Why does MariTide block GIP while tirzepatide activates it?

Human genetics data supports both approaches paradoxically. Loss-of-function GIPR variants correlate with lower BMI, suggesting GIPR antagonism should promote weight loss. Yet tirzepatide's GIP agonism also produces dramatic weight loss. The field's working explanation involves receptor desensitization: chronic GIP agonism may functionally mimic antagonism through downregulation. MariTide tests pharmacologic antagonism directly. Both mechanisms appear to work, which is unusual but well-documented.

How does monthly dosing change the patient experience?

Practically, it means 12 injections per year instead of 52. For patients who find weekly injections burdensome — or who forget doses — monthly administration could meaningfully improve adherence. The long half-life also means the 'washout' after stopping is slower: Phase 1 showed weight loss maintained up to 150 days post-treatment. This could reduce the dramatic rebound weight gain seen when weekly GLP-1s are discontinued.

How does MariTide compare to tirzepatide?

Both are dual-mechanism obesity drugs. Tirzepatide: weekly SC injection, GLP-1+GIP co-agonist, ~20.2% weight loss at 72 weeks (SURMOUNT-1). MariTide: monthly SC injection, GLP-1 agonist + GIP antagonist, ~16-21.6% at 52 weeks with curves still declining. Cross-trial comparisons are not head-to-head, but MariTide's monthly dosing and trajectory-without-plateau position it as a credible competitor.

MariTide

Amgen's first-in-class once-monthly bispecific antibody-peptide conjugate for obesity — GLP-1 receptor agonist + GIP receptor antagonist. Phase 2 NEJM showed up to 21.6% weight loss at 52 weeks with no plateau.

ModerateLimited Data

What is MariTide?

MariTide (maridebart cafraglutide, AMG 133) is Amgen's first-in-class bispecific antibody-peptide conjugate for obesity. It combines a fully human anti-GIPR monoclonal antagonist antibody with two GLP-1 agonist peptide arms — creating a single molecule that activates the GLP-1 receptor while simultaneously blocking the GIP receptor. This is the opposite direction from tirzepatide (which agonizes both), based on human genetics data showing loss-of-function GIPR variants are associated with lower BMI. The antibody scaffold gives MariTide a remarkable ~21-day half-life, enabling once-monthly (Q4W) or even Q8W subcutaneous dosing — approximately 12 injections per year vs. 52 for weekly agents. Phase 2 NEJM (Sept 2025, 592 participants, 52 weeks): up to 16.2% weight loss (treatment-policy estimand) with topline reports noting ~21.6% at the top dose. Weight loss was maintained up to 150 days post-treatment in Phase 1. Phase 3 MARITIME program (4,500+ participants) launched March 2025, with MARITIME-1 readout expected early 2027.

Why People Talk About It

Once-monthly dosing (vs weekly for other incretins)

Moderate

Weight loss rivaling tirzepatide with less frequent dosing

Moderate

Novel GIPR antagonism hypothesis (opposite of tirzepatide)

Moderate

Prolonged post-treatment effect (weight maintained up to 150 days after last dose in Phase 1)

Preliminary

Type 2 diabetes control (HbA1c -1.2 to -1.6 in Phase 2)

Moderate

How It Works

MariTide is a molecular hybrid — part antibody, part peptide. The antibody part blocks the GIP receptor, and two peptide arms activate the GLP-1 receptor. The antibody gives MariTide an extremely long half-life (about 3 weeks), which is why it only needs to be injected once a month instead of weekly like Ozempic or Zepbound. When you stop, it slowly washes out over several months, which may soften the dramatic weight regain that happens after stopping weekly GLP-1s.

Common Questions

Safety Information

Important Safety Notes

Common Side Effects

Nausea (most common, predominantly after first dose)VomitingConstipationMostly mild, transientDose escalation significantly reduced GI AEs

Cautions

• Not FDA-approved — investigational drug in Phase 3
• 11% discontinuation due to AEs in dose-escalation arms
• GI side effects may be harder to manage given monthly dosing (cannot quickly adjust dose)
• Long half-life (~21 days) means drug persists weeks after discontinuation

What We Don't Know

Cardiovascular outcomes data pending from MARITIME-CV. Long-term safety beyond 52 weeks not yet established. Real-world tolerability of monthly dosing vs weekly (where dose adjustment is quicker) is untested. Immunogenicity concerns inherent to antibody-peptide conjugates require longer-term monitoring.

