Answer up front: the difference between these three research peptides is a count. Semaglutide reaches one docking point, tirzepatide reaches two, and retatrutide reaches three. Everything below is the published trial record for those molecules, set out as third-party research context. Lux BioPure supplies all three for laboratory research use only.
What is a receptor agonist, in plain words?
An agonist is a molecule that sits in a docking point on the outside of a cell and switches it on. The docking point is called a receptor, and the switch it throws is a signal the cell was already built to read.
Three docking points matter in this class, and each one carries a different set of signals:
- GLP-1. A gut hormone the body releases after eating. Its docking point is the one for moving food along the gut and for how insulin answers a rise in blood sugar. The same docking point carries the hunger signals the brain reads.
- GIP. A second gut hormone, also released after a meal. Its docking point is the one for the signals that handle fat and energy.
- Glucagon. The hormone that raises blood sugar, the opposite number to insulin. Its docking point is studied for how the liver uses fat for fuel, and for how much energy the body uses in a day.
A molecule that reaches one of the three is called a single agonist. One that reaches two is a dual agonist. One that reaches three is a triple agonist. That count, and nothing else about the chemistry, is what separates the three compounds compared here.
Which docking points does each molecule reach?
| Compound | GLP-1 | GIP | Glucagon | Trial named below |
|---|---|---|---|---|
| Semaglutide | Yes | No | No | STEP 5, 2022 |
| Tirzepatide | Yes | Yes | No | SURMOUNT-1, 2022 |
| Retatrutide | Yes | Yes | Yes | Phase 2, 2023 |
The pattern is additive on paper. Tirzepatide keeps the GLP-1 target semaglutide has and adds GIP. Retatrutide keeps both of those and adds glucagon. Nothing in this class reaches GIP or glucagon without reaching GLP-1 as well, which is why the glucagon column is the only one a single molecule has to itself.
What did the trials measure for each?
Semaglutide, a single agonist. In a two-year trial published in Nature Medicine in 2022, the STEP 5 trial, average weight in the group given the compound was 15.2% lower at week 104 than at the start. Both groups also followed the same behaviour programme, which is part of what was measured rather than a footnote to it. The semaglutide encyclopedia entry carries the rest of that record.
Tirzepatide, a dual agonist. In a 72-week trial of 2,539 adults published in the New England Journal of Medicine in 2022, average weight fell 22.5% at the highest dose studied, against 2.4% in the placebo group, the group given a dummy with no active drug in it. A separate 72-week trial of 938 adults who had both type 2 diabetes and obesity, published in The Lancet in 2023, reported average weight falling 15.7% at the highest dose studied. The tirzepatide entry sets those two studies side by side.
Retatrutide, a triple agonist. In a 48-week phase 2 trial of 338 adults published in the New England Journal of Medicine in 2023, average weight fell 24.2% in the highest-dose group, against 2.1% in the placebo group. In a 40-week phase 3 trial in adults with type 2 diabetes published in The Lancet in 2026, A1C, the blood test that shows the average blood sugar over about three months, fell by 1.7 to 2.0 percentage points across the doses studied, and weight fell by up to 16.8% at the highest dose studied. The retatrutide entry lists the same two papers.
Those are findings investigators reported in trial participants, people enrolled in registered studies and given the compound as a medicine under test. They are not a result for a vial, and not a result for any reader.
What is not known?
Three things, and together they are the reason the table above stops at a count.
The results are for whole molecules. No trial named here switched off one docking point and left the others running. A triple agonist was given, and a number came back. How much of that number belongs to GLP-1, how much to GIP and how much to glucagon was never separated, so single, dual and triple describe the design of a molecule and not a share of a result.
None of these trials ran the three compounds against each other. The populations differ, the lengths differ, and the doses differ. Reading the percentages down the page as a ranking would be comparing separate questions asked of separate groups of people over separate stretches of time.
Approval status is not uniform, and it is not a fact about a research vial. Semaglutide and tirzepatide carry FDA approval as finished drug products made by their developers. Retatrutide carries no approval anywhere: every retatrutide figure above comes from a compound still being tested. Nothing Lux BioPure sells is approved for human or veterinary use, and the approval record of a finished drug product says nothing about a freeze-dried research peptide in a vial.
How does this matter for a research design?
In one way only. It says what a protocol can hold constant and what it cannot.
A protocol that wants to vary the number of docking points has three molecules to vary it with, and the published record already says what has been measured at each count, in whom, and over how long. A protocol that wants the contribution of one docking point on its own has nothing on this page that will give it, because every molecule here reaches GLP-1 too, so the GLP-1 arm can never be the arm that is removed.
What the published record supports is a comparison of molecules. What it does not support is a comparison of switches. Any design that reads the three compounds as a dose ladder of the same thing has assumed the answer to the question the trials did not ask. A design that names each compound as its own arm, cites its own study, and reports its own timepoint stays inside what the literature actually measured.
The count of docking points, one, two and three, is the design difference between these three molecules, and every published number behind them is a whole-molecule number.
Sources
- Two-year effects of semaglutide in adults with overweight or obesity, the STEP 5 trial. Nature Medicine, 2022. pubmed.ncbi.nlm.nih.gov/36216945
- Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). New England Journal of Medicine, 2022. pubmed.ncbi.nlm.nih.gov/35658024
- Tirzepatide once weekly for the treatment of obesity in people with type 2 diabetes (SURMOUNT-2), a phase 3 trial. The Lancet, 2023. pubmed.ncbi.nlm.nih.gov/37385275
- Triple-Hormone-Receptor Agonist Retatrutide for Obesity, a Phase 2 Trial. New England Journal of Medicine, 2023. pubmed.ncbi.nlm.nih.gov/37366315
- Retatrutide in people with type 2 diabetes and inadequate control on diet and exercise (TRANSCEND-T2D-1), a phase 3 trial. The Lancet, 2026. pubmed.ncbi.nlm.nih.gov/42250575