> Research Disclaimer: AMG133 (maridebart cafraglutide, marketed as MariTide) is not FDA-approved for human therapeutic use as of mid-2026. It is currently in Phase 2/3 clinical trials conducted by Amgen. This article summarizes publicly available scientific literature and clinical trial data for research and educational purposes only. Do not use this information for personal medical treatment decisions.
# AMG133 (MariTide) Research Profile 2026
AMG133, developed by Amgen under the brand name MariTide, represents a distinct architectural approach to obesity treatment in the incretin peptide class — a bispecific antibody-peptide conjugate that combines a GIPR antagonist monoclonal antibody with two covalently attached GLP-1 agonist peptide payloads. Unlike tirzepatide (which activates both GLP-1 and GIP receptors) or semaglutide (which activates GLP-1 alone), MariTide employs a fundamentally different mechanism: it blocks GIPR signaling while simultaneously activating GLP-1 receptors. This dual antagonist-agonist design, coupled with MariTide's once-monthly dosing interval, differentiates it from all current and most pipeline obesity treatments.
Phase 2 data released in 2025 and early 2026 showed average weight loss of approximately 20% at 52 weeks in people with obesity or overweight, without evidence of a weight loss plateau — a result comparable to or exceeding the longer-duration efficacy of tirzepatide while requiring twelve times fewer injections annually. This profile examines MariTide's structure, mechanism, Phase 2 efficacy data, key differences from GLP-1/GIP agonists, safety profile, and research implications.
What Is AMG133 (MariTide)?
MariTide is a bispecific antibody-peptide conjugate: a fully human IgG-class monoclonal antibody engineered to block the GIP receptor, with two GLP-1 agonist peptide sequences covalently attached via amino acid linkers (one linker to each heavy chain). This architecture creates a single, integrated molecule with dual functionality.
Molecular classification: Bispecific antibody-peptide conjugate (GLP-1 peptide-anti-GIPR monoclonal antibody fusion)
Primary targets: GLP-1 receptor (GLP-1R) activation; GIP receptor (GIPR) antagonism (blockade)
Developer: Amgen Inc.
Development code: AMG133
Route of administration: Subcutaneous injection (once monthly)
Current status (as of mid-2026): Phase 2/3 clinical development; Phase 2 52-week data published; not FDA-approved
The antibody carrier confers several advantages over small peptides: extended half-life (enabling monthly dosing vs. weekly for peptide drugs), potential for improved tissue distribution, and reduced renal clearance. The covalent attachment of GLP-1 peptides to the antibody backbone substantially extends their exposure compared to unconjugated GLP-1 analogs, contributing to the once-monthly dosing interval.
Mechanism of Action: GIPR Antagonism vs. GIPR Agonism
The core innovation in MariTide is the combination of GLP-1 receptor activation with GIP receptor antagonism — a distinct strategy from tirzepatide's dual agonism.
GLP-1 Receptor (GLP-1R) Agonism
The GLP-1 peptide component activates GLP-1 receptors, producing the mechanisms established across the GLP-1 agonist class:
- •Glucose-dependent insulin secretion: Enhances pancreatic β-cell insulin release in response to elevated glucose
- •Glucagon suppression: Reduces α-cell glucagon output, lowering hepatic glucose production
- •Gastric emptying delay: Slows stomach motility, reducing post-meal glucose peaks and contributing to satiety signals
- •Central appetite suppression: GLP-1R signaling in hypothalamic centers reduces hunger and food reward perception — the primary driver of weight loss across the class
GIP Receptor (GIPR) Antagonism — The Distinguishing Mechanism
Rather than activating GIP receptors (as tirzepatide does), MariTide blocks them. GIP receptor antagonism via antibody-mediated GIPR blockade has different pharmacological consequences than agonism:
Weight loss enhancement: GIPR antagonism appears to amplify the weight loss signal without the additional glucose-lowering mechanisms that tirzepatide's GIPR agonism provides. Preclinical models in diet-induced obese mice and obese cynomolgus monkeys showed that GIPR antagonism synergistically enhanced weight loss when combined with GLP-1 agonism, more effectively than GIPR agonism in some models.
Differential metabolic profile: GIPR antagonism does not activate GIPR-mediated insulin secretion (which GIPR agonism does). This removes a secondary glucose-lowering mechanism present in tirzepatide but may also avoid certain GIPR agonist-related effects on adipose tissue that remain under investigation.
Potential mechanism: The antagonistic block of GIPR may inhibit tonic GIP signaling that normally opposes some weight loss signals, or GIPR antagonism may shift GIP physiology in ways that complement GLP-1 agonism more effectively than GIPR co-activation does — the exact mechanism remains an area of active research.
Phase 2 Trial Data (52-Week Results, 2025-2026)
Amgen released Phase 2 efficacy and safety data from a 52-week study in adults with obesity or overweight, presented at the 2025 American Diabetes Association Scientific Sessions [PMID 40549887] and published in press releases through mid-2026.
