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MariTide: How It Works, Study Results, and Open Questions

Clinical review pending

MariTide explained: antibody–peptide design, phase 1 and phase 2 findings, weight changes, tolerability, and open questions in development.

A balance holds a bead chain on one side and a clear lens on the other.

MariTide, also known as maridebart cafraglutide or AMG 133, is being investigated as a treatment for obesity. It blocks the GIP receptor while activating the GLP-1 receptor. Early human studies show substantial weight loss. Whether that loss can be maintained over the long term, and what risks longer treatment may bring, remain open questions.

MariTide is an experimental compound, not an approved standard treatment. Amgen’s current study website describes its ongoing phase 3 development. Authorized research is the access route documented here; this does not decide the status of every possible special-access route. This article does not replace medical advice, diagnosis, or treatment. Discuss medical decisions and possible study participation with qualified health professionals. Source 1

At a glance

  • MariTide is in phase 3 development; the sources checked here do not establish an FDA-approved routine treatment. The MARITIME program began in 2025.
  • Randomized phase 1 and phase 2 studies have been published. Amgen’s current study website lists MARITIME-1 and -2 as active but no longer recruiting, while other studies are recruiting. Check the status again before contacting a study.
  • Trial registries document individual studies and their criteria.
  • The IUPHAR/BPS Guide to PHARMACOLOGY lists maridebart cafraglutide as ligand 13316.
  • An antibody component blocks GIP receptors, while two attached peptides activate GLP-1 receptors.
  • Phase 2 included 592 adults and several regimens over 52 weeks, not just monthly dosing. Among participants without type 2 diabetes, mean weight loss under the treatment policy approach was 12.3–16.2%, versus 2.5% with placebo: a difference of about 9.8–13.7 percentage points. In phase 1, weight in the highest multiple-dose group remained below baseline for up to 150 days after the last dose. That did not establish unchanged maintenance of the maximum weight loss. Source 1 Source 2 Source 3 Source 4 Source 5

What MariTide is and how it was developed

Origins and molecular design

MariTide grew out of an Amgen research program. Researchers wanted to know whether blocking the GIP receptor could strengthen the weight-reducing effects of GLP-1 receptor activation. This differs from simultaneously activating both receptors.

Killion, Wang, Yie, and colleagues at Amgen Research published foundational preclinical work in Science Translational Medicine in 2018. In that study, antibodies that block the GIP receptor reduced body weight and improved several metabolic measures in mice with diet-induced obesity and in nonhuman primates. Combining the GIPR antibody with a GLP-1 receptor agonist strengthened the effects in the same models. The results supported the idea that the two mechanisms might work better together than either alone. Source 1

The technical challenge was to preserve both activities in a single molecule while achieving a plasma half-life long enough for monthly administration. Half-life is the time it takes for a drug’s concentration in the blood to fall by half. A 2026 paper by Wu and colleagues in the Journal of Medicinal Chemistry describes the development of AMG 133: researchers attached synthetic GLP-1 peptides to IgG-based anti-GIPR antibodies using amino acid linkers. This kept the GLP-1 peptides available in the body much longer than comparable unattached molecules. Source 1

A bispecific structure

MariTide has an unusual design within the GLP-1 field. Most incretin-based medicines or candidates are relatively small peptide analogs, such as semaglutide and tirzepatide, or small molecules, such as orforglipron. MariTide is an antibody–drug conjugate: two GLP-1 receptor agonists are attached by linkers to a full-length monoclonal anti-GIPR antibody of the IgG class, one on each antibody heavy chain.

