Incretin receptor research has moved from single-target compounds to multi-receptor designs, and laboratories comparing them need clean specifications rather than marketing language. This guide compares three reference peptides used in laboratory research: semaglutide, tirzepatide and Retatrutide, the triple-receptor compound often called the GLP-3 peptide.
Semaglutide is a GLP-1 receptor mono-agonist and the single-receptor reference point in most comparative work. Tirzepatide activates both the GIP and GLP-1 receptors. Retatrutide adds glucagon receptor activity to GIP and GLP-1, so researchers can examine three signaling pathways in one molecule. Summit Labs lists retatrutide and tirzepatide (listed as GLP-2 (TR)) for laboratory use. We do not currently list semaglutide, so it appears here as a comparison reference only. Everything below is written for in vitro and laboratory research. It is not dosing, administration or medical guidance.
Molecular and Structural Comparison: Retatrutide Research Specifications
The table below summarizes the identifiers and receptor activity that researchers use to tell these three peptides apart. For the full retatrutide research specifications, including formula and storage details, see the retatrutide reference page and the tirzepatide reference page.
| Property | Semaglutide | Tirzepatide | Retatrutide (GLP-3) |
|---|---|---|---|
| Receptor activity | GLP-1 | GIP and GLP-1 | GIP, GLP-1 and glucagon |
| CAS number | 910463-68-2 | 2023788-19-2 | 2381089-83-2 |
| Molecular weight | about 4113.6 g/mol | 4813.5 g/mol | 4731.3 g/mol |
| Summit Labs lyophilized storage | Not listed | -20°C, sealed, protected from light | -20°C, sealed, protected from light |
| Summit Labs storage after reconstitution | Not listed | 2 to 8°C, use within 30 days | 2 to 8°C, use within 30 days |
Molecular weight is the number that matters most at the bench, because it is what a mass spectrometry result is compared against when confirming identity.
Laboratory Handling and Reconstitution
Lyophilized peptides arrive as a freeze-dried powder. Keep the vial sealed at -20°C and away from light until it is needed, and let it reach room temperature before opening so condensation does not form on the powder.
Reconstitution is done with a sterile diluent. Bacteriostatic Water contains 0.9% benzyl alcohol, which inhibits bacterial growth and allows a vial to be punctured more than once. Use sterile technique, add the diluent slowly down the wall of the vial, and swirl gently instead of shaking. Label the vial with the date, store it at 2 to 8°C, and avoid repeated freeze-thaw cycles. The Summit Labs listings for retatrutide and tirzepatide state that a reconstituted vial should be used within 30 days.
This article does not give volumes or concentrations for any compound. For a worked laboratory example of the arithmetic, read Reconstituting a Research Peptide Vial.
Purity Authentication and Quality Control
Two analytical methods sit behind most peptide quality reports. Reversed-phase HPLC separates the sample and reports purity as the share of the total peak area that belongs to the target peptide. Mass spectrometry measures the molecular weight of what is in the vial, which confirms identity against the expected value in the table above. Neither method says anything about how a compound behaves in a biological system.
A Certificate of Analysis is only useful if it belongs to the vial in your hands. Check that the lot number printed on the vial label matches the lot number on the certificate, then check the laboratory name, the report date and the reported purity. The COA Lookup page lets researchers search a lot number directly. Where a COA is published for the current lot, it is linked on the product page.
For a field-by-field walkthrough, see How to Read a Peptide Certificate of Analysis and HPLC and Mass Spectrometry: How Research Peptides Are Tested.
Conclusion and Research Resource Access
Semaglutide, tirzepatide and retatrutide represent one, two and three receptor targets, and the identifiers above are the fastest way to keep them apart in a laboratory notebook. If you plan to buy retatrutide for laboratory work, start with the product page and the lot COA. If you are comparing suppliers or searching for tirzepatide for sale, apply the same checks: matching lot numbers, a named testing laboratory and a report date you can verify.
More reference pages, testing guides and handling notes are collected in the Research Library.
All Summit Labs compounds are supplied for laboratory research use only. Not for human or veterinary use.
For laboratory research use only. Not for human or veterinary use.