--- title: "MET-233i | PepTracker Pro" url: https://peptrackerpro.com/peptides/met-233i description: "MET-233i is a first-in-class, once-monthly ultra-long-acting amylin analog for obesity, originally developed by Metsera and now a Pfizer asset. In its Phase 1 trial it produced up to 8.4% placebo-subtracted weight loss after five weekly doses and showed a roughly 19-day half-life - the most durable of any reported amylin analog - supporting once-monthly subcutaneous dosing. It is engineered to be combined with Metsera's monthly GLP-1 agonist MET-097i in a single once-monthly injection." lang: en --- Skip to main content **Educational information only.** This site does not provide medical advice. Read full disclaimer (https://peptrackerpro.com/disclaimer) **Research-only content.** This page is for educational purposes and does not constitute medical advice. Read full disclaimer → (https://peptrackerpro.com/research-disclaimer) # MET-233i Medium Evidence MET-233i is a first-in-class, once-monthly ultra-long-acting amylin analog for obesity, originally developed by Metsera and now a Pfizer asset. In its Phase 1 trial it produced up to 8.4% placebo-subtracted weight loss after five weekly doses and showed a roughly 19-day half-life - the most durable of any reported amylin analog - supporting once-monthly subcutaneous dosing. It is engineered to be combined with Metsera's monthly GLP-1 agonist MET-097i in a single once-monthly injection. Aliases MET233i +6 more Evidence Medium Evidence Last Updated 2026-07-31 Reading Time 5 min ## What It Is MET-233i is an injectable, ultra-long-acting analog of amylin - a pancreatic hormone co-secreted with insulin that promotes satiety, slows gastric emptying and tends to preserve lean mass during weight loss - being developed for obesity. It was created by Metsera using the company's peptide half-life-extension platform and became part of Pfizer's obesity pipeline when Pfizer completed its acquisition of Metsera on November 13, 2025. Amylin has emerged as one of the most clinically validated non-GLP-1 targets in obesity medicine, and most amylin front-runners - cagrilintide, petrelintide and Eli Lilly's selective agonist eloralintide - are peptides given by weekly subcutaneous injection. MET-233i's distinguishing feature is durability: in its Phase 1 study it showed an observed half-life of about 19 days, which Metsera described as the most durable pharmacokinetic profile of any known amylin analog and enough to support once-monthly dosing with simplified or no titration. The Phase 1 trial was a randomized, double-blind, placebo-controlled study in 80 participants with overweight or obesity and without type 2 diabetes, evaluating single subcutaneous doses from 0.15 mg to 2.4 mg and multiple doses from 0.15 mg to 1.2 mg given once weekly for five weeks without titration. Weight loss was dose-dependent, reaching a placebo-subtracted mean of 8.4% at Day 36 after five weekly 1.2 mg doses, with individual responses as high as 10.2%, and the drug was generally well tolerated with no safety signals; most gastrointestinal adverse events were mild, dose-dependent and concentrated in the first week, suggesting rapid tolerance development. The strategic point of MET-233i is combinability. It shares a roughly 19-day half-life with Metsera's ultra-long-acting GLP-1 receptor agonist MET-097i, and its multi-dose exposure profile matched that of MET-097i, supporting a first-in-category once-monthly 'multi-NuSH' (nutrient-stimulated hormone) combination that would pair GLP-1 and amylin biology in a single monthly injection - an infrequent-dosing analog of the injectable GLP-1-plus-amylin combinations CagriSema and MariTide. A 12-week co-administration trial of MET-233i with MET-097i (referred to as MET-233/097) was initiated to test that thesis, with topline data expected around year-end 2025 or early 2026. MET-233i reflects two of 2026's dominant obesity-drug themes: the 'amylin renaissance,' in which lean-mass-sparing amylin mechanisms