Retatrutide: One Molecule, Three Hormone Receptors
Last updated: October 2026
Three gut and pancreas hormones, glucagon, GIP and GLP-1, each talk to their own receptor. For most of a century they were studied one at a time. Retatrutide is a single 39-amino-acid peptide designed to switch on all three receptors at once. Here is where the idea came from, what the lab and structural studies show, where the clinical program stands, and how a retatrutide batch is tested.
Three Hormones, One Chain
Retatrutide is the latest step in a long story: learning to make one molecule do the work of several hormones.
Glucagon was found in 1923, as a contaminant in early insulin extracts that raised blood sugar instead of lowering it. GIP was sequenced in 1971, and GLP-1 was shown to stimulate insulin release in 1987. All three are short peptides, and all three act through G protein-coupled receptors on the surface of cells: GCGR for glucagon, GIPR for GIP, and GLP-1R for GLP-1.
The hormones also look alike. Their sequences share enough of a family resemblance that chemists began asking whether one engineered peptide could be tuned to reach more than one of the receptors. In 2009 a team reported a glucagon and GLP-1 co-agonist in rodents. In 2015 the same group went further with a single peptide active at all three.
Retatrutide, developed under the code LY3437943, was described in 2022. It is built on a GIP-like backbone with a few non-standard amino acids that resist breakdown, and a long fatty acid that lets it ride on albumin in the blood, which is why it lasts for days rather than minutes. Research-grade retatrutide is made by chemical synthesis and supplied as a freeze-dried powder.
- 39 amino acidsPlus a C20 fatty diacid side chain
- Triple receptor agonistGIPR, GLP-1R and GCGR
- First described in 2022Coskun et al., Cell Metabolism
- Also calledLY3437943, LY-3437943
- CAS 2381089-83-2C221H342N46O68, about 4731 g/mol
Why Researchers Pay Attention to Retatrutide
Three findings explain why retatrutide stands out among incretin research peptides. Each one comes from a published paper.
Three receptors, one molecule
In engineered cell lines, each expressing a single human receptor, retatrutide switched on GIPR, GLP-1R and GCGR. Earlier designs in the same family reached one or two of them.
Coskun et al., 2022
Unbalanced on purpose
Retatrutide is not equally strong at each receptor. Compared with the native hormones, it was more potent at GIPR and less potent at GLP-1R and GCGR. That tilt toward GIP is part of the design.
Coskun et al., 2022 · Li et al., 2024
One helix, three locks
Cryo-electron microscopy shows retatrutide as one continuous helix in all three receptors. Its two ends do most of the work of deciding how well it fits each one.
Li et al., 2024
Three Receptors, Three Signals
Each receptor answers to its own hormone, and each sits in different tissues. Retatrutide is studied for how it engages all three.
Schematic, not to scale. One retatrutide molecule binds one receptor at a time; each receptor here holds its own copy.
GIPR, GLP-1R and GCGR
All three are class B G protein-coupled receptors. When a hormone binds, the receptor signals inside the cell, most famously by raising cyclic AMP (cAMP).
The 39 Amino Acids of Retatrutide
This is the whole chain, start to finish. Hover over or tap any position to see what it is. Look for the three non-standard residues and the one lysine that carries the fatty acid.
Two Aib residues and an α-methyl-leucine guard the chain against the enzymes that quickly break down the natural hormones. The fatty acid on lysine 17 binds albumin, which keeps the peptide circulating far longer.
| Sequence | Y-Aib-QGTFTSDYSI-αMeL-LDK-K*-AQ-Aib-AFIEYLLEGGPSSGAPPPS-NH2 (* lipidated lysine 17) |
|---|---|
| Molecular formula | C221H342N46O68 |
| Molecular weight | About 4731.3 g/mol |
| Side chain | A C20 fatty diacid joined to lysine 17 through a γ-glutamate and spacer linker |
| C-terminus | Amide (-NH2) |
| CAS number | 2381089-83-2 |
| KEGG DRUG | D12430 |
| Other names | LY3437943, LY-3437943 |
A Century of Research Behind Retatrutide
From a puzzling contaminant in insulin to a peptide built for three receptors, here is how the story unfolded, one chapter at a time. Keep scrolling.
- 1923
The contaminant in insulin
Kimball & Murlin, Journal of Biological Chemistry · pancreatic extracts
Within a couple of years of insulin's discovery, researchers preparing pancreas extracts noticed something odd: some fractions raised blood sugar before they lowered it. Kimball and Murlin traced the effect to a separate substance and named it glucagon, the glucose agonist. For decades it was seen mostly as insulin's opposite number, the hormone that tells the liver to release sugar.