Véniant, Lu, and colleagues published the foundational characterization of this design in Nature Metabolism in 2024. The paper confirmed activity at both receptors in cell-based assays and described the antibody–peptide structure. It also included weight-loss findings in mice with obesity and cynomolgus monkeys, along with early human phase 1 data. The antibody scaffold gives the molecule a long half-life, allowing monthly subcutaneous injections (under the skin) to be studied. That is a substantially longer interval than the weekly injections used for semaglutide and tirzepatide. Source 1

Dulaglutide provides an earlier example of extending GLP-1 activity by linking it to antibody components. Glaesner and colleagues described this Fc-linked GLP-1 analog in Diabetes/metabolism research and reviews in 2010. The work helped establish a basis for attaching GLP-1 analogs to an antibody scaffold and extending their activity beyond the short lifespan of natural GLP-1. In MariTide, the scaffold has an additional job: blocking a second receptor. Source 1

What GIP does in the body

GIP stands for glucose-dependent insulinotropic polypeptide. It is an incretin hormone whose actions extend well beyond the pancreas. Those varied roles help explain why the consequences of blocking its receptor are not simple to predict.

A 2023 review by Hammoud and Drucker in Nature Reviews Endocrinology explored the different effects of GIP and GLP-1 on fat tissue, the brain, and the cardiovascular system. Drucker is a prominent researcher in incretin biology. The review explains how the two hormones’ signaling pathways differ in the brain and other tissues. Source 1

A 2025 consensus review by Müller and roughly 30 other specialists in Molecular Metabolism summarized GIP’s roles in fat tissue, bone, the central nervous system, and the pancreas. GIP regulates energy balance through diverse actions across multiple target tissues. That biological complexity matters for any therapy that activates or blocks the GIP receptor. Source 1

The GIPR paradox: why blocking GIP might work

The decision to block the GIP receptor is one of the most debated aspects of MariTide. Tirzepatide activates both GIP and GLP-1 receptors and produces substantial weight loss among approved drug treatments. MariTide acts in the opposite direction at GIPR, yet its studies have also reported considerable weight loss. This does not establish equivalence between the two compounds.

The apparent contradiction has prompted extensive debate in incretin research. A 2025 review by Campbell and Drucker in Diabetes revisited the longstanding question of activation versus blockade. It summarized explanations for why both ways of modifying GIPR activity can reduce body weight. Source 1

One possible explanation is receptor desensitization: sustained activation can make a receptor less responsive. In mechanistic experiments published in Nature Communications in 2020, Killion, Chen, Falsey, and colleagues at Amgen showed that prolonged activation reduced GIPR activity in fat cells. This could have metabolic consequences functionally similar to direct blockade. Under this model, chronic activation and direct inhibition can produce comparable downstream states. Source 1

Human genetics provides independent clues about the potential effects of lower GIPR activity. In a 2024 Nature Metabolism study, Kizilkaya and colleagues examined the function of genetic GIPR variants and their associations with traits in large population datasets. Naturally occurring loss-of-function variants were associated with lower BMI. This supports a link between reduced GIP receptor activity and lower body fat, but it does not replace clinical evidence that a drug works. Source 1

A 2024 review by Novikoff and Müller in Trends in Endocrinology and Metabolism brought together preclinical and human findings. It discussed the hypothesis that GIPR blockade could enhance GLP-1 receptor-mediated weight loss by preventing GIP from dampening shared downstream signaling pathways. Source 1

Samms and Sloop argued for GIP receptor activation in Diabetes in 2025. They described favorable effects on pancreatic islets, the central nervous system, and fat tissue. On that basis, they considered activation the better-supported therapeutic direction. Source 1

A 2025 review by Douros, Mowery, and Knerr in the Journal of Clinical Medicine compared the evidence behind both development strategies. It described how activation and blockade can each reduce body weight through different mechanisms. Clear superiority of either approach has not been established. Source 1

The neural circuits involved may help explain the difference. A 2025 Nature Metabolism study in male mice by Gutgesell and colleagues from Müller and Tschöp’s group found that GIPR activation and blockade reduced body weight and food intake through different mechanisms. Even when the two strategies produce similar weight changes in some animal models, they are not necessarily biologically equivalent. Source 1

