Two related multi-receptor peptides
Retatrutide and tirzepatide are synthetic, lipidated peptides from the same research family: single molecules designed to act at more than one receptor for gut-derived hormones. Tirzepatide is described in the literature as a dual agonist of the GIP and GLP-1 receptors. Retatrutide is described as a triple agonist that adds activity at the glucagon receptor. Coskun et al.: tirzepatide characterisation. Li et al.: retatrutide receptor structures.
In the Morris Peppy catalogue, retatrutide is listed as GLP-3 (RT) and tirzepatide as GLP-2 (TZ). These are catalogue codes, not molecule names: “GLP-2 (TZ)” does not refer to the natural hormone glucagon-like peptide-2. Both are listed in 15 mg and 30 mg lyophilized vials, and each strength has its own batch record.
Side-by-side reference data
| Property | Retatrutide | Tirzepatide |
|---|---|---|
| Catalogue code | GLP-3 (RT) | GLP-2 (TZ) |
| CAS number | 2381089-83-2 | 2023788-19-2 |
| Molecular formula | C₂₂₁H₃₄₂N₄₆O₆₈ | C₂₂₅H₃₄₈N₄₈O₆₈ |
| Molecular weight | 4,731.33 g/mol | 4,813.5 g/mol |
| Receptor targets in the literature | GIP, GLP-1 and glucagon receptors | GIP and GLP-1 receptors |
| Structure | Linear peptide of about 39 residues with non-coded amino acids and a fatty diacid side chain | Linear peptide of about 39 residues with non-coded amino acids and a fatty diacid side chain |
| Regulatory status | Investigational compound in clinical trials; not an approved medicine | Approved prescription medicine in several jurisdictions |
| Listed vial strengths | 15 mg and 30 mg | 15 mg and 30 mg |
| Unopened vial storage | 2–8°C short term; −20°C or below longer term | 2–8°C short term; −20°C or below longer term |
Mechanism as described in the literature
The GIP, GLP-1 and glucagon receptors are class B G protein-coupled receptors. In cell-based studies they are usually compared by measuring cAMP signalling after receptor activation. Published characterisation of tirzepatide reports agonism at both the GIP and GLP-1 receptors, with a different balance of activity at each. Structural and signalling work on retatrutide examines how one peptide engages all three receptors. Li et al.: retatrutide receptor structures.
Both molecules carry a fatty diacid attached through a linker. In published pharmacokinetic work, this type of modification promotes reversible binding to albumin and extends circulating half-life compared with unmodified incretin peptides. Non-coded residues such as α-aminoisobutyric acid (Aib) are used in this family to resist cleavage by the enzyme DPP-4.
Typical research questions
- Receptor pharmacology: potency and signalling at individual receptors in engineered cell lines, including comparisons of dual and triple agonism.
- Structural biology: cryo-electron microscopy studies of how each peptide binds and activates its receptors.
- Preclinical physiology: how multi-receptor agonists affect energy balance, glucose handling and liver lipid measures in animal models.
- Clinical development: tirzepatide has been studied in large trial programmes in type 2 diabetes, obesity and related conditions; retatrutide is being evaluated in ongoing phase 3 programmes. Those trials used clinical formulations under medical supervision.
Trial endpoints belong to the specific populations and formulations studied. They are not claims about any research vial. Our research peptide reference notes list selected papers together with their limitations.
Analytical considerations: telling two similar molecules apart
The two molecules differ in molecular weight by about 82 g/mol (4,813.5 versus 4,731.33). Both are large, lipidated and fairly hydrophobic, so they can behave similarly on a reversed-phase HPLC column. A high HPLC purity result shows that one main peak dominates; it does not by itself show which of the two compounds that peak is. The distinction is explained in Peptide Purity vs Identity.
Identity is confirmed by mass spectrometry. In LC-MS, peptides of this size appear as several multiply charged ions that are deconvoluted to an intact mass. An 82 Da gap is easily resolved by routine instruments, so a correct LC-MS result separates GLP-3 (RT) from GLP-2 (TZ) clearly. Related impurities worth reading for include truncated or deletion sequences, oxidation and deamidation products, and variants of the lipid side chain.
Quantity is a separate question again. Lipidated peptides can adsorb to plastic and glass, and dry powder includes counterions and residual moisture, so measured peptide content is reported on its own stated basis. Read the 15 mg and 30 mg results as separate records.
How Morris Peppy tests each batch
Each Morris Peppy batch is tested by an independent U.S. laboratory. Five vials are selected at random from a single production run and put through a ten-check panel: purity (HPLC), quantity, identity, solubility, endotoxin (LAL), multi-vial conformity, fentanyl screening, container integrity, heavy metals and sterility.
Results for current batches are pending. A testing-in-progress card is not a completed result. Completed certificates of analysis are published on Lab Results before a batch is released, and each vial can be matched to its lot on Verify Product. The full process is described in how we test research peptides.
Storage and handling of lyophilized vials
Both products are supplied as freeze-dried powder, and the same guidance applies to unopened vials of either compound:
- On arrival, refrigerate unopened lyophilized vials at 2–8°C for short-term storage.
- For longer-term storage, −20°C or below is preferred.
- Keep vials sealed, away from light and moisture.
- Avoid repeated freeze–thaw cycles.
- Let a cold vial reach room temperature while still sealed before opening, to reduce condensation.
These conditions apply to sealed, dry material. They are not a shelf-life claim, and this page does not cover prepared solutions.
Before relying on a vial
- Match the full lot number and cap colour on Verify Product.
- Confirm that the identity result names the compound you expect; the codes GLP-3 (RT) and GLP-2 (TZ) are easy to confuse.
- Check the measured quantity for the exact strength, 15 mg or 30 mg.
- Read endotoxin, microbial, sterility and heavy-metal results separately from purity.
- Confirm the report through the issuing laboratory’s own verification route.
Frequently asked questions
What is the main structural difference between retatrutide and tirzepatide?
Both are lipidated peptides of about 39 amino acids. Retatrutide (C₂₂₁H₃₄₂N₄₆O₆₈, 4,731.33 g/mol) is described in the literature as a GIP, GLP-1 and glucagon receptor triple agonist, while tirzepatide (C₂₂₅H₃₄₈N₄₈O₆₈, 4,813.5 g/mol) is described as a GIP and GLP-1 receptor dual agonist.
Can HPLC alone tell retatrutide and tirzepatide apart?
Not reliably. HPLC purity shows how much of the measured signal belongs to the main peak. Identity needs mass spectrometry, which separates the two by their difference of about 82 g/mol in molecular weight.
Are retatrutide and tirzepatide approved medicines?
Tirzepatide is an approved prescription medicine in several jurisdictions. Retatrutide is an investigational compound in clinical trials and is not an approved medicine. Morris Peppy supplies both strictly for laboratory research, not for human or veterinary use.
What do the codes GLP-3 (RT) and GLP-2 (TZ) mean?
They are Morris Peppy catalogue codes. GLP-3 (RT) is retatrutide and GLP-2 (TZ) is tirzepatide. GLP-2 (TZ) does not refer to the natural hormone glucagon-like peptide-2.
How should unopened vials be stored?
Refrigerate unopened lyophilized vials at 2–8°C for short-term storage. For longer-term storage, −20°C or below is preferred. Keep vials sealed, away from light and moisture, and avoid repeated freeze–thaw cycles.
Are batch test results available?
Each batch goes through up to 10 checks at independent U.S. laboratories before release. Results for current batches are pending, and completed certificates of analysis are published on the Lab Results page before a batch is released.
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