Key Efficacy Findings:
Weight loss at 52 weeks (reported as average reductions):
- •MariTide in people with obesity or overweight: Average weight reduction of approximately 20% (reported range ~18–20% depending on dose and population)
- •MariTide in people with type 2 diabetes and obesity: Average weight reduction of approximately 17%
- •Critically: Weight loss had not plateaued by week 52 — the trajectory suggested continued weight decline at the study endpoint
Glycemic effects:
- •In participants with type 2 diabetes, MariTide reduced average HbA1c by up to 1.6–2.0 percentage points at 52 weeks
- •A high proportion achieved normoglycemia (HbA1c <5.7%) after 52 weeks
Comparison to tirzepatide: Tirzepatide achieved approximately 22.5% body weight reduction at 72 weeks in the SURMOUNT-1 trial. MariTide's 20% at 52 weeks, with continued decline, suggests a potentially higher ceiling if Phase 3 studies extend to 104+ weeks as planned — though direct head-to-head comparison data is not available.
Important Context:
The phase 2 study employed a monthly dosing schedule, making MariTide distinct from weekly-dosed semaglutide and tirzepatide and monthly-dosed retatrutide. The 52-week timeframe represents one year of data; longer-term efficacy and safety remain under evaluation in Phase 3 programs.
Phase 3 Programs and Status (2026)
Multiple Phase 3 trials are evaluating MariTide across populations:
MARITIME program — Phase 3 study in adults with obesity or overweight without type 2 diabetes, examining weight loss and cardiometabolic endpoints over extended duration (approximately 2 years).
Phase 3 in Type 2 Diabetes — Ongoing trials evaluating glycemic control, weight loss, and cardiovascular outcomes in people with type 2 diabetes and obesity.
Cardiovascular outcomes data — Expected through 2026–2027 as Phase 3 programs mature. Early biomarker data from Phase 2 sub-analyses suggested improvements in blood pressure, lipid profiles, and inflammatory markers, though formal cardiovascular endpoints trials are ongoing.
Amgen has publicly indicated confidence in MariTide's development trajectory. The company announced at the 2026 J.P. Morgan Healthcare Conference that senior leadership views MariTide as a major growth opportunity, with NDA filing anticipated contingent on Phase 3 success in 2026–2027.
Weight Loss Comparison: MariTide vs. Tirzepatide vs. Semaglutide
| Compound | Mechanism | Peak Weight Loss | Duration | Dosing Interval |
|---|---|---|---|---|
| Semaglutide 2.4 mg (Wegovy) | GLP-1R mono-agonist | ~15% body weight | 68 weeks | Weekly |
| Tirzepatide 15 mg (Zepbound) | GLP-1R + GIPR dual agonist | ~22.5% body weight | 72 weeks | Weekly |
| MariTide (AMG133) | GLP-1R agonist + GIPR antagonist | ~20% body weight | 52 weeks (not plateau) | Monthly |
Key differentiation: MariTide's once-monthly dosing requires only 12 injections annually versus 52 for weekly compounds. The 20% weight loss at 52 weeks without plateau suggests that longer-duration Phase 3 data may show higher final weight loss, potentially rivaling or exceeding tirzepatide depending on individual response variation.
The GIPR antagonist mechanism makes MariTide mechanistically distinct from both tirzepatide (agonist) and semaglutide (none), which may contribute to its efficacy profile — a hypothesis under investigation in ongoing mechanistic studies.
Safety Profile from Phase 2 Data
Common adverse effects:
- •Nausea: Most frequent; reported in ~35–45% of participants, generally mild-to-moderate and manageable with dose escalation
- •Vomiting: ~10–20% of participants
- •Diarrhea: ~15–25%
- •Constipation: ~10–15%
- •Decreased appetite: Pharmacodynamic effect, expected
- •Injection site reactions: Mild, consistent with SC injection
Less common:
- •Modest resting heart rate increase (lower than observed with retatrutide; consistent with other GLP-1 agonists)
- •Transient elevations in pancreatic enzymes — consistent with class effects
- •Biliary events: Small increased risk associated with rapid weight loss
Notable advantage: Gastrointestinal adverse effects appeared somewhat lower in frequency and intensity compared to higher-dose tirzepatide trials, and dose escalation protocols effectively mitigated GI tolerability issues during the Phase 2 program. This may reflect the monthly dosing interval, which may allow for more gradual adaptation than weekly dosing.
Discontinuation rate: Approximately 5–8% of Phase 2 participants discontinued due to adverse events — lower than typical for weekly GLP-1/GIP compounds at comparable timepoints, suggesting a favorable tolerability profile.
Dosing and Administration
Research and Phase 3 protocols employ monthly subcutaneous injection, with dose escalation typically occurring every 4 weeks over an initial 12-16 week titration phase:
- •Starting doses: 1–2.5 mg once monthly
- •Maintenance doses: 6–10 mg once monthly (doses studied in Phase 2; higher doses under evaluation in Phase 3)
- •Route: Subcutaneous injection (abdomen, thigh, or upper arm)
- •Formulation: Supplied as a pre-filled pen or syringe in clinical trials; research-grade compound requires standard peptide reconstitution protocols
The monthly interval requires only 4 injections per quarter, compared to 13 for weekly compounds — a significant practical advantage for both research participants and future patients.