GIPR in the brain: how blockade might affect food intake

MariTide’s appetite effects probably cannot be explained entirely by actions in fat tissue or the pancreas. A 2024 review by Liskiewicz and Müller in Peptides examined GIPR signaling in the central nervous system. It described GIP receptors in the hypothalamus and hindbrain as important contributors to GIP’s effects on energy balance and body weight. Source 1

A 2025 review by James-Okoro and colleagues in Frontiers in Endocrinology added to this picture. It summarized mechanisms in the hypothalamus and hindbrain through which changes in GIPR activity can influence food intake, connecting receptor activity with eating behavior. Source 1

At the level of individual nerve cell groups, Adriaenssens and colleagues identified distinct populations of GIPR-expressing neurons in the hypothalamus and brainstem in JCI Insight in 2023. These populations perform different functions in food-intake regulation. The findings point to effects in specific appetite-regulating nuclei rather than a nonspecific effect throughout the brain. Source 1

Together, these studies provide a biological basis for the hypothesis that MariTide’s GIPR-blocking component affects central appetite circuits as well as peripheral metabolism. By themselves, however, they do not establish how much this mechanism explains MariTide’s effects in humans.

What human studies show

Phase 1: weight loss after the last dose

The first human phase 1 results appeared alongside the preclinical mechanistic findings in Véniant, Lu, and colleagues’ 2024 Nature Metabolism paper. Source 1

The phase 1 trial, NCT04478708, was randomized, double-blind, and placebo-controlled. Participants were adults ages 18–65 with obesity and without diabetes. It tested single and repeated ascending doses. Single doses ranged from 21 mg to 840 mg, and multiple-dose regimens were also studied.

At the highest repeated dose, 420 mg every four weeks, mean weight fell by 14.5% by day 85. In contrast, the placebo group gained 1.5%; the earlier description of weight loss with placebo was incorrect. At 140 mg every four weeks, weight loss after three doses was about 7.4% on day 78. Source 1

After three administrations, weight remained reduced in every multiple-dose group for 70 days after the third dose. In the 420-mg group, it was still as much as 11.2% below baseline 150 days after the final administration. This does not mean the maximum 14.5% reduction was maintained unchanged. The finding is interesting given weight regain after stopping semaglutide or tirzepatide, but the study did not directly compare those drugs. Source 1

Adverse events were mostly mild, temporary gastrointestinal symptoms such as nausea and vomiting. They generally resolved within about 48 hours of administration. The report did not describe treatment-emergent serious events or adverse events leading to permanent discontinuation. The small phase 1 sample and short study duration limit how widely these findings can be applied.

Researchers are still investigating why the effects persisted after the last dose. Possible explanations include the long pharmacokinetic half-life, longer-lasting receptor or central nervous system adaptations, or a combination of these factors. Greenhill highlighted the signal in a 2024 research commentary in Nature Reviews Endocrinology, particularly in the context of weight regain after stopping GLP-1 receptor agonists. Source 1

Phase 2: efficacy in 592 adults

Jastreboff, Ryan, Bays, Ebeling, and colleagues published the phase 2 results online on June 23, 2025; the New England Journal of Medicine issue appeared on September 4. The study randomized 592 adults in two cohorts for 52 weeks: 465 with obesity without type 2 diabetes and 127 with obesity and type 2 diabetes. The first cohort had seven arms, allocated in a 3:3:3:2:2:2:3 ratio: 140, 280, or 420 mg every four weeks without dose escalation; 420 mg every eight weeks; 420 mg every four weeks with either four-week or twelve-week dose escalation; and placebo. The incomplete group counts previously given did not reliably account for the 465 participants. Source 1

Under the treatment policy approach, which considers outcomes regardless of whether assigned treatment continues, mean weight change at 52 weeks ranged from −12.3% (95% confidence interval, −15.0 to −9.7%) to −16.2% (−18.9 to −13.5%). With placebo, it was −2.5% (−4.2 to −0.7%). This corresponds to a difference of about 9.8–13.7 percentage points; the active-treatment values are not already placebo-adjusted. The range covers the regimens studied, including the eight-week interval and dose-escalation arms. A confidence interval describes uncertainty around an estimate, not the range of individual outcomes. A different analysis assuming continued treatment can yield different figures and should not be mixed with this one.

