Retatrutide vs Semaglutide: Identity and Chemistry Compared

Retatrutide and semaglutide are both synthetic peptides, and their classifications are where they split. Retatrutide is a GLP-1/GIP/glucagon triple receptor agonist. Semaglutide is a GLP-1 receptor agonist. Everything below is the detail behind that one-line difference.

Read this as a comparison of two molecules, not two outcomes. It covers CAS numbers, formulas, size, codes, and how each is supplied and tested. Kits Peptides does not claim either compound produces any result in anything, and nothing here ranks one over the other. An identity comparison has no winner.

The identity table

These are the values that pin down which molecule is in the vial. If you are logging a lot or reconciling two suppliers, the CAS number settles arguments.

One note on the weight row. The 4731.32 g/mol figure is the value on our own retatrutide label. I am not retyping one for semaglutide from memory when the number that matters is on your lot's certificate. Both formulas are free base. Peptides this size are commonly supplied as trifluoroacetate salts, and a TFA salt carries counterion mass a free-base formula does not describe.

What "triple agonist" is actually saying

Triple versus single is taxonomy. It is not a scoreboard.

Naming the receptors a molecule is characterized against places it in a class. Retatrutide sits with compounds characterized at three receptors: GLP-1, GIP, and glucagon. Semaglutide sits with compounds characterized at one. That count tells you how the literature files a molecule and nothing about what happens in any organism.

Size, and why the receptor count does not predict it

Retatrutide is the bigger molecule: 34 more carbons, 51 more hydrogens, one more nitrogen, nine more oxygens, 677 atoms against 582. Neither carries sulfur, so neither includes a cysteine or methionine residue. An S on either certificate means something is wrong with the document or the vial.

Now the counterexample. Tirzepatide, CAS 2023788-19-2, is a GLP-1/GIP dual receptor agonist with the formula C225H348N48O68: slightly larger than retatrutide on every element except oxygen, in a class with one fewer receptor named. Size does not track receptor count here, and reading "triple" as shorthand for "bigger" has the chemistry backwards.

Codes and registry numbers

Retatrutide still travels under its development code, LY-3437943, which appears in the literature about as often as the INN does. Semaglutide carries no alias on our listing: it has been indexed long enough that the generic name won.

The registry numbers date the same difference. CAS numbers are assigned in rough order of first indexing, so semaglutide's seven-digit 910463-68-2 sits well below retatrutide's ten-digit 2381089-83-2. Match the CAS number first, the formula second, and treat a mismatch on either as a stop sign, one of several in our red flags when buying research peptides.

How each is supplied and tested

Handling is where the two stop differing. Both ship lyophilized, freeze-dried to a dry cake, kept cold, sealed and out of light. Moisture and repeated temperature swings are what to limit. That is reagent storage, covered in storing lyophilized peptides, and none of it is preparation guidance.

Testing runs the same on both. Lots are sent to an independent third-party lab and the certificate publishes on that batch's page as the analysis completes. Our tested retatrutide lots were run by Krause Analytical in Austin, Texas. Semaglutide lots are awaiting analysis, so no certificate is published for them yet — the batch page will say so rather than imply otherwise. Mass spectrometry confirms the material is the molecule on the label, which for two peptides this close in size and class is the check that matters most. HPLC measures how much of the sample is target peptide against related impurities. I am not quoting purity figures, because the only honest one is on your own lot's certificate. What an HPLC purity percent means covers reading it.

The line this page does not cross

Both compounds appear in metabolic research literature. That is a subject heading, the drawer the papers are filed in, and naming it states what researchers have looked at, not what they reported.

I am deliberately not summarizing findings, and not saying which molecule anyone should prefer. This category draws a hard line between what a compound is and what anyone claims it does, and a comparison page is where that line gets crossed most often. The numbers above are your search terms for the primary sources.

Each product page shows its current batch and links the certificate where one has been published: retatrutide and semaglutide. If you have not read one of these certificates, start with how to read a peptide COA. Kits Peptides ships tracked from Vancouver, BC across Canada.

*All products are supplied as laboratory reagents for research use only. Not for human or veterinary use.*