Maridebart cafraglutide — known in development as MariTide, formerly AMG 133 — is not a conventional incretin peptide. It is an antibody–peptide conjugate: an anti-GIPR antibody backbone with two GLP-1 receptor agonist peptides attached. The design produces an unusual pharmacology. Where tirzepatide activates the GIP receptor, MariTide blocks it (GIPR antagonism) while activating GLP-1 — a combination Amgen has argued reflects human-genetics evidence rather than the agonist-first consensus.
Why the format matters
Conjugating peptide agonists to an antibody extends the circulating half-life to roughly three weeks, which supports once-monthly dosing and, in principle, less frequent administration. That is a departure from the weekly injection schedule of the licensed GLP-1 and dual agonists. The peptide payload provides the receptor activity; the antibody scaffold provides the pharmacokinetics.
What the trial record shows
A Phase 2 trial of once-monthly maridebart cafraglutide in adults with obesity, with or without type 2 diabetes, was published in the New England Journal of Medicine in 2025 (Jastreboff et al.; PMID 40549887). It reported substantial weight reduction with monthly dosing and no observed plateau at 52 weeks. The Phase 3 MARITIME programme is now running across chronic weight management, type 2 diabetes, cardiovascular outcomes, heart failure and obstructive sleep apnoea; the MARITIME-OSA-1 and MARITIME-OSA-2 studies are enrolling adults with moderate-to-severe obstructive sleep apnoea and a BMI of 27 or above. No Phase 3 efficacy readout has been published.
Regulatory position in the UK
Maridebart cafraglutide is investigational and has no marketing authorisation anywhere, including the UK. It is not available on prescription, and because it is an antibody–peptide conjugate it cannot be reproduced by conventional peptide synthesis or compounding — any product sold as 'MariTide' or 'AMG 133' is not the clinical molecule. It is discussed here as a research compound, for research use only. Under the Medicines Act 1968 and the Human Medicines Regulations 2012, unlicensed supply for human use is an offence.
Evidence grade
Preclinical and Phase 2 human data; no Phase 3 efficacy data and no long-term safety data. On the published record the evidence is Limited. At this stage the mechanism is the more interesting story than the evidence.
This article is AI-researched and editorially reviewed. It is provided for research and educational purposes only and is not medical advice. Research peptides are not licensed for human consumption in the UK.