are pursued as the next pillar beyond GLP-1, and the push toward less frequent, once-monthly dosing to improve adherence. Also known as: MET233i, MET-233, Metsera amylin analog, Pfizer MET-233i, once-monthly amylin analog, MET-233/097 amylin component, ultra-long-acting amylin agonist ## Regulatory Status Investigational Clinical-stage (Phase 1) as of mid-2026; not approved in any jurisdiction. Positive Phase 1 monotherapy data were reported June 9, 2025. A 12-week combination study with the GLP-1 agonist MET-097i (MET-233/097) is ongoing. MET-233i became a Pfizer asset when Pfizer completed its acquisition of Metsera on November 13, 2025. No product is available outside clinical trials; not a compounding-eligible peptide. Effective: 2025 View FDA Source (https://www.globenewswire.com/news-release/2025/06/09/3095726/0/en/Metsera-Announces-Positive-Phase-1-Data-of-First-in-Class-Once-Monthly-Amylin-Candidate-MET-233i.html) ## Why Researchers Study It MET-233i is watched because it tests whether amylin - one of the most validated non-GLP-1 obesity mechanisms, and one prized for sparing lean mass - can be delivered as a durable, once-monthly injection rather than a weekly one. Its roughly 19-day half-life is the longest reported for any amylin analog, and its early weight loss and clean first-week-limited tolerability profile position it as a potential best-in-class amylin backbone. It is also a purpose-built combination partner: engineered to match the half-life and exposure of the monthly GLP-1 agonist MET-097i, it could enable a first-in-category once-monthly GLP-1-plus-amylin injection (MET-233/097), the infrequent-dosing analog of CagriSema and MariTide. As a centerpiece of Pfizer's post-acquisition obesity strategy, it is closely followed by clinicians and investors tracking the 2026 'amylin renaissance' and the move toward monthly dosing. ## Proposed Mechanisms - Agonizes the amylin receptor (calcitonin receptor paired with RAMP proteins) to promote satiety, slow gastric emptying and reduce food intake - Ultra-long-acting peptide engineering gives an observed half-life of about 19 days - the most durable reported for an amylin analog - supporting once-monthly subcutaneous dosing with simplified or no titration - Aims to preserve lean mass during weight loss, a hallmark attributed to amylin-pathway signaling - Matched half-life and exposure with the monthly GLP-1 agonist MET-097i, enabling a co-formulated once-monthly GLP-1-plus-amylin 'multi-NuSH' combination (MET-233/097) - Delivered as a subcutaneous injection rather than an oral small molecule ## Evidence Snapshot Medium Evidence Low Medium High | Study Type | Model | Outcome | Link | | --- | --- | --- | --- | | Clinical (Phase 1, monotherapy) | Randomized, double-blind, placebo-controlled trial in 80 adults with overweight or obesity without type 2 diabetes; single doses 0.15-2.4 mg and multiple doses 0.15-1.2 mg once weekly for 5 weeks without titration | Dose-dependent placebo-subtracted mean weight loss up to 8.4% at Day 36 (five weekly 1.2 mg doses), individual responses up to 10.2%; observed half-life ~19 days; favorable tolerability with no safety signals | Source: https://www.globenewswire.com/news-release/2025/06/09/3095726/0/en/Metsera-Announces-Positive-Phase-1-Data-of-First-in-Class-Once-Monthly-Amylin-Candidate-MET-233i.html | | Clinical (Phase 1, tolerability) | Adverse-event profile in the same Phase 1 trial | Gastrointestinal adverse events were mostly mild, dose-dependent and concentrated in the first week, suggesting rapid tolerance development; no titration required | Source: https://www.biospace.com/press-releases/metsera-announces-positive-phase-1-data-of-first-in-class-once-monthly-amylin-candidate-met-233i | | Clinical / development (combination) | MET-233/097 - 12-week co-administration of MET-233i with the monthly GLP-1 agonist MET-097i | MET-233i's multi-dose exposure matched MET-097i and both share a ~19-day half-life, supporting a first-in-category once-monthly