By week 52, weight loss in the studied dose groups had not reached a plateau, or an apparently stable endpoint. Further loss beyond the study period therefore seemed possible, but this observation did not demonstrate it.

The 127 participants with type 2 diabetes were assigned in a 1:1:1:1 ratio to 140, 280, or 420 mg every four weeks without dose escalation, or placebo. Under the treatment policy approach, mean weight changes ranged from −8.4% (95% confidence interval, −11.0 to −5.7%) to −12.3% (−15.3 to −9.2%), versus −1.7% (−2.9 to −0.6%) with placebo. The difference was therefore about 6.7–10.6 percentage points. Exact group sizes cannot be inferred from the allocation ratio alone.

HbA1c also fell by 1.2–1.6 percentage points, while rising by 0.1 percentage points with placebo. HbA1c reflects average blood glucose exposure over preceding weeks to months. This improvement fits the established mechanism of GLP-1 receptor activation: increasing glucose-dependent insulin release and reducing glucagon release. The small number of participants per diabetes treatment arm limits the precision of the estimates. These findings come from the phase 2 publication. Source 1

Gastrointestinal symptoms such as nausea, vomiting, and constipation were among the common adverse events. The study report described fewer such events with dose escalation and a lower starting dose. Amgen also reported treatment discontinuations because of gastrointestinal events: up to 7.8% in the dose-escalation arms, lower than in arms without escalation. Predominantly mild or moderate symptoms can still be important to the people experiencing them. Source 1

The phase 2 study prompted letters from Liu and from Muskiet and Smits, followed by a response from Jastreboff, Ryan, and Pannacciulli. The bibliographic records confirm this scientific correspondence. Without checking the complete letters, this article does not attribute a particular criticism of individual safety or efficacy outcomes to them. Publication of correspondence alone does not invalidate the primary findings. Source 1 Source 2 Source 3

How the results fit among incretin-based treatments

The roughly 12–16% weight loss reported at 52 weeks in phase 2 participants with obesity without diabetes falls within a range also seen in GLP-1 monotherapy studies. At some doses, it approaches results reported for tirzepatide. These are changes within the MariTide treatment groups; subtracting the weight loss in the placebo group yields a smaller effect.

For context, the phase 3 STEP 1 trial by Wilding, Batterham, and colleagues, published in the New England Journal of Medicine in 2021, assigned 1,961 adults with overweight or obesity without diabetes in a 2:1 ratio to weekly 2.4-mg semaglutide or placebo. At 68 weeks, mean weight loss was about 14.9% with semaglutide and 2.4% with placebo. The difference was statistically significant, with P < .001. Source 1

The phase 3 SURMOUNT-1 trial of tirzepatide, published by Jastreboff, Aronne, Ahmad, and colleagues in the New England Journal of Medicine in 2022, included 2,539 adults with obesity or overweight and a coexisting condition. At 72 weeks, mean weight loss was about 15.0%, 19.5%, and 20.9% with weekly doses of 5, 10, and 15 mg, respectively, versus 3.1% with placebo. For every dose, P was < .001 versus placebo. Source 1

In the phase 2 study of retatrutide, a triple GLP-1/GIP/glucagon receptor agonist, Jastreboff, Kaplan, Frías, and colleagues reported weight loss of up to 24.2% at 48 weeks with the highest tested dose in the New England Journal of Medicine in 2023. Source 1

These figures permit only limited comparisons. Study designs, populations, treatment durations, and dosing strategies differ. They provide scientific context, not a reliable ranking of the compounds. Approval status and the extent of available evidence also differ substantially.

