Retatrutide vs Tirzepatide
Quick Answer
Retatrutide adds a glucagon receptor; that is the whole pharmacological difference. Tirzepatide is a dual agonist of GLP-1R and GIPR (CAS 2023788-19-2, C225H348N48O68, 4,813 Da). Retatrutide agonises those two plus GCGR (CAS 2381089-83-2, 4,731 Da), which contributes thermogenesis and hepatic lipolysis. The evidence gap is as wide as the pharmacological one: tirzepatide has completed phase 3 and holds approvals; retatrutide has published phase 2 data only.
Compound Reference Pages
Retatrutide vs Tirzepatide: At a Glance
| Attribute | Retatrutide | Tirzepatide |
|---|---|---|
| Receptor targets | GLP-1R + GIPR + GCGR (triple) | GLP-1R + GIPR (dual) |
| Lilly development code | LY3437943 | LY3298176 |
| CAS number | 2381089-83-2 | 2023788-19-2 |
| Molecular weight | 4,731 Da | 4,813 Da (PubChem CID 166567236) |
| Molecular formula | Not publicly disclosed by Eli Lilly | C225H348N48O68 |
| Amino acid count | 39 residues per Lilly publications; full sequence not released | 39 residues; primary sequence published |
| Lipidation | Fatty-acylated for albumin binding; attachment site not disclosed | C20 fatty diacid at Lys20 via a γGlu-2×AEEA linker |
| Reported plasma half-life | Approximately 6 days in published phase 1 pharmacokinetics | Approximately 5 days in published pharmacokinetics |
| FDA status | Investigational — not approved for any indication | Approved drug products exist for type 2 diabetes and obesity; research-grade material is not those products |
| Clinical trial stage | Phase 2 published; phase 3 (TRIUMPH) ongoing | Phase 3 complete (SURPASS and SURMOUNT programmes) |
| Added receptor vs the other | GCGR — thermogenesis and hepatic lipolysis | None — tirzepatide is the pharmacological subset |
| Head-to-head trial against the other | None published | None published |
| Purity (Peptide.Express) | ≥99% by reverse-phase HPLC, batch CoA | ≥99% by reverse-phase HPLC, batch CoA |
How Retatrutide and Tirzepatide Differ in Research
These two compounds share a backbone architecture — both are 39-amino-acid fatty-acylated incretin analogs from the same developer — and differ in one respect that matters: retatrutide engages the glucagon receptor and tirzepatide does not.
That third receptor changes the metabolic direction of the molecule rather than simply amplifying it. GLP-1R and GIPR activation both act to lower glucose. GCGR activation raises hepatic glucose output, which sounds contradictory until you account for what else it does: it increases energy expenditure through thermogenesis and promotes lipolysis. The net glycaemic effect stays favourable because the GLP-1R arm counterbalances the glucagon arm, while the thermogenic and lipolytic effects add on top.
The regulatory gap between them is as important as the pharmacological one, and it is where most online comparisons are careless. Tirzepatide has completed phase 3 across the SURPASS and SURMOUNT programmes and there are approved drug products built on that record. Retatrutide has published phase 2 data and is in phase 3. Phase 2 runs smaller cohorts over shorter durations with different selection criteria, and drug development history is full of phase 2 effect sizes that did not survive phase 3. The Jastreboff 2023 NEJM retatrutide figures are real; they are also not yet confirmed, and no head-to-head trial of the two compounds has been published.
Two honest gaps close this out. Eli Lilly has not publicly released retatrutide's primary structure — any source quoting a full amino-acid sequence for it is not working from a disclosed reference — so Peptide.Express reports the molecular weight from the canonical entity record and leaves the formula field empty rather than filling it with an approximation. And the research-grade material sold here is not the approved pharmaceutical product in either case: it carries no regulatory review of its identity, purity or manufacturing controls, which is exactly why the batch Certificate of Analysis is the only quality signal worth weighing.
Frequently Asked Questions
What is the difference between retatrutide and tirzepatide?
The glucagon receptor. Tirzepatide activates GLP-1R and GIPR. Retatrutide activates those two plus GCGR, which adds thermogenesis and hepatic lipolysis to the pharmacology. Structurally both are 39-amino-acid fatty-acylated peptides of similar molecular weight.
Is retatrutide FDA approved?
No. Retatrutide is investigational, currently in Phase 3 trials, and is not approved by the FDA for any indication.
Is tirzepatide FDA approved?
