporting

Common research-handling mistakes

Learnt from thousands of researcher orders across our UK labs.

✗ Comparing headline percentages across different trials

Fix: Population, duration, estimand and comparator all differ; the numbers are not interchangeable.

✗ Quoting the larger of two figures from the same trial

Fix: Name the estimand. Efficacy and treatment-policy answer different questions.

✗ Treating peak reduction as a durable outcome

Fix: Substantial regain follows cessation across the class; peak figures describe a maintained state.

✗ Assuming an oral route means a weaker mechanism

Fix: Route and receptor count are independent. Orforglipron is weaker because it hits one receptor, not because it is a tablet.

✗ Reading investigational compounds as available treatments

Fix: Most of this pipeline holds no authorisation anywhere; mazdutide is approved only in China.

Continue researching

Peer-reviewed guides, comparators and matched reference materials.

Primary sources & clinical trials

Peer-reviewed research and registered trials from PubMed, ClinicalTrials.gov, PubChem, FDA and NIH. All links open in a new tab and point to the primary source, so every claim can be verified at origin.

UKP

Written and reviewed by

The UK Peptides Editorial Team · Research library, UK Peptides

The editorial team is responsible for supplier selection, batch release decisions and the content published in this research library. Every article here is sourced to primary literature and every product page to a signed third-party certificate. Corrections are made in place and the review date updated.

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What Is Maridebart Cafraglutide? Antibody Meets Peptide