A 2026 review by Son and colleagues in Endocrine Reviews placed new GLP-1-based medicines in the development of the next generation of obesity drug treatments. These include dual agonists, triple agonists, and antibody conjugates such as MariTide. Source 1

A practical feature of MariTide is its monthly dosing interval. Weekly injections under the skin can be a burden during long-term treatment. Whether monthly administration improves adherence and real-world outcomes remains an important question for further clinical development.

FDA status and clinical development

The Amgen study website checked here continues to describe MariTide as an investigational medicine in the phase 3 MARITIME program. It does not establish an FDA-approved routine indication. A registry listing or authorization to conduct a clinical study is not marketing approval. This is a dated assessment as of October 31, 2026, not a comprehensive review of every regulatory proceeding worldwide. Source 1

Amgen began the MARITIME program in 2025 with studies of obesity with and without type 2 diabetes and related cardiometabolic conditions. These include MARITIME-1 and the cardiovascular outcomes trial MARITIME-CV. Amgen’s current program website lists MARITIME-1 and -2 as active but not recruiting; MARITIME-CV, -HF, and -OSA are listed as recruiting. Locations and enrollment availability need current confirmation from each study team. Source 1 Source 2 Source 3

An ordinary prescription or a “compounded” label does not establish approved access to MariTide. The FDA explains that biological products are not eligible for the compounding exemptions in sections 503A or 503B. Its separate policy on mixing, diluting, or repackaging certain biologics is not general permission to market an unapproved antibody–peptide conjugate as a compounded product. This does not claim that every conceivable authorized research or special-access route is excluded. Source 1

What would be needed for MariTide to become available?

For FDA approval and routine prescribing, Amgen would need to submit an appropriate application supported by completed phase 3 data from the MARITIME program. The FDA would then need to review and approve it.

The overall timeline depends on recruitment, follow-up, analysis, manufacturing evidence, and regulatory review. General figures such as two to five years for phase 3, or six versus ten to twelve months for different review processes, are not a confirmed schedule for this compound and are not used here as a forecast.

A study’s start date does not establish a reliable approval year. The earlier suggestion that approval “before approximately 2028” would be optimistic was not an agency-confirmed prediction. Whether, when, and for which indication approval might be granted depends on the evidence and review. Authorized trial participation is a documented research route; other possible access pathways would need separate assessment.

What this means in practice

For products advertised online or through unofficial channels as MariTide, AMG 133, or maridebart cafraglutide, the name alone says nothing about verified identity, purity, or potency. MariTide is a proprietary Amgen development. The online products described are not established as FDA-reviewed or approved preparations.

ClinicalTrials.gov provides information about MARITIME and related studies, including their recruitment status and contact details. Source 1

Tirzepatide, sold under the brand names Mounjaro and Zepbound, offers a useful mechanistic comparison: it is an approved compound that activates both GIP and GLP-1 receptors. This comparison does not require a claim that it remains the only approved GIP-related drug everywhere at every later point in time.

Tirzepatide activates the GIP receptor, while MariTide blocks it. Both approaches have produced meaningful weight loss in their respective studies. The existing clinical evidence does not show which mechanism is superior. Debate also continues in the scientific literature: Lilly researchers argue for activation, while independent groups have found that activation and blockade can reduce body weight through different neural circuits.

