Retatrutide: A Research Primer

Retatrutide is a synthetic peptide roughly 39 amino acids long, classed as an agonist at three receptors instead of one: the GLP-1 receptor, the GIP receptor, and the glucagon receptor. In the development literature it is written as LY-3437943, and it carries CAS number 2381089-83-2. That is the identity. Everything below is the detail behind it.

This is an identity primer, not a usage page. It covers what the molecule is, what the label figures refer to, which literature cites it, and how it is handled and verified as a reagent.

What retatrutide is

Retatrutide is a single-chain synthetic peptide, assembled residue by residue rather than isolated from any tissue. The phrase doing most of the work in any description of it is "triple receptor agonist", and that is a classification, not a claim. It says the sequence was engineered to bind three receptors: the receptor for GLP-1 (glucagon-like peptide-1), the receptor for GIP (glucose-dependent insulinotropic polypeptide), and the glucagon receptor. Naming what a molecule was designed to bind is a structural fact about the molecule. It says nothing about what follows from that, and this page is not going to.

Structurally it sits in the same engineered lineage as tirzepatide, the dual GIP/GLP-1 agonist: a long chain rather than a short fragment, carrying non-standard residues and a fatty-acid side chain that plain peptides do not have. At 4,731.32 g/mol it is at the heavy end of what still gets called a peptide instead of a small protein.

The LY-3437943 code

LY-3437943 is the development code, the LY prefix being Eli Lilly's internal series marker. Codes like that are assigned long before a compound has a generic name, so the earliest papers and registry entries use the number.

"Retatrutide" is the later International Nonproprietary Name. The -tide ending is the standard suffix flagging a peptide, the same convention behind semaglutide and tirzepatide. Both names point at one compound, and the literature is split between them, so search both strings plus the CAS number.

The chemistry on the label

These are the values that pin down which molecule is in the vial. If you are logging a lot or comparing two suppliers, the CAS number is the one that settles arguments.

• CAS number: 2381089-83-2
• Molecular formula: C221H342N46O68
• Molecular weight: 4731.32 g/mol
• Class: GLP-1/GIP/glucagon triple receptor agonist
• Other names: LY-3437943
• Length: approximately 39 amino acids

That formula is the free base. Synthetic peptides are commonly supplied as trifluoroacetate salts, a residue of the purification step, and the salt adds counter-ion mass without changing which peptide you have. A certificate may report net peptide content separately for that reason. Do not read the free-base formula as a description of the salt.

A name can be transcribed a dozen ways and a formula can be mistyped. A registry number cannot be argued with. Match the CAS number first, then the formula, then the mass.

Where it appears in the research literature

Retatrutide appears in metabolic-science research. That names the field and stops there.

I am deliberately not summarizing findings. There is a hard line between describing what a compound is and describing what anyone reports it doing, and a primer stays on the identity side of it. If you want the actual work, search "retatrutide", "LY-3437943", or the CAS number and read the primary sources.

Chemists file it by target, next to GLP-1 receptor agonists like semaglutide and dual GIP/GLP-1 agonists like tirzepatide. One, two, or three receptors describes design, not ranking.

How it is supplied and handled

Retatrutide ships lyophilized, freeze-dried to a dry cake, because a solid survives transit far better than a solution. It is stocked in vial sizes from 5 mg to 60 mg; the number on the label is how much peptide is in the vial, nothing more.

Store it at -20C, keep the vial sealed in storage, and keep it out of light. Because the molecule is lipidated it is less forgiving of repeated temperature swings than a short unmodified peptide. Freeze-dried vials usually contain a bulking agent so there is a visible cake, and a proper certificate accounts for that filler in the stated mass. This is reagent handling, not preparation guidance.

How the lots are tested

Lots are sent to an independent laboratory and each tested batch gets its own certificate, published as the analysis completes. Purity is measured by HPLC read at 220 nm, the wavelength the peptide bond absorbs at, and identity is confirmed by mass spectrometry, which checks that the molecule matches the label rather than only measuring how clean the sample is. For a lipidated peptide of this mass the mass-spec step carries extra weight, since a fatty-acid side chain is exactly the structural feature a mislabeled or truncated sample gets wrong.

Our tested retatrutide lots were analysed by Krause Analytical in Austin, Texas, and the full COA PDF is published on that batch's page. Other compounds in the catalogue have gone to other independent labs; the certificate always names the lab that ran the lot. If you have not worked through one before, there is a walkthrough on how to read a peptide COA using real reports. Current batch and stock status are on the retatrutide product page. Kits Peptides ships tracked from Vancouver, BC across Canada.

*All products are supplied as laboratory reagents for research use only. Not for human or veterinary use.*