Is an amylin analogue a GLP-1 drug?

No. Amylin and GLP-1 are different hormones acting at different receptors, though their downstream effects on satiation and gastric emptying overlap. Grouping them as 'GLP-1 drugs' is a common error that makes combination data look like a dose increase when it is not.

Does a 19-day half-life mean it stays active for 19 days?

It means concentration halves in about 19 days. Whether an effect persists depends on where the concentration sits relative to the receptor's response curve, which is not the same question. A drug can remain measurable long after it stops doing anything useful, and can act at concentrations well below its peak.

Why does the compound have three names?

It was MET-233i at Metsera, and became PF-08653945 when Pfizer completed the acquisition on 13 November 2025. It has no INN in circulation yet. Anyone searching the literature needs all three strings, because papers, registry records and press releases use different ones depending on their date.

Is it available as research material?

No. It is investigational, has no widely circulated CAS registration and no established reference standard, and is not supplied on this site.

GLP-1 & Incretin Science

PF-08653945: An Amylin Analogue Built for Monthly Dosing

JMWritten & reviewed by Jack Muncaster · Founder, UK PeptidesLast reviewed 2026-08-234 cited sources

PF-08653945, previously MET-233i, is an investigational amylin analogue with a reported 19-day observed half-life. Phase 1 data showed up to 8.4% placebo-subtracted weight loss at day 36. It is now in Phase 2b alone and combined with berobenatide. It is not licensed anywhere.

Key facts

Development codes: PF-08653945, PF'3945, formerly MET-233i
Class: Amylin analogue
Reported half-life: 19 days (observed, Phase 1)
Phase 1 population: 80 adults with overweight or obesity, without type 2 diabetes
Phase 1 doses: Single 0.15-2.4 mg; multiple 0.15-1.2 mg weekly over five weeks
Phase 1 weight result: Up to 8.4% placebo-subtracted at day 36
Current trial: SOLIS-1 (NCT07575932), Phase 2b
Regulatory status: Investigational; not licensed anywhere

What amylin does, and why it is the second target of choice

Amylin is co-secreted with insulin from pancreatic beta cells and acts largely in the hindbrain, slowing gastric emptying and promoting satiation through pathways that overlap with but are not identical to GLP-1's. Native amylin is a poor drug: it aggregates into amyloid fibrils, which is both a formulation problem and a biological one. Every clinical amylin agonist is therefore an engineered analogue whose primary design constraint is solubility and stability rather than potency. The interest in amylin as a partner for GLP-1 rests on the observation that the two engage overlapping circuits by different routes, so their effects have at least the potential to add rather than merely overlap.

The Phase 1 data, with its limits stated

Metsera reported MET-233i Phase 1 results on 9 June 2025 from a randomised, placebo-controlled, double-blind trial in 80 people with overweight or obesity and without type 2 diabetes. Single doses ran from 0.15 mg to 2.4 mg; the multiple-dose portion gave 0.15 mg to 1.2 mg once weekly over five weeks without titration. Mean placebo-subtracted weight loss reached 8.4% at day 36 after five weekly 1.2 mg doses, with individual responses reported to 10.2%. Gastrointestinal adverse events were described as all mild, dose-dependent and primarily confined to the first week of dosing. This is a Phase 1 study: small, short, and designed to establish safety and pharmacokinetics rather than efficacy. An 8.4% figure over 36 days is not comparable with a 68-week Phase 3 result and should never be placed beside one.

Why the 19-day half-life is the headline number, not the weight loss

A 19-day observed half-life is what makes everything else possible. Dosing interval is governed by how far concentration falls between doses: roughly, an interval of one to two half-lives keeps peak-to-trough variation within a range that a single dose can cover. At 19 days, a monthly interval is about 1.6 half-lives, which is at the edge of workable and explains why the development plan pairs a titration phase with monthly maintenance rather than starting monthly. Compare a peptide with no half-life extension at all, cleared in minutes, and the scale of the engineering becomes clear.

Combinability is a pharmacokinetic property

The stated basis for combining this molecule with berobenatide is that its multiple-dose exposure profile matched that of MET-097i. This is the part that is usually skipped. Two drugs given together in a fixed combination must have compatible concentration-time curves, or the ratio of exposures a patient experiences drifts across the dosing interval - one at trough while the other is near peak. When the interval is a month rather than a day, that drift is large. Matching exposure profiles is therefore a precondition for a fixed monthly combination, and it is an achievement independent of whether the pharmacology combines usefully.

Where it sits among amylin candidates

Cagrilintide is the most advanced, with Phase 3 evidence in combination with semaglutide. Petrelintide is in development as a standalone amylin agonist. Pramlintide is the licensed precedent, approved in the United States as an adjunct in diabetes, and its short duration is precisely what the newer analogues were engineered to fix. PF-08653945 is the least advanced of these and the only one designed from the outset for a monthly schedule. Being latest is not being best; it means the evidence base is thinnest.