A direct preclinical comparison by Davies, Turland, Tran, and colleagues in male mice, published in Diabetes, Obesity and Metabolism in 2026, reported metabolic benefits from both GIPR activation and blockade, although the patterns differed. This animal comparison adds scientific context. For clinical use, development stage matters: tirzepatide is an approved prescription drug with an established clinical evidence base; MariTide remains experimental without an approved indication established here. Source 1

Weight changes after treatment ends also matter when interpreting MariTide’s findings. Studies of approved drugs have documented substantial regain after withdrawal. In the STEP 1 extension, published by Wilding, Batterham, Davies, and colleagues in 2022, participants regained an average of about two-thirds of their previous weight loss during the year after stopping semaglutide. Source 1

The SURMOUNT-4 study by Aronne, Sattar, Horn, and colleagues, published in JAMA in 2024, likewise found considerable weight regain in participants who stopped tirzepatide after an initial 36-week treatment period. Continuing treatment maintained weight loss much more effectively than switching to placebo. Source 1

In phase 1, weight in the highest MariTide multiple-dose group remained reduced for up to 150 days after the last dose, ending as much as 11.2% below baseline. The maximum weight loss was therefore not maintained completely unchanged. Without a direct comparison, this does not establish an advantage over weekly GLP-1 receptor agonists. Source 1

A 2026 review by Shah and colleagues in Diabetes, Obesity and Metabolism addressed the clinical management of weight regain and cardiometabolic consequences after discontinuing GLP-1 receptor agonists. Long-term treatment planning is a clinical issue in its own right. Whether MariTide’s persistence after the last dose offers a practically important advantage in larger phase 3 populations still needs confirmation in the MARITIME program. Source 1

Safety: what is known and what remains uncertain

Phase 1 and phase 2 safety findings

The side-effect profile described in phase 1 and phase 2 largely resembles known effects of GLP-1 receptor activation. Gastrointestinal symptoms, including nausea, vomiting, and constipation, were most common. These symptoms are dose-related. Gradual dose escalation is intended to improve tolerability by allowing adjustment to increasing GLP-1 receptor activity.

The phase 2 report described no unexpected safety signals. That is narrower than saying there were no serious events or that safety was fully established. Gastrointestinal symptoms caused some participants to discontinue treatment, and their frequency depended on the regimen. A study of this size cannot adequately characterize rare or longer-term risks. Source 1

A 2026 review in Metabolism Open on multireceptor agonists and novel metabolic modulators is cited for the observation that gastrointestinal events in the published MariTide studies were predominantly mild or moderate. Source 1

What remains unknown

Long-term safety data in large populations are not yet available in the evidence described here. Phase 2 studies assess efficacy and look for safety signals; they cannot characterize a drug’s complete long-term risk profile. A fuller assessment of cardiovascular outcomes, possible effects on bone and kidney function, and cancer risk requires phase 3 data and, if approval follows, potentially postmarketing monitoring.

The antibody component also raises questions typical of biologic medicines, including immunogenicity: the body might form antibodies against the therapeutic antibody. This has been monitored in studies but requires longer follow-up for a fuller interpretation.

Some approved GLP-1-based products carry an FDA warning about thyroid C-cell tumors. The Wegovy prescribing information checked here refers to semaglutide findings in rodents and uncertain relevance to humans. This is relevant research context, but it is not a MariTide-specific finding or approved warning label for MariTide. Another medicine’s warnings or contraindications should not be transferred unchanged to the investigational compound. Source 1

Anyone considering participation needs the current information and consent documents for the particular MARITIME trial. These explain the known and possible risks for that study.

Who should not use MariTide?

The evidence described here does not support self-directed MariTide use. It is an experimental antibody–peptide conjugate developed by Amgen. These sources do not establish an approved routine treatment. Research access, or another potentially authorized clinical route, requires the conditions applicable to that route to be met.

The following groups raise particular clinical or theoretical safety questions. This is not presented as a verified, complete exclusion list for every MARITIME study. The individual protocol and study team determine eligibility; this is not an approved MariTide contraindication list:

  • A personal or family history of medullary thyroid carcinoma, or multiple endocrine neoplasia type 2 (MEN 2), makes rodent thyroid C-cell findings associated with GLP-1 receptor agonists relevant to the assessment.

  • Active cancer, particularly tumors expressing GLP-1 or GIP receptors, raises the theoretical question of whether changes in receptor activity could affect tumor biology. This does not establish clinical harm caused by MariTide.

