Three generations of one idea
All three compounds descend from the same observation: activating the GLP-1 receptor changes glucose handling and appetite. Semaglutide does that and only that. Tirzepatide adds the GIP receptor. Retatrutide adds glucagon on top of both.
Each addition came with a striking trial result, and each successive trial programme is smaller and shorter than the one before it, because newer compounds have simply existed for less time. Effect sizes and evidence depth run in opposite directions across this table, and that tension is the whole comparison.
What follows is the factual position. It is not a recommendation, because ranking research compounds for use is precisely what a research-material supplier cannot and should not do.
A search for retatrutide vs tirzepatide vs semaglutide is usually a search for a ranking, and the published record supports something narrower. A third receptor widens what a molecule touches; it does not widen what has been observed about it. The two properties move independently, which is why the useful question is not which compound reaches furthest but which has been studied in the way your question needs. The pathway page covers the receptor biology all three share.
The three compounds, measured claims only
Everything in this table comes from published sources; nothing comes from forums.
| Semaglutide | Tirzepatide | Retatrutide | |
|---|---|---|---|
| Receptors | GLP-1 | GLP-1 + GIP | GLP-1 + GIP + glucagon |
| Evidence stage | Completed phase 3 programmes, plus outcome trials | Completed phase 3 programmes | Published phase 2 |
| Trial scale | Tens of thousands of participants | Thousands of participants | Hundreds of participants |
| Longest published exposure | Years | Around 18 months | Under one year |
| Reported weight effect | Large | Larger | Largest reported in class, at 48 weeks |
| Rare-event knowledge | Substantial | Growing | Minimal, trial too small to show it |
| In this catalogue | Research vial, 5 mg | Not stocked, reference page | Research vial, 30 mg |
Effect sizes come from different trials with different populations and endpoints. They indicate direction, not a like-for-like ranking.
Effect size against certainty
The pattern in the table is not an accident. Each newer molecule reports a bigger effect from a smaller body of evidence, because phase 2 exists to measure efficacy in a controlled group and phase 3 exists to find out what else is true. Retatrutide has not had its what-else phase yet.
That does not mean the phase 2 numbers are wrong. It means the error bars around everything else, rare effects, long-term effects, effects outside the trial population, are widest exactly where the headline number is largest.
Semaglutide sits at the other pole: the smallest headline effect of the three and by far the most complete picture around it. Tirzepatide sits between, in both senses. Where a given research question belongs on that axis is the researcher’s call, not ours.
None of this has to be taken on trust. Which studies exist, how many people they enrolled and whether they have reported is public in the registry entries on ClinicalTrials.gov, and for the molecules that have become authorised medicines the European assessment files go further, the EMA record for the semaglutide medicine Wegovy being the fullest of them. Half an hour with either source settles more than any supplier page can.
One line has to survive that reading. An authorised medicine and a research vial remain different products even when the molecule is spelled the same way: the approval, the assessment and the monitoring attach to the medicine, not to material sold for laboratory work, and the research-use-only page draws that boundary properly. It also explains why the sparse rare-event column above cannot be filled in from a medicine file, and why what is documented for retatrutide stops where its trials stop.
The two we stock
Both released at 99% or above by HPLC, with the batch certificate available before you order.
The compounds one by one
Each has its own page, with the evidence set out in full.
About this comparison
What people ask after reading the table.