What is retatrutide's CAS number?

2381089-83-2 is the number commonly listed, though it does not resolve to a PubChem record.

Why is there no PubChem entry?

Not clear. Searches under the name, the development code and the CAS all return nothing, which is unusual for a compound at this stage of development.

Is CID 156588324 retatrutide?

No. That record is tirzepatide, its synonyms include Zepbound and LY3298176. It was cited in error here and has been removed.

Retatrutide CAS Number and Chemical Identity

The short answer

Retatrutide is commonly listed under CAS 2381089-83-2 with a molecular weight near 4,731 Da. Neither resolves to a PubChem record. Searches for retatrutide, LY3437943 and the CAS all return nothing. The identifiers come from supplier and reference sources rather than a primary database.

Key facts

Development code: LY3437943
Reported CAS: 2381089-83-2 (no PubChem record)
Reported MW: ~4,731.33 Da
Reported formula: C221H342N46O68 (sources disagree)
PubChem entry: None findable
Primary reference: Coskun, Cell Metab 2022 (PMID 35985340)
Not to be confused with: Tirzepatide, LY3298176

What is actually verifiable

Less than for any other compound in this library. Searching PubChem for retatrutide, LY3437943 or LY-3437943 returns nothing, and CAS 2381089-83-2 does not resolve there either. That is unusual for a compound with Phase 3 data and a filing date, and it means the molecular weight and formula quoted everywhere trace to supplier catalogues and reference aggregators rather than to a primary chemical database.

Sources disagree on the formula

The commonly quoted figure is 4,731.33 Da for C221H342N46O68. At least one reference source gives C228H350N48O66 at approximately 4,894.58 Da instead. Both cannot be right. Where a compound has a settled database entry this kind of disagreement does not arise, and its presence here is a direct consequence of the absent entry.

Research material referenced

Retatrutide 10mg, third-party HPLC tested

Buy Retatrutide · £49.99

The identifier this category had wrong

Until this revision, these articles cited PubChem CID 156588324 as retatrutide. That record returns 4813 Da for C225H348N48O68, and its synonyms include Zepbound, tirzepatidum and 'Tirzepatide sodium salt (LY3298176)'. It is tirzepatide. The compound retatrutide is most often compared against, and the one it most needs to be distinguished from. The citation has been removed.

What can be relied on instead

Coskun and colleagues published the discovery and characterisation of LY3437943 in Cell Metabolism in September 2022, and that paper is the primary structural reference. Eli Lilly's investor releases carry the trial data. ClinicalTrials.gov carries the registrations. These are verifiable in a way the chemical identifiers currently are not.

What this means practically

Treat the 4,731 Da figure as reported rather than verified, and be aware that a certificate quoting a different formula is not necessarily wrong. Mass spectrometry against whichever value a certificate claims is the only check available, and where a supplier and a reference source disagree there is no authoritative record to arbitrate between them.

Frequently asked questions

What is retatrutide's CAS number?: 2381089-83-2 is the number commonly listed, though it does not resolve to a PubChem record.
Why is there no PubChem entry?: Not clear. Searches under the name, the development code and the CAS all return nothing, which is unusual for a compound at this stage of development.
Is CID 156588324 retatrutide?: No. That record is tirzepatide, its synonyms include Zepbound and LY3298176. It was cited in error here and has been removed.

Extended research context

The Retatrutide Research deep dive

Deep dive: how the triple-agonist scaffold was engineered

Retatrutide's 39-residue backbone was designed by Eli Lilly's peptide chemistry team to preserve the pharmacophores of three glucagon-family receptors on a single chain. The N-terminal domain retains GIP-receptor contacts, mid-chain substitutions restore GLP-1-receptor affinity lost in native GIP, and additional residue swaps confer glucagon-receptor engagement. A γGlu-2xOEG linker anchors a C20 fatty diacid at Lys17, which reversibly binds serum albumin and slows renal clearance. This is the same albumin-tethering strategy Novo Nordisk pioneered with semaglutide and Lilly refined further in tirzepatide.

The TRIUMPH Phase 3 programme in context

TRIUMPH is Lilly's global Phase 3 development umbrella for retatrutide, spanning obesity (TRIUMPH-1 through TRIUMPH-4), type 2 diabetes, MASH (metabolic dysfunction-associated steatohepatitis), and knee osteoarthritis linked to obesity. Readouts began in 2025 and continue through 2026. Because the compound is investigational, no regulator (FDA, EMA, or MHRA) has issued marketing authorisation, and legitimate supply exists only for laboratory reference and research contexts, never for human administration.

How retatrutide differs from tirzepatide and semaglutide at the mechanism level

Semaglutide is a mono-agonist (GLP-1 only). Tirzepatide is a dual agonist (GIP + GLP-1). Retatrutide adds glucagon-receptor activity, which pre-clinical and Phase 2 data suggest contributes to energy expenditure in addition to appetite regulation and glucose-dependent insulin release. This three-receptor combination is why retatrutide is sometimes called a 'metabolic multi-tool' peptide in the trade press, but the pharmacology is more nuanced than the label implies.

Research applications

▸In vitro receptor-binding assays across GIP-R, GLP-1R and GCGR panels
▸Comparator studies alongside semaglutide, tirzepatide and liraglutide reference standards
▸Analytical-method development: HPLC retention profiling and LC-MS confirmation
▸Stability testing of lipidated 39-residue peptides in aqueous and lyophilised forms
▸Reference material for teaching incretin pharmacology in university-level courses

Handling checklist

✓Store lyophilised vials at −20 °C; protect from light and humidity
✓Reconstitute with bacteriostatic water; avoid vortexing (foams the peptide)
✓Once reconstituted, store at 2–8 °C and use within 28 days
✓Verify batch CoA: HPLC ≥98%, mass matches ~4,731 Da, endotoxin low
✓Do not administer to humans or animals. Research use only

Common research-handling mistakes

Learnt from thousands of researcher orders across our UK labs.

✗ Confusing retatrutide with tirzepatide in supplier catalogues

Fix: Cross-check the LY code (LY3437943 = retatrutide; LY3298176 = tirzepatide) and the receptor profile on the CoA.

✗ Using tap or filtered water for reconstitution

Fix: Only use bacteriostatic water for injection (0.9% benzyl alcohol) or sterile water, never lab DI water.

✗ Storing reconstituted solution at room temperature

Fix: Refrigerate at 2–8 °C immediately after reconstitution; discard after 28 days.

Continue researching

Peer-reviewed guides, comparators and matched reference materials.

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.

UKP

Written and reviewed by

The UK Peptides Editorial Team · Research library, UK Peptides

The editorial team 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. Corrections are made in place and the review date updated.

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Retatrutide Chemical Identity: What Can Actually Be Verified