Retatrutide vs Tirzepatide: What’s the Difference?
Retatrutide and tirzepatide are close relatives: both are 39-residue Eli Lilly peptides built on the GIP sequence, both carry a C20 fatty diacid that binds albumin, and both were developed for once-weekly dosing. The difference is one receptor.
Tirzepatide (LY3298176) is a dual agonist of the GIP and GLP-1 receptors. It is the active ingredient of FDA-approved Mounjaro and Zepbound. Research catalogues also list it as GLP-2 T or GLP-2 Tirz.
Retatrutide (LY3437943) activates the same two receptors plus the glucagon receptor. It is investigational, in phase 3, and not approved anywhere. Catalogues list it as GLP-3 R or GLP-3 Reta.
In short: retatrutide is tirzepatide's chemistry with glucagon-receptor activity added. A head-to-head phase 3 trial, TRIUMPH-5, was still running in October 2026.
Retatrutide vs Tirzepatide at a Glance
Both are 39-residue peptides on the GIP backbone with a C20 fatty diacid. Retatrutide (C221H342N46O68, 4,731.34 g/mol) activates three receptors; tirzepatide (C225H348N48O68, 4,813.53 g/mol per the FDA label) activates two. Tirzepatide is FDA-approved; retatrutide is not approved anywhere.
| Comparison | Retatrutide | Tirzepatide |
|---|---|---|
| Peptide length | 39 amino acids | 39 amino acids |
| Molecular weight | 4,731.34 g/mol | 4,813.53 g/mol |
| Sequence | YXQGTFTSDYSILLDKKAQXAFIEYLLEGGPSSGAPPPS-NH2 | YXEGTFTSDYSIXLDKIAQKAFVQWLIAGGPSSGAPPPS-NH2 |
| Molecular relationship | GIP-backbone triple agonist | GIP-backbone dual agonist |
| Receptor activity | GIP, GLP-1 and glucagon receptor signalling | GIP and GLP-1 receptor signalling |
| Research evidence | Phase 1–3 trials; investigational | Large phase 3 and outcomes trials; FDA-approved |
| FDA-approved drug | No | Yes (Mounjaro, Zepbound) |
What are Retatrutide and Tirzepatide
39 AA
Retatrutide
A 39-residue lipidated peptide from Eli Lilly that activates the GIP, GLP-1 and glucagon receptors in one molecule.
Research areas
GIPR • GLP-1R • GCGR • Metabolic models
X = Aib at positions 2 and 20; position 13 is α-methyl-leucine; Lys17 carries a C20 fatty diacid through a γGlu–AEEA linker. In vitro it showed balanced glucagon- and GLP-1-receptor activity with more GIP-receptor activity, and its half-life in a phase 1b study was about 6 days.
Explore GLP-3 Reta (retatrutide)39 AA
Tirzepatide
A 39-residue lipidated peptide from Eli Lilly that activates the GIP and GLP-1 receptors, with more engagement of the GIP receptor at clinical exposures.
Research areas
GIPR • GLP-1R • Incretin biology • Metabolic models
X = Aib at positions 2 and 13; Lys20 carries a C20 fatty diacid through γGlu and two AEEA linkers. Lilly's pharmacology work calls it imbalanced (more GIPR than GLP-1R engagement) and biased toward cAMP at GLP-1R. The FDA label gives a half-life of about 5 days.
Explore GLP-2 Tirz (tirzepatide)Tirzepatide: GIPR + GLP-1R+ glucagon receptorRetatrutide: GIPR + GLP-1R + GCGR
Same GIP backbone and C20 diacid; one more receptor
Key Differences Between Retatrutide and Tirzepatide
| Key differences | Retatrutide | Tirzepatide |
|---|---|---|
| Receptors | Three: GIP receptor, GLP-1 receptor and glucagon receptor. |
Two: GIP receptor and GLP-1 receptor. |
| Lipidation | C20 fatty diacid on Lys17 via γGlu–AEEA. |
C20 fatty diacid on Lys20 via γGlu and two AEEA units. |
| Unnatural residues | Aib at 2 and 20; α-methyl-leucine at 13. |
Aib at 2 and 13. |
| Reported half-life | About 6 days (phase 1b, type 2 diabetes). |
About 5 days (FDA label). |
| Clinical programme | Phase 2 (NEJM, Lancet 2023) and phase 3 TRIUMPH and TRANSCEND-T2D trials, first results published in 2026. |
Phase 3 SURPASS (type 2 diabetes) and SURMOUNT (obesity) programmes, plus SURMOUNT-OSA and the SURPASS-CVOT outcomes trial. |
| Status | Investigational; not approved anywhere. |
FDA-approved as Mounjaro (May 2022) and Zepbound (November 2023). |
How their research profiles differ
- Retatrutide
- 39-AA GIP-backbone peptide
- GIP + GLP-1 + glucagon receptors
- Triple-agonist metabolic research
- Tirzepatide
- 39-AA GIP-backbone peptide
- GIP + GLP-1 receptors
- Dual-agonist incretin research
Retatrutide vs Tirzepatide: Which Is Better?
