Retatrutide vs tirzepatide vs semaglutide
10 min read
Retatrutide, tirzepatide and semaglutide are the three compounds most often weighed against each other in incretin research, and they are the three most requested items in the metabolic part of our catalog. They are not three strengths of the same molecule. One targets a single receptor, one targets two, one targets three, and the number of receptors named in the literature is the shortest honest summary of what separates them. Two of the three are also close enough in mass that only a mass spectrometer can tell them apart. This guide sets all three side by side using the figures printed on our own certificates of analysis, and covers what actually changes at the bench when you move between them. For in-vitro laboratory research only.
On this page
- The three side by side
- One receptor, two, or three
- Chain length, mass, and what a milligram means
- The fatty-acid chain, and why all three have one
- Vial sizes and the concentration you end up with
- What is identical across all three
- Telling them apart on the certificate
- Why the three appear together
- Retatrutide, tirzepatide and semaglutide questions
The three side by side
Every figure below is the same data our certificate of analysis carries for the lot in your hand, not a general reference value.
Scroll the table sideways to see all three columns.
IdentityOne receptor, two, or three
The cleanest way to separate these three is to count the receptors each one is described as engaging in the published literature.
- Semaglutide is a 31-amino-acid GLP-1 analog. It is built on the GLP-1 backbone and is referenced as a single-receptor, or mono, agonist.
- Tirzepatide is a 39-amino-acid dual agonist, described as engaging both the GIP and the GLP-1 receptor.
- Retatrutide is a 39-amino-acid triple agonist, described as engaging GIP, GLP-1 and the glucagon receptor.
That ordering is also the order in which the three entered the literature, which is why they are so often listed as a sequence rather than as alternatives. They are three distinct molecules with three distinct sequences, and nothing about handling one tells you how another will behave in solution.
Our specification sheets carry the identity synonyms in the table above because the same molecule is published under several names, and the name on a vial is not an identity check. The CAS number and the observed mass on the lot certificate are.
ConcentrationChain length, mass, and what a milligram means
Semaglutide is the outlier on size: 31 residues and 4113.58, against 39 residues and roughly 4700 to 4800 for the other two. That is a gap of about 618 against retatrutide.
Milligrams measure mass, not molecules, so that gap changes what a milligram contains. A milligram of semaglutide is about 15 percent more molecules than a milligram of retatrutide, and about 17 percent more than a milligram of tirzepatide, purely because each semaglutide molecule weighs less. Anyone carrying a working volume across from one compound to another without recalculating is not running the comparison they think they are.
Tirzepatide and retatrutide sit at the opposite extreme. Both are 39 residues, both carry a C20-diacid, and they differ by 82 daltons on a molecule of roughly 4800, which is under two percent. Subtract the two formulas and the whole difference is C4H6N2, which is 82.1 by exact mass and accounts for the 82.12 the certificates report. Nothing you can see, weigh on a balance, or read off a label will separate those two. Mass spectrometry will, easily, because 82 daltons is a wide margin for that instrument.
The arithmetic itself is not judgement, so do not do it in your head. Enter the vial strength and your diluent volume in the reconstitution calculator and it returns the concentration and the exact draw for each vial separately.
StructureThe fatty-acid chain, and why all three have one
All three carry a fatty diacid chain attached to a lysine side chain: a C18-diacid on semaglutide at Lys26, and a C20-diacid on both tirzepatide at Lys20 and retatrutide at Lys17. This is a well-documented protein-engineering technique. The chain promotes reversible binding to serum albumin, and in the published pharmacokinetic literature that binding is what accounts for the long circulating half-life these molecules are studied for.
The backbone substitutions listed in the table serve a separate purpose. Aib is 2-aminoisobutyric acid, a non-proteinogenic residue. Semaglutide carries it at position 8 and tirzepatide at positions 2 and 13, in each case at a site where dipeptidyl peptidase-4 would otherwise cleave the native sequence. Semaglutide's Arg34 substitution replaces a second lysine so that acylation is directed to Lys26 and nowhere else.
None of this changes anything about how the vial is handled. It is here because it is what the sequence line on each certificate is describing, and because it explains why three molecules aimed at the same research area look so different on paper.
At the benchVial sizes and the concentration you end up with
Vial strength does more to set your working concentration than the choice of compound does. Semaglutide is supplied here as a 5mg vial. Tirzepatide and retatrutide both have a dosage selector on their product pages running well past that, tirzepatide from 5mg and retatrutide from 10mg, up to 60mg on either.
Put the same 2 mL of diluent into a 10mg vial and a 5mg vial and you get 5 mg/mL in one and 2.5 mg/mL in the other. Stack the molecular weights on top and a 10mg retatrutide vial holds roughly 1.7 times the number of molecules a 5mg semaglutide vial holds, not twice as many. Work the volume out per vial rather than per order, and work it out again whenever you change vial size.
