Investigational — not available anywhere
This compound is not approved for any use and is not currently sold by any vendor, including research-chemical and RUO (“research use only”) sellers. Evidence for MariTide comes from Amgen’s own published and presented clinical trial data, not from independent human trials or vendor sources. Because MariTide is a large antibody-peptide conjugate manufactured under Amgen’s own biologics process, it is very unlikely to appear from grey-market peptide vendors the way small synthetic peptides sometimes do.
MariTide (maridebart cafraglutide, development code AMG 133) is a once-monthly, self-injected antibody-peptide conjugate being developed by Amgen for weight management, with and without type 2 diabetes. It combines a monoclonal antibody that blocks the GIP receptor with two GLP-1 receptor agonist peptides attached to that antibody, giving it a long enough half-life (about three weeks) to support once-a-month or less-frequent dosing. In a 52-week Phase 2 trial, participants with obesity but no diabetes lost 12.3% to 16.2% of their body weight on average depending on dose, against 2.5% on placebo; Amgen has since moved MariTide into the large Phase 3 MARITIME program.
Research snapshot
| Peptide category | Antibody-peptide conjugate (bispecific: GIP receptor antagonist antibody + GLP-1 receptor agonist peptides) |
| Primary research interest | Obesity and weight management, with and without type 2 diabetes |
| Highest available evidence | Published/presented human Phase 2 clinical trial data |
| Human research available | Yes — completed Phase 1 and Phase 2 trials; Phase 3 MARITIME program ongoing |
| Development status | Phase 3 (MARITIME-1 and MARITIME-2, plus additional cardiovascular, heart failure, kidney disease, and sleep apnea studies) |
| Regulatory status | Not approved anywhere; investigational only |
| Last reviewed | 2026-09-27 |
Technical identity
| Primary name | Maridebart cafraglutide |
| Alternative names | MariTide, AMG 133 |
| Peptide sequence | Not applicable in the usual sense — MariTide is not a single peptide chain. It is a monoclonal antibody scaffold with two GLP-1 receptor agonist peptide arms attached; the peptide arm and antibody sequences have not been published. |
| Molecular formula | Not publicly disclosed. As an antibody-peptide conjugate (a large biologic, not a small synthetic peptide), it would not be expected to have a simple molecular formula the way a short peptide does. |
| Molecular weight | Not publicly disclosed |
| CAS Registry Number | Not reliably established |
| PubChem CID | Not reliably established |
| UNII | Not available |
| DrugBank ID | Not available |
| Chemical modifications | Two GLP-1 analogue agonist peptides conjugated to a fully human anti-GIP receptor monoclonal antibody via amino-acid linkers, extending half-life to roughly 21 days |
| Peptide class | Antibody-peptide conjugate; bispecific GIP receptor antagonist / GLP-1 receptor agonist |
| Primary biological target | GIP receptor (antagonized) and GLP-1 receptor (agonized) |
| Developer or originator | Amgen |
| Development status | Phase 3 (MARITIME program) |
What is MariTide?
MariTide is Amgen’s investigational medicine for obesity and weight management, known chemically as maridebart cafraglutide and carried through early development under the code AMG 133. It does not work the way most GLP-1 drugs on the market do. Instead of being a single peptide that activates one receptor, MariTide is an antibody-peptide conjugate: a fully human monoclonal antibody that blocks (antagonizes) the GIP receptor, with two GLP-1 receptor agonist peptides chemically attached to that antibody using amino-acid linkers.
That antibody backbone is what makes MariTide unusual among obesity drugs in development. Antibodies naturally stay in the bloodstream far longer than small peptides do, and Amgen has reported a half-life of roughly 21 days for MariTide — about three times longer than currently approved weekly GLP-1 medications like semaglutide or tirzepatide. That is the basis for Amgen’s stated goal of once-monthly, or even less frequent, dosing.
Amgen first described AMG 133 publicly in 2023, and the compound completed Phase 1 and a 592-participant Phase 2 dose-ranging trial before advancing into Phase 3. The Phase 3 MARITIME program, which Amgen has called one of the largest clinical trial programs in its 45-year history, now spans weight management with and without type 2 diabetes, plus additional studies in cardiovascular disease, heart failure, chronic kidney disease, and obstructive sleep apnea. Amgen has publicly discussed a possible 2027–2028 regulatory filing and launch window, though that has not been confirmed by any regulatory body.
How does it work?