- 1971
GIP gets a sequence
Brown & Dryburgh, Canadian Journal of Biochemistry · purified intestinal peptide
At the University of British Columbia, John Brown's team had purified a peptide from the upper intestine that slowed stomach acid secretion, and called it gastric inhibitory polypeptide. In 1971 they published its full amino-acid sequence. Its more important job, prompting the pancreas to release insulin after a meal, came into focus soon after, and GIP was renamed glucose-dependent insulinotropic polypeptide. It is a Canadian chapter in the story.
- 1987
GLP-1 steps forward
Mojsov et al., Journal of Clinical Investigation · Drucker et al., PNAS · isolated pancreas and islet cells
The glucagon gene turned out to encode more than glucagon. One of its other products, a fragment called glucagon-like peptide 1, was shown in 1987 to stimulate insulin release from the perfused rat pancreas, and to raise cAMP and insulin gene activity in islet cells. GIP and GLP-1 became known together as the incretins, the gut hormones that amplify insulin release after eating.
- 2009
Two hormones in one peptide
Day et al., Nature Chemical Biology · rodent studies
Glucagon and GLP-1 have opposite reputations, but chemists at Indiana University saw an opportunity in combining them. They engineered a single peptide active at both receptors. In rodent studies the two receptor signals appeared to act through different pathways. The idea of a deliberately mixed signal was born.
- 2015
The first triple agonist
Finan et al., Nature Medicine · rodent studies
The same research network went one step further: a single peptide balanced across all three receptors, GLP-1R, GIPR and GCGR. In rodent studies it was compared side by side with dual agonists, and the authors presented it as a rational design: each receptor arm tuned on purpose, not found by chance. It established the triple-agonist concept that retatrutide would later carry into the clinic.
- 2022
LY3437943 is unveiled
Coskun et al., Cell Metabolism · cell assays, mice and a phase 1 study
Eli Lilly scientists described LY3437943, now named retatrutide. In cells expressing single human receptors it activated all three, with balanced GCGR and GLP-1R activity and more GIPR activity. Mouse studies then traced its activity receptor by receptor, and a first-in-human phase 1 study characterized its pharmacokinetics.
- 2022
A first look at its timing
Urva et al., The Lancet · phase 1b trial
The first multi-week study, run as an investigational-medicine trial, characterized retatrutide's pharmacokinetics. Its half-life came out at about six days, consistent with the fatty-acid design.
- 2023
Phase 2 trials reported
Jastreboff et al., NEJM · Rosenstock et al., The Lancet · phase 2 trials
Two phase 2 trials of retatrutide as an investigational medicine were published in 2023. Both were randomized and placebo-controlled, and both were large enough to support moving the program into phase 3. Their full results are in the original papers, linked in the references below.
- 2024
Seeing it in the receptors
Li et al., Cell Discovery · cryo-electron microscopy
A Shanghai-led team solved structures of retatrutide bound to each of its three receptors, together with the G protein that carries the signal inside the cell. In every case the peptide formed one continuous helix: its N-terminal end reached deep into the receptor's core, while its C-terminal end rested on the receptor's outer domain. The two ends, rather than the middle, mainly decided how strongly it engaged each receptor.
- 2026
Phase 3 results begin to publish
Bajaj et al., The Lancet · Jastreboff et al., NEJM · Bellido et al., The Lancet · phase 3 trials
The large phase 3 programs, TRANSCEND and TRIUMPH, began reporting in peer-reviewed journals in 2026: TRANSCEND-T2D-1 in June, TRIUMPH-1 in September and TRIUMPH-2 in October. Retatrutide remains an investigational medicine. It is not approved in Canada or the United States.
So where does that leave us? Retatrutide is the clearest example so far of a peptide engineered to speak to three hormone receptors at once, with a deliberate tilt toward GIP. Its foundations are laid out in cell assays, rodent studies and receptor structures, and its clinical program is now in phase 3. None of that makes it an approved treatment, and each paper speaks for its own model, population and conditions, so the references below link every original.
Where Retatrutide Research Is Heading
The most interesting questions about retatrutide are about how its three signals add up. These are the ones researchers keep coming back to.
What does the glucagon arm add?
Mouse studies linked part of retatrutide's activity specifically to the glucagon receptor. How that signal behaves alongside the incretin signals in different tissues is the question that sets triple agonists apart from dual ones.
Coskun et al., 2022
Why tilt toward GIP?
Retatrutide is more potent at GIPR than native GIP, and less potent at the other two. Why that particular balance was chosen, and how changing it shifts signalling, is still being worked out.
Coskun et al., 2022 · Li et al., 2024
One peptide, three binding modes
Structures show the same helix seated slightly differently in each receptor, with GIPR's flexible first extracellular loop standing out. Those details are a map for designing the next generation of multi-receptor peptides.