Published Research

8 studies

Obesity pharmacotherapy reimagined: The era of multi-receptor agonists and next-generation metabolic modulators.

ReviewPMID: 41948476

A metabolic comparison of GIPR agonism versus GIPR antagonism in male mice.

PreclinicalPMID: 41287212

Novel GLP-1-based Medications for Type 2 Diabetes and Obesity.

ReviewPMID: 41054801

Once-Monthly Maridebart Cafraglutide for the Treatment of Obesity — A Phase 2 Trial.

Phase 2, 592 participants, 52 weeks — up to 16.2% weight loss (treatment-policy), ~21.6% (efficacy estimand)

Randomized Controlled TrialPMID: 40549887

The Premise of the Paradox: Examining the Evidence That Motivated GIPR Agonist and Antagonist Drug Development Programs.

ReviewPMID: 40507574

Characterization of genetic variants of GIPR reveals a contribution of β-arrestin to metabolic phenotypes.

PreclinicalPMID: 38871982

A GIPR antagonist conjugated to GLP-1 analogues promotes weight loss with improved metabolic parameters in preclinical and phase 1 settings.

Preclinical/Phase 1PMID: 38316982

Beyond the pancreas: contrasting cardiometabolic actions of GIP and GLP1.

ReviewPMID: 36509857

Mechanism of Action

MariTide (maridebart cafraglutide) is a bispecific antibody-peptide conjugate combining one fully human anti-GIPR monoclonal antagonist antibody (the 'cafraglutide' scaffold) with two GLP-1 agonist peptide arms (the 'maridebart' moieties) attached via amino acid linkers. GLP-1R agonism drives appetite suppression, slowed gastric emptying, and glucose-dependent insulin secretion. GIPR antagonism targets the paradoxical human genetics signal (loss-of-function GIPR variants → lower BMI). The antibody scaffold confers ~21-day half-life (vs semaglutide ~1 week, tirzepatide ~5 days), enabling once-monthly or even Q8W dosing. Phase 2 (NCT05669599, 592 participants, 52 weeks, NEJM 2025): obesity cohort weight loss −12.3% to −16.2% (treatment-policy estimand), up to ~21.6% efficacy estimand; obesity+T2D cohort −8.4% to −12.3% with HbA1c reductions of −1.2 to −1.6 percentage points. No weight-loss plateau observed at 52 weeks. Dose escalation (4-week or 12-week) substantially reduced GI AEs. Phase 1 showed weight loss maintained up to 150 days post-last-dose.

Evidence Snapshot

Overall Confidence60%

Human Clinical Evidence

Moderate. Phase 1 (NCT04478708, Nature Metabolism 2024, PMID: 38316982): dose-dependent weight loss, weight maintained up to 150 days after last dose. Phase 2 (NEJM 2025, PMID: 40549887): 592 participants across obesity and obesity+T2D cohorts over 52 weeks with up to 21.6% weight loss. Phase 3 MARITIME-1 (~3,500 patients, 72 weeks) and MARITIME-2 (~999 patients, obesity+T2D) started March 2025. MARITIME-CV, MARITIME-HF, OSA, and CKD programs also planned.

Animal / Preclinical

Strong. Preclinical data in DIO mice and cynomolgus monkeys confirmed GIPR antagonism + GLP-1R agonism mechanism, weight reduction, and improved metabolic parameters (Véniant et al., Nat Metab 2024).

Mechanistic Rationale

Strong but paradoxical. Both GIPR antagonism (MariTide) and GIPR agonism (tirzepatide) produce weight loss — both are clinically validated despite opposite receptor directions. Characterization studies of GIPR variants (Kizilkaya et al., Nat Metab 2024, PMID: 38871982) support the antagonism approach, while tirzepatide's success validates agonism. The antibody-peptide conjugate format is well-established in biologics but novel in obesity.

