One receptor family, several molecules
In nearly every case the phrase means an incretin receptor agonist: semaglutide, tirzepatide, retatrutide and their relatives. They act on the GLP-1 receptor, sometimes alongside GIP and glucagon receptors, and they are administered by injection because peptides do not survive digestion.
The injection is not the mechanism. It is a delivery constraint. If these compounds could be taken orally in a stable form they would be, and considerable effort has gone into trying.
What separates the compounds from each other is how many receptors they engage, how long they stay in circulation, and how much clinical evidence sits behind them. Those three variables explain almost every difference you will read about.
The phrase weight loss injection is a lay description rather than a pharmacological one, which is why it attaches to licensed medicines, investigational compounds and market labels without distinguishing between them. Two of the molecules above exist as authorised medicines in the EU: semaglutide is the active substance of Wegovy, whose assessment report on the EMA website records what the regulator reviewed, and tirzepatide is the active substance of Mounjaro, assessed by the same agency. Retatrutide has no equivalent document because it remains investigational. What this catalogue supplies is none of those products: where it lists one of these molecules, it lists the compound itself, for laboratory work, with a certificate rather than a marketing authorisation behind it.
Four ways the compounds differ
The variables that actually distinguish one from another.
What we can and cannot say
We supply research material. We cannot tell you what any of these compounds will do for a person, we cannot recommend a protocol, and we will not write copy that implies otherwise however common that is in this market.
What we can do is describe the compounds accurately, say where the evidence comes from and how far it goes, and be specific about what is published versus what is repeated. That is what the pages linked below are for. One compound that turns up in the same searches without belonging to the incretin family at all is AOD-9604, a growth hormone fragment with a literature of its own and an approval history worth reading before anything else.
If you are looking for medical guidance on weight, a clinician is the right place to get it. If you are looking for accurately described research material with a certificate for the batch, that is what this catalogue is.
The compound files are where that accuracy lives. The tirzepatide page covers the dual agonist and the long argument about GIP that its trials ended, and the GLP-1 vs GLP-3 page deals with a label that appears on pens in this market without corresponding to any receptor. Both say plainly where the published evidence stops.
- One molecule, many namesThe same compound appears under research codes, brand names and market labels. The certificate names the compound.
- Phase 2 numbers quoted as settledEarly results are real but provisional. A completed programme is a different kind of claim.
- Effect sizes compared across trialsDifferent populations, durations and endpoints. Cross-trial comparison is not a like-for-like exercise.
- No mention of the classificationIf a page selling this material never says research use only, ask what else it has left out.
What we supply here
Every batch analysed by HPLC and released at 99% or above, with documentation per lot.
Read further
Three pages that go deeper than this overview.
About this category
What people ask when they arrive here from a search.