MariTide

MariTide is Amgen’s investigational monthly obesity injection: maridebart cafraglutide combines GLP-1 receptor agonism with GIP receptor antagonism, and a 52-week randomized trial found substantial weight loss. MariTide is not FDA-approved, its gastrointestinal side effects can be rough, and Phase 3 must confirm whether slower escalation preserves benefit while improving tolerability.

Key facts: Human RCT evidence · investigational in the U.S. as of July 2026 · studied as a subcutaneous injection every four or eight weeks · common gut side effects · prohibited at all times in tested sport under WADA S0.

What is MariTide?

MariTide is Amgen’s program name for maridebart cafraglutide, a synthetic peptide-antibody conjugate being developed for obesity and related metabolic disease. MariTide is not a registered trade name, and there is no approved product behind the name. Earlier research calls the same molecule AMG 133.

The molecule is bigger and stranger than a standard peptide. A fully human antibody that blocks the GIP receptor carries two GLP-1 agonist peptides, one on each side. The FDA substance record confirms the nonproprietary name, CAS number 2760218-55-9, and UNII Z24U3U73HN, but also warns that a UNII does not imply approval. MariTide belongs in the broader GLP-1 and metabolic peptides hub, with a large investigational asterisk attached.

How does MariTide work, and what is the GIP paradox?

MariTide activates GLP-1 receptors while blocking GIP receptors. GLP-1 activation strengthens the post-meal “enough food” signal and supports glucose-dependent insulin release. GIP blockade is the unresolved half: tirzepatide activates GIP, yet both molecules produce weight loss. One drug presses the GIP switch; the other covers it with tape.

The contradiction is real, but it does not mean either result is fake. Receptor activation can cause later desensitization, while receptor blockade may alter fat biology and food intake through a different route. The Phase 1 paper confirms the designed antagonist and agonist activities in cells and reports weight loss in animals and people. Human trials show the combined molecule works; they do not isolate how much weight loss comes from GIP blockade versus GLP-1 activation. No direct MariTide-versus-tirzepatide trial has settled the argument.

How much MariTide weight loss did the human trial find?

MariTide produced mean weight loss of 12.3% to 16.2% at 52 weeks in adults with obesity but without diabetes, versus 2.5% with placebo, using the treatment-policy analysis that counts all randomized participants regardless of whether they stopped treatment. That is the cleanest headline from the 592-person randomized Phase 2 trial.

The published Phase 2 report also found 8.4% to 12.3% mean loss in the smaller obesity-plus-type-2-diabetes cohort, versus 1.7% with placebo. Claims of “up to 20%” use an efficacy analysis estimating results under continued treatment; they are not invented, but they answer a friendlier question. For a treatment with meaningful discontinuation, the all-participant estimate deserves top billing.

This is human-randomized-trial evidence, not an animal extrapolation. It is still one Phase 2 program funded by Amgen, without cardiovascular-outcome proof or an approved long-term regimen. The evidence is substantial enough to justify Phase 3, not to declare the final product finished.

Is MariTide really a monthly injection?

MariTide was tested every four weeks, but “monthly” describes the trial schedule, not approved instructions. Phase 2 tested 140, 280, or 420 mg every four weeks, plus a 420 mg every-eight-weeks arm and several escalation schedules. Those are study doses for a large biologic, not a do-it-yourself protocol.

The antibody scaffold clears slowly, making fewer injections plausible. The honest catch is equally simple: a long-acting dose also cannot be quickly taken back after nausea or vomiting starts. Dose escalation mattered in Phase 2, with fewer gastrointestinal events when researchers started lower and climbed more slowly. The convenience case is promising; tolerability, final dose, device, and real-world adherence remain Phase 3 questions. There is no legitimate retail MariTide monthly injection in the United States in 2026.

What are the known MariTide side effects and risks?

MariTide side effects were mainly gastrointestinal: nausea, vomiting, diarrhea, and constipation were common, usually mild to moderate, and concentrated around initial dosing. Slower escalation reduced these events. The study reported no unexpected safety signal, but that phrase means no new problem emerged during the trial; it does not create a long-term safety record.

The candidate has no FDA prescribing label, so contraindications, rare-event rates, pregnancy guidance, and post-marketing risks are not established. A monthly molecule also changes the practical risk calculation because exposure persists after an injection. Phase 3 is using a more gradual start partly because tolerability was not a footnote in Phase 2. The side-effects reference explains why duration, severity, and discontinuation matter more than a raw list of symptoms.

Is MariTide FDA-approved or legal in 2026?

MariTide is investigational and not FDA-approved in the United States as of July 16, 2026. Amgen’s own 2026 program update describes maridebart cafraglutide as an investigational therapy in Phase 3. MariTide is therefore not a prescription product, approved compounded substitute, supplement, or registered trade name.

The 2026 WADA Prohibited List creates a separate issue for tested athletes. S0 covers pharmacological substances in clinical development that lack approval for human therapeutic use, making maridebart cafraglutide prohibited at all times while it remains unapproved. Regulatory status and sports status can change independently; both claims are dated here. The wider distinction between approval, access, and online availability is covered in are peptides legal?.

What is Phase 3 MARITIME testing next?

MariTide’s MARITIME-1 and MARITIME-2 trials are testing three dose levels against placebo for 72 weeks, using high-, medium-, and low-dose arms. MARITIME-1 enrolled 3,853 adults with obesity or overweight without type 2 diabetes; MARITIME-2 enrolled 1,105 with type 2 diabetes. Both are active but not recruiting, with primary completion estimated for January 2027.

The MARITIME-1 record and MARITIME-2 record list no results yet. Those trials must show whether the Phase 2 weight loss survives at scale and whether slower escalation makes the monthly format tolerable enough to use. Retatrutide takes the other maximalist route—agonizing GLP-1, GIP, and glucagon—while MariTide blocks one of those same pathways. Obesity pharmacology has reached the useful stage where opposing ideas can finally be tested instead of merely argued.