GLP-1-plus-amylin combination; topline data expected around year-end 2025 / early 2026 | Source: https://www.biospace.com/press-releases/metsera-reports-positive-phase-2b-results-for-first-and-best-in-class-ultra-long-acting-glp-1-ra-candidate-met-097i-enabling-rapid-transition-into-phase-3 | | Company / corporate | Pfizer acquisition of Metsera | MET-233i became a Pfizer asset when Pfizer completed its acquisition of Metsera on November 13, 2025, placing the monthly amylin candidate at the center of Pfizer's obesity pipeline alongside MET-097i | Source: https://www.pfizer.com/news/press-release/press-release-detail/pfizer-completes-acquisition-metsera | ## Commonly Discussed Benefits Weight Management: https://peptrackerpro.com/benefits/weight-management Metabolism: https://peptrackerpro.com/benefits/metabolism Fat Loss: https://peptrackerpro.com/benefits/fat-loss Muscle Preservation: https://peptrackerpro.com/benefits/muscle-preservation Researching MET-233i? Track it, set reminders, and keep notes in the free app. Track in App (https://app.peptrackerpro.com/?add=met-233i) ## Safety & Cautions - Early clinical stage - only Phase 1 monotherapy data reported; no Phase 2 or Phase 3 efficacy, durability or long-term safety data yet - The Phase 1 study was short (five weekly doses); month-over-month efficacy and true once-monthly dosing remain to be confirmed in longer trials - Combination (MET-233/097) efficacy and safety in people are not yet established - Human lean-mass benefit and durability of weight loss are unproven - Not FDA-approved, not available outside clinical trials, and not a compounding-eligible peptide - Any 'MET-233i' offered by a vendor is unverified - it is a proprietary investigational peptide ## Comparisons See how MET-233i compares to related peptides: MET-233i vs ALV-200: https://peptrackerpro.com/compare/met-233i-vs-alv-200 MET-233i vs Amycretin: https://peptrackerpro.com/compare/met-233i-vs-amycretin MET-233i vs Cagrilintide: https://peptrackerpro.com/compare/met-233i-vs-cagrilintide MET-233i vs Eloralintide: https://peptrackerpro.com/compare/met-233i-vs-eloralintide MET-233i vs MET-097i: https://peptrackerpro.com/compare/met-233i-vs-met-097i MET-233i vs Petrelintide: https://peptrackerpro.com/compare/met-233i-vs-petrelintide ## Calculator Tools Use our research tools to explore dosing and reconstitution data: Reconstitution Calculator: https://peptrackerpro.com/calculators ## Citations 1. [1] Metsera - Positive Phase 1 Data of First-in-Class Once-Monthly Amylin Candidate MET-233i (Jun 9, 2025) PubMed (https://www.globenewswire.com/news-release/2025/06/09/3095726/0/en/Metsera-Announces-Positive-Phase-1-Data-of-First-in-Class-Once-Monthly-Amylin-Candidate-MET-233i.html) 2. [2] BioSpace - Metsera Announces Positive Phase 1 Data of First-in-Class Once-Monthly Amylin Candidate MET-233i PubMed (https://www.biospace.com/press-releases/metsera-announces-positive-phase-1-data-of-first-in-class-once-monthly-amylin-candidate-met-233i) 3. [3] Metsera - Positive Phase 2b Results for Ultra-Long-Acting GLP-1 RA MET-097i (combination partner context) PubMed (https://www.biospace.com/press-releases/metsera-reports-positive-phase-2b-results-for-first-and-best-in-class-ultra-long-acting-glp-1-ra-candidate-met-097i-enabling-rapid-transition-into-phase-3) 4. [4] Pfizer - Pfizer Completes Acquisition of Metsera (Nov 13, 2025) PubMed (https://www.pfizer.com/news/press-release/press-release-detail/pfizer-completes-acquisition-metsera) ### Keep researching in the app - Log MET-233i to your private tracker - Set a dosing reminder - Compare it side-by-side with your stack Open PepTracker Pro Free: https://app.peptrackerpro.com/?add=met-233i Browse more peptides: https://peptrackerpro.com/peptides ## Related Peptides ### ALV-200 Low Evidence ALV-200 is Alveus Therapeutics' highly selective amylin receptor 3 (AMYR3) peptide agonist in IND-enabling development for obesity, designed to capture amylin's weight-loss and lean-mass-preserving benefits while