Maridebart Cafraglutide

Maridebart cafraglutide, branded MariTide and known internally as AMG 133, is Amgen's investigational monthly injection for obesity now in Phase 3 development. It combines GLP-1 receptor activation with GIP receptor blockade as a peptide-antibody conjugate, a mechanism that runs opposite to Lilly's tirzepatide, which activates both receptors. The peptide-antibody format is what makes once-monthly dosing feasible: attaching the peptide agonist to an antibody backbone extends the half-life to roughly a month. Phase 2 data published in the New England Journal of Medicine in 2025 [1] showed mean weight loss of 12 to 16 percent at 52 weeks by intent-to-treat, and up to approximately 20 percent when excluding early dropouts, on par with the tirzepatide and semaglutide bar. But higher-than-hoped gastrointestinal adverse events (vomiting rates up to the 90 percent range and treatment discontinuation up to 27 percent in fixed-dose arms without titration) triggered a sharp stock selloff after the November 2024 topline release. Amgen has since pushed a broad Phase 3 program covering obesity, obesity plus type 2 diabetes, heart failure with preserved ejection fraction (HFpEF), and obstructive sleep apnea, with a revised dose-titration schedule intended to blunt GI intolerance. The commercial stakes are substantial. Novo Nordisk's Wegovy and Lilly's Zepbound already dominate a market projected to exceed $100B by 2030 [12][13], and Amgen needs to differentiate on monthly convenience or absolute weight loss to take share. The MARITIME-1 obesity readout is Amgen's most important 2026 catalyst outside its oncology franchise.

Novel compound with no prior approval anywhere. The Phase 3 MARITIME program is fully active with multiple parallel trials. NCT06858839 [3] is the flagship obesity study in adults without type 2 diabetes, n=3,853, currently ACTIVE_NOT_RECRUITING (meaning enrollment is complete and patients are being followed to the primary endpoint) with a 72-week body weight change primary endpoint. NCT07037459 [4] targets heart failure with preserved or mildly reduced ejection fraction in obese patients, n=5,056, recruiting, with a composite cardiovascular death or heart failure event endpoint. NCT07225686 [5] addresses obstructive sleep apnea in patients on positive airway pressure therapy, n=250, with apnea-hypopnea index (AHI, a count of breathing pauses or shallow-breathing events per hour of sleep) change at 52 weeks. NCT06660173 [6] is the Phase 2 T2D bridge, n=409, with HbA1c (a blood test reflecting average blood sugar over the prior three months) at 24 weeks. MARITIME-1 extension NCT07684235 [7] captures long-term safety and efficacy. No FDA Breakthrough Therapy or Fast Track designation has been disclosed publicly for MariTide, which is unusual for a program of this profile but not disqualifying. Amgen has publicly guided MARITIME-1 topline for 2026, most likely late in the year based on the trial's active-not-recruiting status and 72-week follow-up. Regulatory submission is contingent on positive readout, with a plausible BLA (Biologics License Application, the FDA submission pathway for complex biological medicines) filing in 2027 and potential launch in 2028. The DB anchor trial (NCT07229157) is a Phase 1 thorough-QT cardiac safety study, not representative of the program's development stage.

Two gut-derived hormones govern appetite and blood-sugar signaling: GLP-1 and GIP. GLP-1 tells the brain you are full and slows how fast the stomach empties. GIP was originally thought to promote fat storage after meals. Then Lilly's tirzepatide, which activates both GLP-1 and GIP receptors, beat semaglutide (GLP-1 alone) on weight loss in a head-to-head trial [14]. That result suggested GIP activation helps. Amgen bet the opposite way. Their hypothesis: chronic GIP receptor activation causes the receptor to desensitize (like a thermostat that stops responding), and blocking the receptor entirely might work better. Preclinical work in Nature Metabolism [2] showed the antagonist strategy produced weight loss and metabolic improvements in animals and Phase 1 humans. Phase 2 in NEJM 2025 [1] confirmed the effect in obese patients over 52 weeks. Whether GIP antagonism actually outperforms GIP agonism cannot be answered without a direct head-to-head trial, and none is planned. Both mechanisms clearly work for weight loss; the biology of why is still debated. The peptide-antibody conjugate architecture is a half-life engineering strategy: linking the peptide to an antibody Fc region extends serum half-life from roughly one week (semaglutide, tirzepatide, which are dosed weekly) to approximately four weeks, allowing monthly rather than weekly dosing.

Flagship trial NCT06858839 [3] evaluates MariTide versus placebo in adults with obesity or overweight (no type 2 diabetes) over 72 weeks, primary endpoint percent body weight change from baseline. Enrollment target 3,853, status ACTIVE_NOT_RECRUITING. The comparator is placebo, not semaglutide or tirzepatide. That is the standard regulatory design and mirrors what Novo and Lilly ran to win obesity labels, but it leaves the head-to-head question unanswered and forces cross-trial comparison, which payers and physicians will do anyway. Phase 3 also uses a revised dose-titration schedule (slower stepwise dose escalation) informed by Phase 2 tolerability findings, where fixed dosing without escalation produced high vomiting and discontinuation rates while dose-escalation arms brought GI discontinuation to single digits. HFpEF outcomes trial NCT07037459 [4] uses a hard composite (CV death or HF events) in 5,056 obese patients with HFpEF, following the Novo STEP-HFpEF template that established semaglutide's cardiovascular label expansion [8]. The size and endpoint choice signal Amgen is aiming for a cardiovascular indication, not just weight loss. OSA trial NCT07225686 [5] uses apnea-hypopnea index at 52 weeks in 250 patients, mimicking Lilly's SURMOUNT-OSA design that won Zepbound its sleep apnea label [9]. T2D trial NCT06660173 [6] is Phase 2 rather than Phase 3, so a separate diabetes registration study will likely follow. The portfolio is well-scoped to the modern obesity playbook: weight-loss primary, then indication-specific outcomes trials to expand payer coverage.