Plain-English explanation
Think of MariTide as two different weight-loss signals riding on one long-lasting delivery vehicle. The antibody part sticks around in the blood for weeks and does the job of blocking a hormone receptor (GIP) that, in this antagonist role, appears to help the body respond better to the second signal. The two peptide arms attached to that antibody activate GLP-1 receptors, the same receptors that drugs like Ozempic and Wegovy activate, which slow stomach emptying, reduce appetite, and help regulate blood sugar. Because the whole package is built on an antibody rather than a short peptide, it clears the body much more slowly, so one injection can keep working for weeks instead of days.
Technical explanation
MariTide pairs a fully human anti-GIPR monoclonal antibody, acting as a GIP receptor antagonist, with two GLP-1 analogue agonist peptides conjugated to the antibody via amino-acid linkers. This differs mechanistically from tirzepatide, which is a single small molecule that agonizes both the GIP and GLP-1 receptors; MariTide instead blocks GIP signaling while agonizing GLP-1 signaling, an approach based on preclinical and genetic evidence suggesting GIP receptor antagonism can be additive with GLP-1 agonism for weight loss. The antibody scaffold gives MariTide an approximate 21-day half-life, roughly three times that of once-weekly GLP-1 therapies, which Amgen has cited as the pharmacological basis for exploring monthly or less-frequent subcutaneous dosing in the Phase 3 program.
Potential benefits and research applications
Weight loss in obesity, without diabetes
In Amgen’s 52-week Phase 2 trial, 465 participants with obesity but no type 2 diabetes were randomized to placebo or one of several MariTide dose regimens (140 mg, 280 mg, or 420 mg subcutaneously every four weeks, with or without a dose-escalation lead-in, plus a 420 mg every-eight-weeks arm). Average weight loss across the active dose arms ranged from 12.3% to 16.2% at week 52, compared with 2.5% for placebo, and some individual participants lost close to 20%. Weight loss had not clearly plateaued by week 52 in the higher-dose groups, which is part of why Amgen moved forward into Phase 3 rather than settling on a single dose at this stage. This is human, randomized, placebo-controlled Phase 2 evidence — the strongest tier available for MariTide so far, but still short of an approved, published Phase 3 result.
Weight loss and glycemic control with type 2 diabetes
A second Phase 2 cohort of 127 participants with obesity and type 2 diabetes was studied on the same dosing schedule. Average weight loss in this cohort ranged from 8.4% to 12.3% (versus 1.7% on placebo), with maximum individual losses around 17%, and HbA1c fell by 1.2 to 1.6 percentage points on active treatment. This is again human Phase 2 evidence, and it is the basis for the separate MARITIME-2 Phase 3 trial in this population.
Cardiovascular, kidney, and other outcomes
Amgen has stated the MARITIME Phase 3 program includes additional trials investigating MariTide in cardiovascular disease, heart failure, chronic kidney disease, and obstructive sleep apnea, extending the obesity-adjacent outcomes work already established for other GLP-1 therapies to MariTide specifically. As of this review, these studies are registered and underway; no results have been published, so this is registered-but-unpublished human trial evidence, not yet a demonstrated benefit.
What dosage information circulates?
Figures in this section summarize amounts and schedules reported in Amgen’s published and presented clinical trial data. Their inclusion documents what is reported and does not establish that any particular dose is the one that will eventually be approved. MariTide is not sold anywhere, so there is no community-reported or vendor-reported dosing to include here — every figure below traces back to Amgen’s own trials.
The clearest pattern from Phase 2: three monthly dose levels (140 mg, 280 mg, and 420 mg) were tested, each with and without a dose-escalation lead-in period, plus a lower-frequency 420 mg every-eight-weeks arm. Amgen has said gastrointestinal side effects were less frequent with dose escalation and a lower starting dose, which is likely why escalation is being carried into Phase 3. Amgen has not yet disclosed which dose or doses were selected for the Phase 3 MARITIME-1 and MARITIME-2 trials, or the specific per-arm milligram doses being used in those studies.