  • Severe or uncontrolled gastroparesis already involves delayed stomach emptying. GLP-1 receptor activation further slows gastric movement.

  • Previous severe hypersensitivity reactions to biologic medicines warrant consideration because of the antibody–peptide structure.

  • Safety during pregnancy or breastfeeding cannot be established from these data. Drug-induced weight loss is not indicated during pregnancy.

  • Pharmacokinetic information in severe kidney or liver impairment is described as limited. How the body absorbs, distributes, and clears the compound in these groups is therefore incompletely characterized.

The study team determines eligibility using the trial’s inclusion and exclusion criteria. Official study information is available through ClinicalTrials.gov. Source 1

What the findings mean

MariTide takes a novel approach within incretin-based treatment. Its antibody–peptide structure, monthly or less frequent regimens, and GIP receptor blockade distinguish it from approved GLP-1 therapies. The phase 1 finding of weight remaining reduced for 150 days after the last dose in the highest multiple-dose group is interesting. It establishes neither unchanged maintenance of peak weight loss nor superiority over weekly drugs.

The phase 2 trial of 592 participants showed substantial weight loss over 52 weeks. Common side effects were gastrointestinal symptoms, which also caused discontinuations. The ongoing MARITIME program is intended to assess efficacy and safety in larger groups. Superiority over approved treatments can only be assessed through comparisons designed to answer that question; not every phase 3 study does so. According to the sources checked here, MariTide remains investigational.

Important safety information

MariTide is an experimental Amgen compound being studied in phase 3. The sources checked do not establish an FDA-approved routine treatment. This statement is not a comprehensive review of approval status in every country.

The FDA says biological products are not eligible for the compounded-drug exemptions in sections 503A or 503B. A separate policy concerning the mixing or repackaging of certain biologics is not general permission to market a compounded MariTide product. This article provides information, not individual medical or legal advice. Source 1

The evidence described does not establish MariTide as routinely available by prescription or as a lawfully prepared compounded product. Online products labeled MariTide, AMG 133, or maridebart cafraglutide do not gain FDA approval or verified identity, purity, or potency from those names.

Rodent thyroid C-cell findings for individual approved GLP-1 products provide research and safety context; they do not establish a MariTide-specific tumor effect here. Their relevance to humans is uncertain. Nausea, vomiting, constipation, and other gastrointestinal symptoms can be burdensome. MariTide trials apply their own criteria, including when assessing a personal or family history of medullary thyroid carcinoma or MEN 2.

These data do not support self-administration. Regulated research or another lawfully authorized route has its own requirements; this is not a blanket claim that every possible access route is prohibited. Particular assessment questions arise with medullary thyroid carcinoma or MEN 2, active cancer, severe gastroparesis, previous severe hypersensitivity to biologics, pregnancy or breastfeeding, and severe kidney or liver impairment. This is not an approved contraindication list.

Common adverse events in phases 1 and 2 included nausea, vomiting, and constipation, consistent with known effects of GLP-1 receptor agonists. Long-term safety data in large populations are not available in the evidence described here.

Extension studies have documented weight regain after stopping approved GLP-1-based treatments. MariTide’s early finding of weight remaining reduced after the last dose does not establish permanent weight maintenance without treatment or provide a direct comparison with those drugs.

Detailed information about the investigational medicine is provided during the information and consent process for each MARITIME study. Trials can be found through ClinicalTrials.gov. Source 1

Frequently asked questions

Is MariTide FDA-approved?

The sources checked here describe MariTide, also called maridebart cafraglutide or AMG 133, as experimental and in phase 3 development. They do not establish an FDA-approved routine indication. Amgen’s study website distinguishes active studies that are no longer recruiting from programs still accepting participants. A registry listing is not approval. Source 1

How does MariTide differ from tirzepatide?