Our model estimates a 45% chance this drug is eventually approved. It starts from the historical base rate for Phase 3 drugs in this area (about 66%), then adjusts using ten facts about the trial and sponsor. What moves the number most: it is helped by more secondary endpoints than usual and the sponsor's strong record of getting drugs approved; it is held back by weak or limited earlier-phase results and smaller-than-typical enrollment for this phase. The other facts land near average for this stage, so they leave the estimate roughly where the base rate put it.

Efficacy: Phase 2 showed 12 to 16 percent intent-to-treat mean weight loss at 52 weeks (up to ~20 percent excluding dropouts), and 72-week durability is what matters for Phase 3. If MariTide lands below 20 percent mean weight loss on the Phase 3 primary, it becomes a follower drug rather than a share-taker versus tirzepatide's SURMOUNT numbers. Safety: GI tolerability drove the November 2024 stock reaction. Phase 2 reported vomiting rates as high as ~92 percent in the fixed 420 mg every-8-weeks obesity arm (no dose escalation) and as low as ~43 percent in a 4-week dose-escalation cohort; treatment discontinuation from GI adverse events was 12 to 27 percent in fixed-dose arms without escalation, versus up to ~7.8 percent in dose-escalation arms [1]. Nausea and vomiting episodes were mostly mild-to-moderate, first-dose weighted, and resolved within days. Amgen carried the dose-escalation approach into Phase 3, so Phase 3 tolerability should look meaningfully better than the worst Phase 2 arms, but the market will still compare Phase 3 discontinuation head-to-head against the semaglutide and tirzepatide baselines. A bone mineral density signal appeared in Phase 2 subgroup analyses [1] and needs to resolve with longer-duration Phase 3 exposure. Execution: the Phase 3 program spans more than 12,000 patients across trials, an expensive commitment. Enrollment status suggests Amgen is executing on obesity, but the HFpEF outcomes trial [4] recruiting a specific comorbid population can slow. Supply and manufacturing: Novo and Lilly hit multi-year supply constraints on their GLP-1 franchises, and Amgen has not publicly disclosed dedicated MariTide manufacturing capacity or expansion plans; this is a watch item ahead of launch. IP: specific composition-of-matter expiry for maridebart cafraglutide has not been publicly detailed by Amgen, but the compound is protected by post-2020 filings that would ordinarily provide ~20 years of nominal patent life absent generic biosimilar challenge; Amgen has not disclosed detail in public filings. Commercial: Novo and Lilly own the market. Wegovy generated approximately $8.4B in 2024 (DKK 58.2B) [12], and Lilly's Mounjaro plus Zepbound combined for over $16B in 2024 [13]. Monthly dosing is Amgen's differentiator, but Lilly's oral orforglipron and Novo's amycretin (an investigational amylin/GLP-1 receptor co-agonist in both oral and subcutaneous formats) are advancing, and oral is a bigger convenience wedge than monthly injectable. Payers will demand meaningful clinical or price differentiation before granting formulary access to a fourth entrant.

Worth watching. MARITIME-1 topline is one of the highest-signal readouts of 2026, ranking with Lilly's retatrutide Phase 3 and Novo's follow-on programs as the top obesity events of the year. Three data points make MariTide a signal versus noise. First: mean percent body weight loss at 72 weeks. Phase 2 landed at 12 to 16 percent ITT and ~20 percent completer-analysis at 52 weeks [1], so Phase 3 has already approximately cleared the competitive bar in a smaller trial. The question is whether the larger, longer Phase 3 replicates the ~20 percent figure. Twenty percent or better on the Phase 3 primary is competitive; below that is second tier. Second: adverse-event-driven discontinuation rate. Phase 2 saw 12 to 27 percent discontinuation in fixed-dose arms and as low as ~7.8 percent in dose-escalation arms; Phase 3 uses the revised titration schedule, so a Phase 3 discontinuation rate under 10 percent would ease the tolerability concern that hit the stock in November 2024, and higher would let the market re-price. Third: updated bone density language in the primary readout, which will determine whether FDA and payers view a chronic-use liability. Amgen's 2025 revenue was approximately $36.8B per the 2025 10-K filing [11], so the company has both the balance sheet to launch commercially and a diversified franchise such that a MariTide miss would not be existential. Check back in Q3-Q4 2026 for MARITIME-1 topline. HFpEF and OSA readouts likely follow in 2027. If topline is clean, expect BLA filing in 2027 and approval in mid-2028. AMGN stock will move on the topline; option positioning tightens meaningfully in the two months prior.