How long is retatrutide?

39 residues, plus a C20 fatty diacid conjugated at Lys17 through a γGlu-2xOEG linker.

Why build it on GIP rather than GLP-1?

The three target receptors belong to one related family, and the GIP scaffold proved the workable starting point. It is the same choice Lilly made for tirzepatide.

What does the fatty acid do?

It binds serum albumin reversibly, which prevents renal filtration and shields the peptide from proteases, extending half-life.

Retatrutide Structure: 39 Residues on a GIP Scaffold

The short answer

Retatrutide is a 39-residue synthetic peptide built on a modified GIP scaffold, with a C20 fatty diacid conjugated through a γGlu-2xOEG linker at Lys17. The lipid binds serum albumin, extending half-life; the substitutions across the backbone create balanced activity at three receptors.

Key facts

Residues: 39
Backbone: Modified GIP scaffold
Lipidation site: Lys17
Linker: γGlu-2xOEG
Fatty acid: C20 diacid
Receptors: GIPR, GLP-1R, GCGR
Primary reference: Coskun, Cell Metab 2022

Why the backbone is GIP

This is the design decision that defines the molecule, and it is the same one Lilly made with tirzepatide. Rather than starting from GLP-1 and adding activity, both compounds start from GIP and engineer in the others. The three receptors (GIP, GLP-1 and glucagon) belong to one structurally related family, which is what makes a single scaffold capable of engaging all of them plausible at all.

What balanced agonism means

Balanced does not mean equal. It means the potencies at the three receptors sit within a range where all three contribute meaningfully at achievable concentrations, rather than one dominating so completely that the others are irrelevant. Achieving that across three related but distinct receptors, from one sequence, is the hard part of the design.

Research material referenced

Retatrutide 10mg, third-party HPLC tested

Buy Retatrutide · £49.99

The lipid and what it does

A C20 fatty diacid attached at Lys17 through a γGlu-2xOEG spacer. The diacid binds reversibly to serum albumin, which is too large to be filtered by the kidney and shields the peptide from proteases. This is the same strategy semaglutide uses with a C18 diacid and liraglutide with C16 palmitic acid, with chain length tuning the strength of binding and therefore the half-life.

Why the linker is not padding

The γGlu-2xOEG spacer sets the distance and flexibility between the albumin-binding lipid and the receptor-binding peptide. Get it wrong and albumin binding sterically blocks the peptide from reaching its receptors, or the lipid cannot reach albumin. It is a real design parameter rather than a connector.

Why Lys17 specifically

Lipidation needs a lysine side-chain amine to attach to, and it needs to be at a position where a bulky substituent does not interfere with receptor contact. Position 17 satisfies both. The same logic places semaglutide's chain at Lys26 and tirzepatide's at Lys20, each chosen for the same reasons within a different sequence.

Where the sequence is published

Coskun and colleagues described the discovery and characterisation of LY3437943 in Cell Metabolism in September 2022, and the sequence has appeared in Eli Lilly patent filings. That paper is the primary structural reference for anything in this article.

Frequently asked questions

How long is retatrutide?: 39 residues, plus a C20 fatty diacid conjugated at Lys17 through a γGlu-2xOEG linker.
Why build it on GIP rather than GLP-1?: The three target receptors belong to one related family, and the GIP scaffold proved the workable starting point. It is the same choice Lilly made for tirzepatide.
What does the fatty acid do?: It binds serum albumin reversibly, which prevents renal filtration and shields the peptide from proteases, extending half-life.

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.

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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 Structure and Sequence