avoiding the nausea and aversion tied to calcitonin-receptor activation. It is engineered for once-weekly dosing. View Details: https://peptrackerpro.com/peptides/alv-200 \+ Compare: https://peptrackerpro.com/compare?select=alv-200 Track in App: https://app.peptrackerpro.com/?add=alv-200 ### Amycretin Medium Evidence A unimolecular GLP-1 and amylin receptor dual agonist in Phase 3 trials, available in both subcutaneous and oral formulations, with up to 22% weight loss in Phase 1b/2a. Weight Management (https://peptrackerpro.com/benefits/weight-management)Appetite Regulation (https://peptrackerpro.com/benefits/appetite-regulation)Metabolism (https://peptrackerpro.com/benefits/metabolism)Fat Loss (https://peptrackerpro.com/benefits/fat-loss)+1 more View Details: https://peptrackerpro.com/peptides/amycretin \+ Compare: https://peptrackerpro.com/compare?select=amycretin Track in App: https://app.peptrackerpro.com/?add=amycretin ### Cagrilintide High Evidence A long-acting amylin analog studied for appetite regulation; NDA filed for CagriSema (cagrilintide + semaglutide) combination in December 2025, with FDA review expected in 2026. Weight Management: https://peptrackerpro.com/benefits/weight-management Appetite Regulation: https://peptrackerpro.com/benefits/appetite-regulation Metabolism: https://peptrackerpro.com/benefits/metabolism View Details: https://peptrackerpro.com/peptides/cagrilintide \+ Compare: https://peptrackerpro.com/compare?select=cagrilintide Track in App: https://app.peptrackerpro.com/?add=cagrilintide ### Eloralintide Medium Evidence A selective, long-acting amylin receptor agonist in Phase 3 trials for obesity, offering a GLP-1-independent weight loss mechanism with up to 20.1% weight loss in Phase 2. Weight Management: https://peptrackerpro.com/benefits/weight-management Appetite Regulation: https://peptrackerpro.com/benefits/appetite-regulation Metabolism: https://peptrackerpro.com/benefits/metabolism Fat Loss: https://peptrackerpro.com/benefits/fat-loss View Details: https://peptrackerpro.com/peptides/eloralintide \+ Compare: https://peptrackerpro.com/compare?select=eloralintide Track in App: https://app.peptrackerpro.com/?add=eloralintide ### MET-097i Medium Evidence An ultra-long-acting GLP-1 receptor agonist designed for both once-weekly and once-monthly subcutaneous dosing, delivering double-digit weight loss with class-leading gastrointestinal tolerability in mid-stage trials. Weight Management: https://peptrackerpro.com/benefits/weight-management Metabolism: https://peptrackerpro.com/benefits/metabolism Fat Loss: https://peptrackerpro.com/benefits/fat-loss Appetite Regulation: https://peptrackerpro.com/benefits/appetite-regulation View Details: https://peptrackerpro.com/peptides/met-097i \+ Compare: https://peptrackerpro.com/compare?select=met-097i Track in App: https://app.peptrackerpro.com/?add=met-097i ### Petrelintide Medium Evidence A long-acting amylin analog in late-stage clinical development for chronic weight management, designed to deliver double-digit weight loss with a tolerability profile comparable to placebo. View Details: https://peptrackerpro.com/peptides/petrelintide \+ Compare: https://peptrackerpro.com/compare?select=petrelintide Track in App: https://app.peptrackerpro.com/?add=petrelintide ## Structured data ```json [ { "@context": "https://schema.org", "@type": "Organization", "name": "PepTracker Pro", "url": "https://peptrackerpro.com", "logo": "https://peptrackerpro.com/favicon.png", "description": "Evidence-based educational resource dedicated to improving peptide research literacy.", "contactPoint": { "@type": "ContactPoint", "email": "hello@peptrackerpro.com", "contactType": "customer support" }, "sameAs": [] }, { "@context": "https://schema.org", "@type": "MedicalWebPage", "name": "MET-233i", "description": "MET-233i is a first-in-class, once-monthly ultra-long-acting amylin analog for obesity, originally developed by Metsera and now a Pfizer asset. 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