Li et al., 2024
Built to last
Aib residues, an α-methyl-leucine and an albumin-binding fatty acid turn a hormone that lasts minutes into a peptide that lasts days. How each modification shapes receptor engagement is a research question in its own right.
Urva et al., 2022 · Li et al., 2024
In the clinic, separately. Retatrutide is being studied as an investigational medicine in phase 3 programs, with results published in 2026. It is not an approved drug: Health Canada's Drug Product Database lists no retatrutide product. The retatrutide supplied here is a research-grade peptide for laboratory study.
Retatrutide vs Tirzepatide at a Glance
Both are 39-amino-acid, fatty-acid-modified peptides from the same lab. The difference is one receptor.
| Retatrutide | Tirzepatide | |
|---|---|---|
| Receptors | GIPR, GLP-1R and GCGR (triple) | GIPR and GLP-1R (dual) |
| Length | 39 amino acids | 39 amino acids |
| Non-standard residues | Aib at 2 and 20, α-methyl-leucine at 13 | Aib at 2 and 13 |
| Fatty acid on | Lysine 17 | Lysine 20 |
| Reported half-life | About 6 days | About 5 days |
| Status | Investigational, phase 3 | Approved medicine in Canada and the US |
Reading a Retatrutide COA
A research guide is only as good as the material on the bench. A certificate of analysis answers four questions about a retatrutide batch.
Identity
Mass spectrometry measures the molecule's mass. A retatrutide result should sit close to 4731 Da, the mass of the full peptide with its fatty-acid side chain.
Purity
HPLC separates the sample and reports what share of the peptide signal is retatrutide rather than shorter or modified synthesis by-products.
Content
A milligram result for the tested vial, read against the amount on the label.
Endotoxin
The LAL test measures bacterial endotoxin, a contaminant that can skew cell-based experiments.
What's actually in the vial?
Synthetic peptides usually come out of purification with small charged partners, called counter-ions, attached to their charged groups. A long peptide like retatrutide has many charged groups, so they add weight to the powder but no peptide, and the milligrams of powder and the milligrams of retatrutide itself can differ.
The identity test isn't affected: mass spectrometry reads the retatrutide molecule itself. Where it matters is the content line. A good COA says whether its milligram figure means the peptide itself (net peptide content) or the powder as weighed, so you know exactly what you're working with.
When reading a retatrutide COA, match the batch number on the vial to the report and check that the sample is named as retatrutide. Our retatrutide batches are tested by SideChain Analytics, our primary laboratory in Canada, for identity, purity and endotoxin, with supplementary Janoshik reports for identity, purity, endotoxin and sterility. Every report is on our COA page and the Retatrutide (Reta) product page for Canada, and each one can be verified directly with the issuing lab.
Common Retatrutide Research Questions
What is retatrutide?
Retatrutide (LY3437943) is a synthetic 39-amino-acid peptide with a fatty-acid side chain. It activates three hormone receptors, GIPR, GLP-1R and the glucagon receptor (GCGR), and has been studied in cell assays, animal models and clinical trials as an investigational medicine.
Why is retatrutide called a triple agonist?
An agonist is a molecule that switches a receptor on. Retatrutide switches on three different receptors, the ones for GIP, GLP-1 and glucagon, so it is a triple agonist. Tirzepatide, by comparison, is a dual agonist at the GIP and GLP-1 receptors.
Is retatrutide the same as LY3437943?
Yes. LY3437943 is the development code Eli Lilly used before the name retatrutide was assigned. CAS number 2381089-83-2 identifies the same compound.
How is retatrutide different from tirzepatide?
Both are 39-amino-acid peptides with a C20 fatty acid. Tirzepatide acts at the GIP and GLP-1 receptors; retatrutide adds the glucagon receptor. They also differ in their non-standard residues and in which lysine carries the fatty acid. Our comparison guide covers this in detail.
Why does retatrutide last so long?
The natural hormones are broken down within minutes. Retatrutide's Aib residues and α-methyl-leucine resist the enzyme that cuts them, and its fatty acid binds albumin, a carrier protein in blood. In the phase 1b study its half-life was about six days.
What is Aib?
Aib (α-aminoisobutyric acid) is a non-standard amino acid with two methyl groups on its central carbon. It stiffens the chain and blocks the enzyme DPP-4, which normally cleaves GIP and GLP-1 near their start.
Has retatrutide been studied in people?
Yes, as an investigational medicine in phase 1, 2 and 3 clinical trials, with the first phase 3 results published in 2026. Research-grade retatrutide supplied for laboratory study is a different thing from an investigational drug product used in a regulated trial.
Is retatrutide approved by Health Canada?
No. Health Canada's Drug Product Database lists no retatrutide product. It is a research compound studied in laboratory, preclinical and clinical-trial settings, and the material offered here is supplied for laboratory and analytical research.