| Reported use or research objective | Route reported | Amount reported | Frequency reported | Reported duration | Evidence or source category |
|---|---|---|---|---|---|
| Phase 2, obesity without type 2 diabetes | Subcutaneous | 140 mg, 280 mg, or 420 mg, with or without a dose-escalation lead-in | Every 4 weeks (one arm: 420 mg every 8 weeks) | 52 weeks | Company-reported, congress-presented human clinical trial |
| Phase 2, obesity with type 2 diabetes | Subcutaneous | Same dose arms as the non-diabetes cohort | Every 4 weeks (one arm: 420 mg every 8 weeks) | 52 weeks | Company-reported, congress-presented human clinical trial |
| Phase 3 MARITIME-1, overweight or obesity | Subcutaneous | Not yet disclosed | Monthly or less frequent (stated program goal) | Ongoing | Registered, unpublished human trial |
| Phase 3 MARITIME-2, overweight or obesity with type 2 diabetes | Subcutaneous | Not yet disclosed | Monthly or less frequent (stated program goal) | Ongoing | Registered, unpublished human trial |
Side effects, risks, and limitations
In the Phase 2 trial, gastrointestinal adverse events (nausea, vomiting, diarrhea, constipation) were the most commonly reported side effects, consistent with other GLP-1 receptor agonists. Amgen has reported that these events occurred less frequently when doses were escalated gradually and when treatment started at a lower dose, and that no new safety signals emerged through 52 weeks. As an antibody-based biologic rather than a small peptide, MariTide also carries a theoretical risk of anti-drug antibody formation over time, which has not been fully characterized in public disclosures. Long-term safety beyond 52 weeks, and safety in the cardiovascular, kidney, and sleep apnea populations now being studied, is not yet established. No independent, non-Amgen safety data exists, and no real-world or post-market safety data exists since the drug is not approved anywhere.
Regulatory and developmental status
MariTide is not approved for any use in any country. It is in Phase 3 development, with the MARITIME-1 trial studying adults with overweight or obesity and MARITIME-2 studying adults with overweight or obesity and type 2 diabetes, alongside additional Phase 3 studies in cardiovascular disease, heart failure, chronic kidney disease, and obstructive sleep apnea. Amgen has publicly referenced a possible 2027–2028 filing and launch window based on the pace of the Phase 3 program, but no regulatory submission has been made or confirmed as of this review, and timelines for large multi-study programs like this commonly shift.
Frequently asked questions
What is MariTide?
MariTide (maridebart cafraglutide, AMG 133) is an investigational antibody-peptide conjugate from Amgen being studied for weight management, combining a GIP receptor-blocking antibody with two attached GLP-1 receptor agonist peptides.
How does MariTide work?
It blocks the GIP receptor while activating the GLP-1 receptor, using an antibody backbone that keeps it active in the body for weeks rather than days, supporting monthly or less-frequent dosing.
What dosage has been studied?
Phase 2 tested 140 mg, 280 mg, and 420 mg subcutaneously every four weeks (with and without dose escalation), plus a 420 mg every-eight-weeks arm. Amgen has not disclosed the specific doses used in the ongoing Phase 3 MARITIME trials.
How much weight loss has MariTide produced in trials?
In the 52-week Phase 2 trial, participants with obesity but no diabetes lost an average of 12.3% to 16.2% of body weight depending on dose, versus 2.5% on placebo. Participants with obesity and type 2 diabetes lost 8.4% to 12.3% on average, versus 1.7% on placebo.
Has MariTide been studied in humans?
Yes. It has completed Phase 1 and a 592-participant Phase 2 trial, and is now in Phase 3 (the MARITIME program) across several populations.
What side effects have been reported?
Gastrointestinal side effects (nausea, vomiting, diarrhea, constipation) were the most common, similar to other GLP-1 medications, and were reported less often with dose escalation and lower starting doses. No new safety signals were reported through 52 weeks.
Is MariTide approved?
No. It is not approved anywhere and is not sold by any legitimate or grey-market source. Amgen has discussed a possible 2027–2028 filing window, which is not a confirmed timeline.
How often is MariTide injected?
In trials studied so far, MariTide has been dosed subcutaneously every four weeks or every eight weeks. Amgen’s stated goal is a once-monthly, or less frequent, injection schedule.
What remains unknown?
The specific dose or doses moving forward in Phase 3, long-term safety beyond 52 weeks, real-world effectiveness, anti-drug antibody rates, and whether the cardiovascular, kidney, and sleep apnea trials will show benefit are all still unknown.
Bottom line
MariTide is one of the more structurally distinctive compounds in the obesity pipeline: rather than being a peptide that activates GLP-1 and GIP receptors together the way tirzepatide does, it is an antibody-peptide conjugate that blocks GIP while activating GLP-1, built for a roughly three-week half-life and monthly dosing. The strongest evidence behind it is real: a randomized, placebo-controlled, 592-participant Phase 2 trial showing double-digit percentage weight loss in both people with and without type 2 diabetes. What is genuinely published stops there — the specific Phase 3 dosing, long-term safety data, and any regulatory filing are all still pending, and the widely cited 2027–2028 launch window is Amgen’s own stated target, not a confirmed date. It is not approved or sold anywhere, and given its biologic manufacturing process, it is unlikely to surface through grey-market peptide channels the way small synthetic peptides sometimes do.