Forms & Administration

MariTide is administered as a once-monthly (Q4W) or once-every-8-weeks (Q8W) subcutaneous injection. Phase 2 tested doses from 140 mg to 420 mg with dose escalation schemes. Currently only available through clinical trials.

Use Cases & Evidence Levels

Once-monthly dosing (vs weekly for other incretins)

Moderate70%

Weight loss rivaling tirzepatide with less frequent dosing

Moderate70%

Novel GIPR antagonism hypothesis (opposite of tirzepatide)

Moderate70%

Prolonged post-treatment effect (weight maintained up to 150 days after last dose in Phase 1)

Preliminary30%

Type 2 diabetes control (HbA1c -1.2 to -1.6 in Phase 2)

Moderate70%

Safety Profile

Safety Information

Common Side Effects

Nausea (most common, predominantly after first dose)VomitingConstipationMostly mild, transientDose escalation significantly reduced GI AEs

Cautions

• Not FDA-approved — investigational drug in Phase 3
• 11% discontinuation due to AEs in dose-escalation arms
• GI side effects may be harder to manage given monthly dosing (cannot quickly adjust dose)
• Long half-life (~21 days) means drug persists weeks after discontinuation

What We Don't Know

Published Research

8 studies

Obesity pharmacotherapy reimagined: The era of multi-receptor agonists and next-generation metabolic modulators.

ReviewPMID: 41948476

A metabolic comparison of GIPR agonism versus GIPR antagonism in male mice.

PreclinicalPMID: 41287212

Novel GLP-1-based Medications for Type 2 Diabetes and Obesity.

ReviewPMID: 41054801

Once-Monthly Maridebart Cafraglutide for the Treatment of Obesity — A Phase 2 Trial.

Phase 2, 592 participants, 52 weeks — up to 16.2% weight loss (treatment-policy), ~21.6% (efficacy estimand)

Randomized Controlled TrialPMID: 40549887

The Premise of the Paradox: Examining the Evidence That Motivated GIPR Agonist and Antagonist Drug Development Programs.

ReviewPMID: 40507574

Characterization of genetic variants of GIPR reveals a contribution of β-arrestin to metabolic phenotypes.

PreclinicalPMID: 38871982

A GIPR antagonist conjugated to GLP-1 analogues promotes weight loss with improved metabolic parameters in preclinical and phase 1 settings.

Preclinical/Phase 1PMID: 38316982

Beyond the pancreas: contrasting cardiometabolic actions of GIP and GLP1.

ReviewPMID: 36509857

Related Peptides

Tirzepatide

StrongBeginner

A dual GIP/GLP-1 receptor agonist FDA-approved for diabetes and weight management, producing the largest weight loss seen in clinical trials.

Semaglutide

StrongBeginner

A GLP-1 receptor agonist FDA-approved for type 2 diabetes and chronic weight management, one of the most widely prescribed peptide drugs.

Retatrutide

Emerging

An investigational triple agonist (GIP/GLP-1/glucagon) from Eli Lilly. Not FDA-approved. Phase III TRIUMPH-4 results showed 23.7% weight loss — the most of any obesity drug in development.

Mazdutide

Moderate

The world's first approved dual GLP-1/glucagon receptor agonist, developed by Innovent Biologics (China). Approved in China for obesity and type 2 diabetes. Phase 3 trials showed up to 20.1% weight loss.

Brenipatide

Limited

A once-monthly dual GIP/GLP-1 receptor agonist from Eli Lilly, in Phase 3 trials for alcohol use disorder and bipolar disorder, with additional studies in obesity, asthma, and smoking cessation.

CT-388

Moderate

Roche/Genentech's next-generation dual GLP-1/GIP receptor agonist. Phase 2 showed 22.5% placebo-adjusted weight loss at 48 weeks — competitive with retatrutide. Phase 3 ENITH program starts Q1 2026.

Quick Facts

Class: Antibody-Peptide Conjugate
Evidence: Moderate
Safety: Limited Data
Updated: Apr 2026
Citations: 8PubMed

Also known as

Maridebart CafraglutideAMG 133

Evidence Score

Overall Confidence60%

Clinical Trials

View Clinical Trials

Links to ClinicalTrials.gov for reference. Listing does not imply endorsement.