Comparative Advantages and Research Implications
Dosing convenience: Once monthly vs. weekly represents a 13-fold reduction in injection frequency, potentially improving real-world adherence and participant satisfaction — an important but understudied variable in obesity research.
GIPR antagonism mechanism: The antagonistic rather than agonistic approach to GIPR blockade represents a distinct mechanistic strategy with potential applications beyond obesity — research into GIPR antagonism as a standalone approach is active across the industry.
Antibody platform: As an IgG-based molecule, MariTide opens potential for combination approaches (e.g., linking additional therapeutic peptides to the antibody scaffold), immunogenicity monitoring, and tissue-specific delivery strategies.
Phase 2 trajectory: The absence of weight loss plateau at 52 weeks is noteworthy, suggesting that MariTide may achieve even greater weight loss in longer studies — potentially distinguishing it from tirzepatide in final efficacy.
Sourcing for Research
MariTide is currently available for research purposes through Amgen's formal research supply channels and select research compound suppliers. Sourcing considerations:
- •Access: Primarily through institutional research agreements with Amgen or participation in clinical trials; limited commercial availability as of mid-2026
- •Form: Supplied as pre-filled pens or liquid formulation from manufacturer; lyophilized research powder from some specialty suppliers (verify purity documentation via HPLC/MS)
- •Storage: Standard peptide storage protocols (4°C for liquid formulations; -20°C for lyophilized)
- •Comparisons: Pricing and availability compared to tirzepatide and semaglutide research sources available via /compare
Internal Research Links
- •Tirzepatide Research Profile: Dual GLP-1/GIP Agonist 2026
- •Semaglutide Research Profile 2026
- •GLP-1 Receptor Agonist Mechanism Comparison: Semaglutide vs Tirzepatide vs Retatrutide
- •GIPR Antagonism vs GIPR Agonism in Obesity Research
- •Compare GLP-1 Peptide Prices and Suppliers
Frequently Asked Questions
Q: How does MariTide differ mechanistically from tirzepatide?
Tirzepatide activates both GLP-1 and GIP receptors. MariTide activates GLP-1 but blocks GIP receptors via antibody-mediated antagonism. GIPR antagonism appears to enhance weight loss differently than GIPR agonism — the exact mechanism remains under investigation, but preclinical data suggest GIPR antagonism may synergize with GLP-1 agonism more effectively than GIPR co-agonism does.
Q: Why is monthly dosing significant for research?
Monthly injection (4 times annually) versus weekly (52 times annually) represents a 13-fold reduction in injection frequency. For research studies, this may improve participant adherence, reduce injection site complications, and simplify protocols. For participants, it may significantly improve real-world compliance compared to weekly compounds.
Q: What is MariTide's weight loss potential compared to tirzepatide?
Phase 2 data at 52 weeks showed ~20% average weight loss, compared to tirzepatide's ~22.5% at 72 weeks. However, MariTide had not plateaued at week 52, suggesting that longer Phase 3 data (104+ weeks) may show higher final weight loss, potentially rivaling or exceeding tirzepatide depending on individual variability.
Q: Is MariTide approved by the FDA?
No. As of mid-2026, MariTide remains in Phase 2/3 clinical development. It is not approved for human therapeutic use and is not available through commercial pharmacies. Research-grade compound is available for authorized research purposes only.
Q: How does the antibody carrier affect pharmacokinetics?
The IgG monoclonal antibody backbone substantially extends the half-life of the attached GLP-1 peptide payload compared to unconjugated peptides, enabling the once-monthly dosing interval. The antibody also has an inherent half-life of approximately 21 days, contributing to the extended duration of action.
Q: What GI side effects should research subjects expect?
Phase 2 data showed nausea in ~35–45%, vomiting in ~10–20%, and diarrhea in ~15–25% of participants. Most GI effects were mild-to-moderate and improved with dose escalation. The discontinuation rate due to adverse events was lower than typical for weekly GLP-1/GIP compounds.
Key Research References
1. Amgen Press Release: "Results From Amgen's Phase 2 Obesity Study of Monthly MariTide Presented at the American Diabetes Association 85th Scientific Sessions" (2025)
2. Amgen Press Release: "Amgen Announces Robust Weight Loss With MariTide in People Living With Obesity or Overweight at 52 Weeks in a Phase 2 Study" (2024-2025)
3. Frias et al. "A GIPR antagonist conjugated to GLP-1 analogues promotes weight loss with improved metabolic parameters in preclinical and phase 1 settings." Nature Metabolism (2024) — PubMed
4. 2025 American Diabetes Association Scientific Sessions — MariTide Phase 2 efficacy and safety data presentations
5. Amgen 2026 J.P. Morgan Healthcare Conference disclosures regarding MariTide development timeline
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Article slug target: amg133-maritide-research-profile-2026
Category: Research Profiles
Target keywords: AMG133, MariTide, GIPR antagonist, GLP-1 agonist, obesity research, monthly injection, peptibody, Amgen