There is no head-to-head result to answer that yet. Each was studied in its own trials, with different populations, durations and end points, and results from separate trials cannot be compared as if they came from one randomised comparison.
The direct comparison is TRIUMPH-5 (NCT06662383), a phase 3 trial of retatrutide against tirzepatide in obesity, which was still running in October 2026.
For research purposes the useful distinction is pharmacological: tirzepatide is a two-receptor model, and retatrutide adds glucagon-receptor activity on top of it. That changes the question being asked, not just the size of an effect.
Does the model need dual GIP/GLP-1 receptor agonism, or the added glucagon-receptor component that retatrutide brings?
Can Retatrutide and Tirzepatide Be Studied Together?
They can be compared in the same research programme, as separate groups, when the aim is to isolate what glucagon-receptor activity adds to a GIP/GLP-1 background. That is the design of TRIUMPH-5.
Giving both in the same condition is a different matter: they overlap at the GIP and GLP-1 receptors, so their effects could not be told apart.
There Isn’t One Universal “Winner”
Retatrutide
Triple-agonist research profile
GIP • GLP-1 • glucagon • investigational
Tirzepatide
Dual-agonist research profile
GIP • GLP-1 • FDA-approved molecule
Compare the Research. Verify the Material.
Clean Peptide stocks retatrutide as GLP-3 Reta and tirzepatide as GLP-2 Tirz. Every size ships against the certificate for its own lot, with the lot number, laboratory, HPLC purity and identity result listed on the product page.
The retatrutide lots are analysed by ILS Laboratories with a full QC panel. The tirzepatide lots come from HYTE Research Division (20 mg) and Accurate Test Labs (30 mg).
Question
Frequently Asked
What is the difference between retatrutide and tirzepatide?
Tirzepatide activates two receptors, GIP and GLP-1. Retatrutide activates those two plus the glucagon receptor. Both are 39-residue Eli Lilly peptides on the GIP backbone with a C20 fatty diacid.
Is retatrutide stronger than tirzepatide?
No head-to-head result has been published. The two were studied in separate trials, which cannot be compared directly. TRIUMPH-5 (NCT06662383), a phase 3 trial of retatrutide against tirzepatide, was still running in October 2026.
What is retatrutide vs Zepbound or Mounjaro?
Zepbound and Mounjaro are Eli Lilly's brand names for tirzepatide. So retatrutide vs Zepbound is the same comparison: a triple GIP/GLP-1/glucagon agonist against a dual GIP/GLP-1 agonist.
Is GLP-3 R vs GLP-2 T the same comparison?
Yes. GLP-3 R (also GLP-3 RT or GLP-3 Reta) is the catalogue label for retatrutide, and GLP-2 T (GLP-2 Tirz) is the label for tirzepatide, so GLP-3 R vs GLP-2 T is retatrutide vs tirzepatide.
Are retatrutide and tirzepatide made by the same company?
Yes. Both were developed by Eli Lilly. Retatrutide is LY3437943 and tirzepatide is LY3298176.
How long are their half-lives?
Tirzepatide's half-life is about 5 days per its FDA label; retatrutide's was about 6 days in a phase 1b study. Both were given once weekly in trials.
Is retatrutide FDA-approved?
No. Retatrutide is investigational and not approved by any regulator. Tirzepatide is FDA-approved as Mounjaro and Zepbound.
Why are they called GLP-3 and GLP-2?
Those are catalogue labels for the number of receptors (three and two), not scientific names. Retatrutide is not a "GLP-3" hormone and tirzepatide is not a GLP-2 agonist.
Research Peptides. Documented by Batch.
Every size in the catalogue ships against the certificate issued for its own lot.
For laboratory research use only. Not for human or veterinary use.
References
Identity data come from the FDA labels, the FDA substance registry (GSRS), KEGG and PubChem. Trial descriptions follow the PubMed abstracts.
- Coskun T, 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. Discovery and receptor profile of retatrutide.
- Urva S, et al. 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 Lancet, 2022. Half-life of about 6 days.
- Coskun T, 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. Discovery of tirzepatide.
- Willard FS, et al. Tirzepatide is an imbalanced and biased dual GIP and GLP-1 receptor agonist JCI Insight, 2020. Receptor pharmacology.
- Li W, et al. Structural insights into the triple agonism at GLP-1R, GIPR and GCGR manifested by retatrutide Cell Discovery, 2024. Acylation sites of semaglutide, tirzepatide and retatrutide.
- Jastreboff AM, et al. Retatrutide, a Triple Hormone Receptor Agonist, for Treatment of Obesity NEJM, 2026. Phase 3 TRIUMPH-1.
- FDA label Mounjaro (tirzepatide) injection Structure, formula, molecular weight and half-life.
- ClinicalTrials.gov NCT06662383 (TRIUMPH-5) Phase 3, retatrutide vs tirzepatide in obesity; ongoing.
