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Retatrutide vs MariTide: A Weekly Triple Agonist Against a Monthly GIP Antagonist

Retatrutide and MariTide (maridebart cafraglutide, AMG 133) arrive at large weight reductions by opposite routes. Retatrutide is a weekly peptide that activates the GIP, GLP-1 and glucagon receptors; MariTide is a monthly peptide–antibody conjugate that activates GLP-1 and blocks GIP . In separate Phase 2 trials retatrutide reached 24.2% at 48 weeks and MariTide up to about 20% at 52 weeks. Neither is approved, no head-to-head results exist, and New-U does not sell MariTide.

No head-to-head results exist. The two Phase 2 trials differ in size, dose design and analysis method; both figures are best-arm results. Cross-trial percentages are indicative only. Research context; nothing here is medical or dosing guidance. Regulatory and trial status is as of September 2026.

At a glance

Retatrutide MariTide Receptor profile GIP + GLP-1 + glucagon agonist GLP-1 agonist + GIP antagonist Format Lipidated peptide (39 amino acids) Peptide–antibody conjugate Developer Eli Lilly (LY3437943) Amgen (AMG 133) Half-life ~6 days ~21 days Cadence Once-weekly (trials) ~Once-monthly Phase 2, obesity without diabetes 24.2% at 48 wk (12 mg arm) Up to ~20% at 52 wk Status Phase 3 (TRIUMPH); no approval Phase 3 (MARITIME); no approval Research access GLP1-RC-RT (retatrutide reference) Not sold: proprietary conjugate

The GIP question

Tirzepatide and retatrutide activate the GIP receptor. MariTide blocks it while still activating GLP-1. Both designs were associated with large mean weight reductions in trials, which is the field’s open puzzle. The leading hypotheses are that chronic GIP agonism ends up desensitising the receptor, so agonist and antagonist converge on a similar downstream state, and that central and peripheral GIP signalling pull in different directions. The answer has not been settled, and no study has yet isolated the contribution of the GIP arm in either design.

Retatrutide adds a third arm (glucagon) to the agonist route. MariTide takes the opposite position on GIP and adds nothing on glucagon. The two molecules therefore test different hypotheses about the same class, and only trials designed to compare them could say which is right.

Weekly peptide vs monthly conjugate

Most obesity drugs are peptides. MariTide is a monoclonal-antibody scaffold with GLP-1 analogue peptides chemically attached. Antibodies circulate for weeks, so the conjugate’s half-life is roughly 21 days as reported by Amgen — about three times that of semaglutide (~7 days) and more than three times retatrutide’s ~6 days — which is what makes once-monthly dosing plausible.

MariTide is a proprietary Amgen antibody conjugate; there is no licensed source for it outside Amgen’s clinical programme.

What the trials showed

Retatrutide (Phase 2, NEJM 2023, n=338): 17.1% (4 mg), 22.8% (8 mg) and 24.2% (12 mg) mean weight reduction at 48 weeks against 2.1% on placebo, with no plateau. Phase 3 TRIUMPH-1 has reported 28.3% at 80 weeks (12 mg, sponsor topline).

MariTide (Phase 2, NEJM 2025): up to about 20% mean weight reduction at 52 weeks on the efficacy estimand in people with obesity but not diabetes (placebo about 2.6%), and up to about 17% in people with type 2 diabetes (placebo 1.4%). The weight curve had not flattened at 52 weeks.

These are the closest-timed pair of results for the two compounds — both Phase 2, both about a year, both in obesity without diabetes — and they are still different trials with different dose designs. MariTide’s Phase 3 programme, MARITIME, runs 72-week studies; retatrutide’s TRIUMPH programme is further along on reported toplines.

Research access

MariTide is a proprietary Amgen antibody conjugate and New-U does not sell it. Treat any “buy MariTide” listing with caution: there is no licensed MariTide product for a supplier to sell. The MariTide research guide has the full listing red-flag checklist.

Research takeaway

Retatrutide activates GIP, GLP-1 and glucagon weekly; MariTide activates GLP-1 and blocks GIP about monthly.

Both showed roughly 20% or more at about one year in separate Phase 2 trials. The figures are not a ranking.

The GIP agonist-versus-antagonist puzzle is unresolved.

Neither is approved, and MariTide is not sold.

Primary sources

New England Journal of Medicine — Triple–Hormone-Receptor Agonist Retatrutide for Obesity (Jastreboff et al., 2023)

Eli Lilly — TRIUMPH-1 topline results

New England Journal of Medicine — Once-Monthly Maridebart Cafraglutide for the Treatment of Obesity — A Phase 2 Trial

Amgen — Phase 2 results presented at the ADA 85th Scientific Sessions

Retatrutide as a research reference (GLP1-RC-RT)

New-U catalogues laboratory research material under GLP1-RC-RT (retatrutide reference). MariTide is a proprietary Amgen conjugate and is not sold. The trial results above describe the sponsors’ investigational products, not this material. Published Certificates of Analysis are available for the batches listed in the COA library. Research use only – all claims made on this site are for testing and research use only.

Frequently asked questions

Is MariTide better than retatrutide?

No trial has compared them. Separate Phase 2 trials reported up to about 20% for MariTide at 52 weeks and 24.2% for retatrutide at 48 weeks, but the designs differ. Neither is approved. Research context only.

What dosing interval has each been studied at?

MariTide is a peptide–antibody conjugate with a half-life near 21 days (as reported by Amgen), studied at roughly monthly intervals. Retatrutide has a half-life near 6 days and was studied at weekly intervals.

Why does MariTide block GIP when retatrutide activates it?

It is an open research question. Proposed explanations include GIP-receptor desensitisation under chronic agonism and differing central and peripheral GIP signalling; both designs were associated with weight loss in trials.

Is MariTide approved?

As of September 2026, no. The sources reviewed report no marketing authorisation, and MariTide is in the Phase 3 MARITIME programme.

Can MariTide be bought as a research compound?

No. It is a proprietary Amgen antibody conjugate and New-U does not sell it.

External links are provided for research reference only; New-U is not affiliated with the cited organisations. All figures are published trial results shown for research context, not dosing guidance. New-U Research Compounds supplies research compounds strictly for laboratory research use only — not for human consumption .

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Buy Retatrutide from New-U Research Compounds

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Research peptides at >99% HPLC-verified purity, third-party tested by Janoshik Analytical & Freedom Diagnostics, with Certificates of Analysis published per released batch. Supplied strictly for laboratory research use.

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