How should unopened vials be stored?
Keep the vial sealed, dry, protected from light and within any conditions stated in its batch documentation. The handling and storage guide covers this in more detail.
Glossary of Terms
Glucagon
A 29-amino-acid hormone from pancreatic alpha cells that signals the liver to release glucose.
GIP
Glucose-dependent insulinotropic polypeptide, a 42-amino-acid hormone from the upper intestine.
GLP-1
Glucagon-like peptide 1, a hormone from the lower intestine made from the same gene as glucagon.
Incretin
A gut hormone, such as GIP or GLP-1, that amplifies insulin release after eating.
Agonist
A molecule that binds a receptor and switches it on.
G protein-coupled receptor
A large family of cell-surface receptors that pass signals inside the cell through G proteins.
cAMP
Cyclic adenosine monophosphate, a messenger molecule inside cells that rises when these receptors are activated.
Aib
α-Aminoisobutyric acid, a non-standard amino acid that protects peptides from enzymatic cleavage.
Fatty diacid
A long-chain fatty acid with an acid group at each end. Attached to a peptide, it binds albumin and slows clearance.
Half-life
The time it takes for the amount of a compound in the body to fall by half.
Cryo-electron microscopy
A method that images frozen molecules to reveal their 3D structure, used here to see the peptide inside its receptors.
HPLC and LAL
HPLC (high-performance liquid chromatography) separates a sample to measure purity. The LAL test detects bacterial endotoxin.
References
- Kimball CP, Murlin JR (1923). Aqueous extracts of pancreas. III. Journal of Biological Chemistry 58(1):337–346. doi:10.1016/S0021-9258(18)85474-6
- Brown JC, Dryburgh JR (1971). A gastric inhibitory polypeptide. II. The complete amino acid sequence. Canadian Journal of Biochemistry 49(8):867–872. PubMed 5120249
- Mojsov S, Weir GC, Habener JF (1987). Insulinotropin: glucagon-like peptide I (7-37) co-encoded in the glucagon gene is a potent stimulator of insulin release in the perfused rat pancreas. Journal of Clinical Investigation 79(2):616–619. PubMed 3543057
- Drucker DJ et al. (1987). Glucagon-like peptide I stimulates insulin gene expression and increases cyclic AMP levels in a rat islet cell line. PNAS 84(10):3434–3438. PubMed 3033647
- Day JW et al. (2009). A new glucagon and GLP-1 co-agonist eliminates obesity in rodents. Nature Chemical Biology 5(10):749–757. PubMed 19597507
- Finan B et al. (2015). A rationally designed monomeric peptide triagonist corrects obesity and diabetes in rodents. Nature Medicine 21(1):27–36. PubMed 25485909
- Coskun T et al. (2022). LY3437943, a novel triple glucagon, GIP, and GLP-1 receptor agonist for glycemic control and weight loss: from discovery to clinical proof of concept. Cell Metabolism 34(9):1234–1247. PubMed 35985340
- Urva S et al. (2022). LY3437943, a novel triple GIP, GLP-1, and glucagon receptor agonist in people with type 2 diabetes: a phase 1b, multicentre, double-blind, placebo-controlled, randomised, multiple-ascending dose trial. The Lancet 400(10366):1869–1881. PubMed 36354040
- Jastreboff AM et al. (2023). Triple-hormone-receptor agonist retatrutide for obesity: a phase 2 trial. New England Journal of Medicine 389(6):514–526. PubMed 37366315
- Rosenstock J et al. (2023). Retatrutide, a GIP, GLP-1 and glucagon receptor agonist, for people with type 2 diabetes: a randomised, double-blind, placebo and active-controlled, parallel-group, phase 2 trial conducted in the USA. The Lancet 402(10401):529–544. PubMed 37385280
- Li W et al. (2024). Structural insights into the triple agonism at GLP-1R, GIPR and GCGR manifested by retatrutide. Cell Discovery 10(1):77. PubMed 39019866
- Bajaj HS et al. (2026). Efficacy and safety of retatrutide, a GIP, GLP-1, and glucagon receptor agonist, in people with type 2 diabetes and inadequate glycaemic control with diet and exercise (TRANSCEND-T2D-1): a double-blind, randomised, phase 3 trial. The Lancet 407(10546):2402–2413. PubMed 42250575
- Jastreboff AM et al. (2026). Retatrutide, a triple hormone receptor agonist, for treatment of obesity (TRIUMPH-1). New England Journal of Medicine, published online September 2026. PubMed 42814954
- Bellido V et al. (2026). Retatrutide in adults with obesity and type 2 diabetes (TRIUMPH-2): a double-blind, parallel-group, randomised, placebo-controlled, phase 3 trial. The Lancet 408:1455–1472. PubMed 42810372
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