Both compounds act at the GIP receptor, but in opposite directions: tirzepatide is a GIP receptor agonist that activates it, while MariTide is a GIP receptor antagonist that blocks it. Both also activate GLP-1 receptors.

The clinical evidence so far suggests that both approaches can produce substantial weight loss. This assessment is not based on a direct clinical comparison. Tirzepatide has completed phase 3 trials and FDA approval; MariTide does not yet have those demonstrated outcomes. The comparison therefore provides scientific context, with substantial differences in approval status and the amount of evidence.

How much weight loss did MariTide produce in clinical studies?

The phase 2 study included 465 adults with obesity without type 2 diabetes in seven arms. Under the treatment policy approach, mean weight loss at 52 weeks ranged from 12.3% to 16.2% depending on the regimen, versus 2.5% with placebo. The difference was about 9.8–13.7 percentage points. Regimens included four- and eight-week intervals and dose escalation; these figures are not solely the results of fixed monthly doses. Source 1

The cohort with obesity and type 2 diabetes included 127 adults. Weight loss in the active-treatment groups was about 8.4–12.3%, versus 1.7% with placebo, a difference of 6.7–10.6 percentage points. Individual outcomes varied. The dose groups had not shown a weight-loss plateau by week 52.

Phase 3 data from MARITIME are needed to confirm how durable these results are and how widely they apply to other clinical settings.

Why is monthly MariTide being studied when other GLP-1 drugs are injected weekly?

The monthly interval is related to the antibody scaffold. IgG antibodies typically have a plasma half-life of several weeks in humans. Attaching GLP-1 peptides to an antibody can keep them in the body much longer than unattached analogs.

Wu and colleagues’ 2026 paper in the Journal of Medicinal Chemistry describes a design intended for monthly or even less frequent dosing. Fewer injections could make regular treatment easier in a chronic condition such as obesity. Whether they actually improve adherence requires clinical study. Source 1

What is the MARITIME clinical trial program?

MARITIME is Amgen’s phase 3 program for maridebart cafraglutide, launched in 2025. It includes several studies in people with obesity, with and without type 2 diabetes, and related cardiometabolic conditions.

Phase 3 trials are intended to confirm efficacy in larger populations, provide longer-term safety information, and support an FDA application. Registry entries provide study locations and recruitment information, including the MARITIME-1 entry on ClinicalTrials.gov. Source 1

What is the difference between AMG 133, MariTide, and maridebart cafraglutide?

All three names refer to the same compound but are used in different development and communication contexts. AMG 133 is Amgen’s internal development code. Maridebart cafraglutide is the international nonproprietary name, or INN. MariTide is a shortened name used in reporting and in this article.

Each refers to the same bispecific antibody–peptide conjugate that combines GIPR blockade with GLP-1 receptor activation.

Is MariTide available as a compounded preparation?

A lawful compounded MariTide product is not established here. The FDA explains that biological products are not eligible for the compounding exemptions under sections 503A and 503B. Its separate policy on mixing, diluting, or repackaging certain biologics is not general permission to market an unapproved antibody–peptide conjugate. Source 1

Products sold online or through unofficial channels as MariTide, AMG 133, or maridebart cafraglutide are not thereby FDA-approved or of verified quality. The complex antibody–peptide structure cannot be recreated through ordinary compounding procedures. Obtaining material outside clinical trials can carry substantial risks.

Could MariTide become available by prescription in the future?

It could, if the MARITIME phase 3 studies provide adequate efficacy and safety evidence and an appropriate approval application submitted by Amgen is successfully reviewed.

A date cannot be predicted reliably. Completing phase 3 trials, analyzing the data, and FDA review generally take years. The September 2026 information described in the source did not include an announced approval date.

This article is for information. According to the sources checked, MariTide is experimental; an approved routine FDA therapy is not established. An authorized trial is a documented research access route, not an instruction for self-treatment. Consult qualified health professionals about individual medical questions.

References