The step-by-step method is in how to reconstitute research peptides, and the temperature and shelf-life detail is in how to store research peptides.
HandlingWhat is identical across all three
Most of the handling is the same, and that is worth stating plainly because the differences are easy to over-think:
- All three arrive as lyophilized powder and all three are stored the same way before reconstitution, at -20°C, with a 36 month shelf life on the unopened vial.
- All three are reconstituted with the same technique. Diluent runs down the glass wall, the vial is never shaken, and the cake is left to dissolve on its own.
- Once in solution, all three follow the same rule: refrigerated at 2 to 8°C, upright, out of light, and used within roughly 28 days when bacteriostatic water was the diluent.
- All three are released at ≥99% by HPLC, with identity confirmed by LC-MS and a certificate matched to the batch number printed on the vial.
So the volume decision is the only part of the workflow that genuinely changes when you move between them.
VerificationTelling them apart on the certificate
Semaglutide is easy: at 4113.58 it sits more than 600 daltons away from either of the others, and no instrument will confuse it with them.
Tirzepatide against retatrutide is the case that matters, and it is the reason to read the certificate rather than the label. Same chain length, same acyl chain length, 82 daltons apart. The vials look identical, the powders look identical, and the two names differ by three letters. The observed mass on an LC-MS trace is the only routine measurement that separates them, and 4813.45 against 4731.33 is not a distinction a mass spectrometer can blur.
Check the CAS number too, because it is unique per molecule and takes a second: 910463-68-2 for semaglutide, 2023788-19-2 for tirzepatide, 2381089-83-2 for retatrutide. If a document reports a mass or a CAS that does not sit where the named compound should, the label and the contents disagree, and that is the whole point of reading the document before you open the vial.
Every lot we release is assayed by reverse-phase HPLC and mass spectrometry. Look any batch up on the verify a certificate page, and how to read a certificate of analysis explains what each result on it means.
Research contextWhy the three appear together
These three names turn up in the same sentence because the published preclinical and clinical literature places them in one research area, incretin and metabolic signalling, and because each was described as adding a receptor to the one before it. That progression is the whole reason the comparison is asked for.
That is also the limit of what can honestly be said here. These are research reagents supplied for in-vitro laboratory work. Nothing on this page is a claim about outcomes, a protocol, a dose, or a recommendation to use any of these compounds in any living subject.
QuestionsRetatrutide, tirzepatide and semaglutide questions
What is the actual difference between retatrutide, tirzepatide and semaglutide?
The number of receptors each is described as engaging, and the sequence that follows from it. Semaglutide is a 31-amino-acid GLP-1 analog. Tirzepatide is a 39-amino-acid GIP and GLP-1 dual agonist. Retatrutide is a 39-amino-acid GIP, GLP-1 and glucagon triple agonist. Three distinct molecules with three distinct CAS numbers and three distinct masses.
Can you tell tirzepatide and retatrutide apart without a mass spectrometer?
Not reliably. Both are 39 amino acids, both carry a C20-diacid chain, and they differ by 82 daltons out of roughly 4800, which is under two percent. The powders and the vials look the same. LC-MS separates them without difficulty, 4813.45 against 4731.33, which is why the identity result on the lot certificate is the check that matters.
Is a milligram of one the same as a milligram of another?
No. A milligram is a mass, and these molecules do not weigh the same. Because semaglutide is the lightest at 4113.58, a milligram of it is about 15 percent more molecules than a milligram of retatrutide and about 17 percent more than a milligram of tirzepatide. Tirzepatide and retatrutide are within two percent of each other.
Do they store or reconstitute differently?
No. All three are lyophilized powder, stored at -20°C with a 36 month shelf life on the unopened vial, reconstituted with the same technique, and kept refrigerated at 2 to 8°C afterwards. What changes is the diluent volume, because that follows the vial strength you ordered rather than the compound.
Why does the specification sheet list brand names?
Because the same molecule is published and indexed under several names, and a researcher searching the literature needs to know they are reading about the same compound. They are listed as identity synonyms only. Our items are supplied as research reagents for in-vitro laboratory use and are not any of those products.
Which vial sizes do you supply?
Semaglutide is supplied as a 5mg vial. Tirzepatide runs from 5mg and retatrutide from 10mg, both up to 60mg, selectable from the dosage selector on their product pages. Current availability and dispatch times are shown on each product page, and every vial carries a per-batch certificate of analysis.
All three are released lot by lot, each with its batch number on the vial and its HPLC and LC-MS certificate on file. Read the specification and current lot for retatrutide, tirzepatide or semaglutide, or look up any batch on the verify page before you order.