Yes. Approved drug products containing tirzepatide exist for type 2 diabetes and for obesity, under separate brand names. That approval covers the pharmaceutical product manufactured and reviewed under those applications. Research-market tirzepatide is not that product and carries none of that regulatory review.
Is retatrutide better than tirzepatide?
No published trial has compared them directly, so there is no evidence-based answer. Retatrutide's reported figures come from a phase 2 trial; tirzepatide's come from completed phase 3 programmes. Comparing numbers generated at different trial phases, in different cohorts, over different durations is the single most common error made on this topic.
What is the difference in half-life?
They are close and both support weekly dosing. Retatrutide's published phase 1 pharmacokinetics report approximately six days; tirzepatide's published pharmacokinetics report approximately five. Both figures come from the fatty-acid chain each molecule carries, which binds serum albumin and keeps the peptide out of renal clearance.
Can retatrutide and tirzepatide be studied together?
No published study has tested the combination, and there is no mechanistic rationale for it. Retatrutide already agonises both receptors tirzepatide targets, so adding tirzepatide duplicates GLP-1R and GIPR activity without introducing a new pathway — while making any observed effect impossible to attribute to either compound.
Which has more published research behind it?
Tirzepatide, by a wide margin. It has completed phase 3 programmes across diabetes and obesity indications plus a growing post-approval literature. Retatrutide's human dataset is one published phase 2 trial and its phase 1 pharmacokinetics, with phase 3 still recruiting or ongoing.
What does triple agonist mean?
That a single molecule activates three separate receptors — in retatrutide's case GLP-1R, GIPR and GCGR. Dual agonism, as in tirzepatide, means two. The count matters because each receptor contributes a different metabolic action, and the glucagon receptor pushes in the opposite direction to the other two.
Why would activating the glucagon receptor be useful when glucagon raises blood sugar?
Because GCGR activation also drives thermogenesis and lipolysis, and the simultaneous GLP-1R activation counterbalances the glycaemic effect. The combination is what makes the third receptor additive rather than counterproductive.
What is retatrutide's amino acid sequence?
Not publicly disclosed. Eli Lilly has not released the primary structure. Sources presenting a complete sequence are not citing a disclosed reference.
Are both available at the same purity?
Yes. Both are verified at ≥99% purity by reverse-phase HPLC with LC-MS/MS molecular identity confirmation, and ship with a batch-specific Certificate of Analysis. All material is for in-vitro laboratory research use only.
References
- Jastreboff AM, Kaplan LM, Frías JP, et al. "Triple-Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial." New England Journal of Medicine, 2023. Read the retatrutide Phase 2 trial in NEJM
- "Retatrutide — A Game Changer in Obesity Pharmacotherapy." Review of the triple GLP-1/GIP/glucagon receptor agonist pharmacology and the trial evidence available prior to Phase 3 readout. Read the retatrutide obesity pharmacotherapy review on PMC
- "Efficacy and safety of retatrutide, a novel GLP-1, GIP, and glucagon receptor agonist." Systematic review of the published retatrutide efficacy and adverse-event data. Read the retatrutide efficacy and safety review on PMC
- Coskun T, Urva S, Roell WC, et al. "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. 2022. Read the Coskun 2022 retatrutide discovery and receptor pharmacology paper in Cell Metabolism
- Jastreboff AM, Aronne LJ, Ahmad NN, et al. "Tirzepatide Once Weekly for the Treatment of Obesity." New England Journal of Medicine, 2022. (SURMOUNT-1) Read the SURMOUNT-1 tirzepatide obesity trial in NEJM
- Coskun T, Sloop KW, Loghin C, et al. "LY3298176, a Novel Dual GIP and GLP-1 Receptor Agonist for the Treatment of Type 2 Diabetes Mellitus: From Discovery to Clinical Proof of Concept." Molecular Metabolism. 2018. Read the Coskun 2018 tirzepatide discovery and receptor pharmacology paper in Molecular Metabolism
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How This Page Is Sourced
Compiled by the Peptide.Express Research Team. Reviewed by Ben Laythee, Lead Chemist. Molecular identity on this page — name, CAS number, molecular formula and molecular weight — is resolved from a single internal entity record and checked against primary registries (PubChem, CAS Common Chemistry) rather than retyped per page. A field with no verified value is left out instead of estimated. Literature is cited to a DOI, PMID or PMCID permalink so every reference resolves to the specific record it names.