Extended research context

The GLP-1 & Incretin Science deep dive

Deep dive: the two routes to a bigger effect

Every compound trying to beat GLP-1 alone has taken one of two routes. The first adds more receptors from the same hormone family — GIP in tirzepatide, GIP and glucagon in retatrutide. The second adds a non-incretin satiety hormone, which in practice means amylin: CagriSema combines cagrilintide with semaglutide, and amycretin engages both receptors from one molecule. Both routes work, because they recruit signalling pathways that do not fully overlap. Neither has escaped the constraint that binds all of them, which is that gastrointestinal tolerability worsens as effect size grows.

Deep dive: why a percentage is not a result

The most-quoted numbers in this field are the least comparable. REDEFINE 1 reported 22.7% and 20.4% for the same compound in the same trial — the first among participants who adhered to treatment, the second across everyone randomised. TRIUMPH-1 reported 28.3% in an uncomplicated obesity population while TRIUMPH-3 reported up to 22.6% in adults with established cardiovascular disease, using the same compound. Before any two figures can be compared they have to match on estimand, population, duration, comparator and whether the number is placebo-adjusted. Most published comparisons match on none of them.

Deep dive: what happens after the trial stops

Every headline figure describes weight while treatment continues. The STEP-1 extension found that a year after semaglutide was stopped, participants had given back roughly two-thirds of what they lost, moving from 17.3% mean reduction to a net 5.6% — though average weight remained below baseline and nearly half stayed at least 5% down. Meta-analysis puts regain at around 0.8 kg per month. This is why maintenance studies such as TRIUMPH-6 matter more to the field's future than another two points of peak reduction.

Research applications

▸Comparing incretin and amylin compounds on a like-for-like basis
▸Interpreting estimands, thresholds and placebo-adjusted figures in trial reports
▸Tracking the obesity pipeline across sponsors and jurisdictions
▸Understanding receptor pharmacology behind GLP-1, GIP, glucagon and amylin
▸Distinguishing licensed medicines from investigational compounds

Handling checklist

✓Identify which estimand a quoted percentage comes from before citing it
✓Check the trial population and baseline BMI against the comparison you are making
✓Confirm the duration and whether the reduction curve had plateaued
✓Read discontinuation rates alongside efficacy figures
✓Verify every NCT identifier against ClinicalTrials.gov rather than secondary reporting

Common research-handling mistakes

Learnt from thousands of researcher orders across our UK labs.

✗ Comparing headline percentages across different trials

Fix: Population, duration, estimand and comparator all differ; the numbers are not interchangeable.

✗ Quoting the larger of two figures from the same trial

Fix: Name the estimand. Efficacy and treatment-policy answer different questions.

✗ Treating peak reduction as a durable outcome

Fix: Substantial regain follows cessation across the class; peak figures describe a maintained state.

✗ Assuming an oral route means a weaker mechanism

Fix: Route and receptor count are independent. Orforglipron is weaker because it hits one receptor, not because it is a tablet.

✗ Reading investigational compounds as available treatments

Fix: Most of this pipeline holds no authorisation anywhere; mazdutide is approved only in China.

Continue researching

Peer-reviewed guides, comparators and matched reference materials.

Frequently asked questions

Is an amylin analogue a GLP-1 drug?: No. Amylin and GLP-1 are different hormones acting at different receptors, though their downstream effects on satiation and gastric emptying overlap. Grouping them as 'GLP-1 drugs' is a common error that makes combination data look like a dose increase when it is not.
Does a 19-day half-life mean it stays active for 19 days?: It means concentration halves in about 19 days. Whether an effect persists depends on where the concentration sits relative to the receptor's response curve, which is not the same question. A drug can remain measurable long after it stops doing anything useful, and can act at concentrations well below its peak.
Why does the compound have three names?: It was MET-233i at Metsera, and became PF-08653945 when Pfizer completed the acquisition on 13 November 2025. It has no INN in circulation yet. Anyone searching the literature needs all three strings, because papers, registry records and press releases use different ones depending on their date.
Is it available as research material?: No. It is investigational, has no widely circulated CAS registration and no established reference standard, and is not supplied on this site.

Primary sources & clinical trials

Peer-reviewed research and registered trials from PubMed, ClinicalTrials.gov, PubChem, FDA and NIH. All links open in a new tab and point to the primary source, so every claim can be verified at origin.

Written and reviewed by

Jack Muncaster · Founder, UK Peptides

Jack founded UK Peptides in Manchester after repeatedly receiving research compounds with missing or recycled paperwork. He is responsible for supplier selection, batch release decisions and the content published in this research library. Every article here is sourced to primary literature and every product page to a signed third-party certificate.

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