Reference
Retatrutide vs tirzepatide vs semaglutide
The three compounds most often mentioned together, compared as molecules: what each is built to bind, how long it is, who made it and where it stands.
Most comparisons of these three are about results. This one is not: we make no claim about what any compound does, and nothing below compares effects. What it compares is the molecules themselves, which is where the real differences between them start.
At a glance
| Semaglutide | Tirzepatide | Retatrutide | |
|---|---|---|---|
| Receptors | 1: GLP-1 | 2: GIP, GLP-1 | 3: GIP, GLP-1, glucagon |
| Type | Single agonist | Dual agonist | Triple agonist |
| Length | 31 amino acids | 39 amino acids | 39 amino acids |
| Developer | Novo Nordisk | Eli Lilly | Eli Lilly |
| Development code | — | LY3298176 | LY3437943 |
| First US approval | December 2017 | May 2022 | Not approved |
| New Zealand | Approved medicine | Approved medicine (December 2025) | Not approved |
| People in trials before approval | 8,416 (SUSTAIN) | 7,215 (SURPASS) | 338 in phase 2; 3,100+ in two phase 3 trials reported in 2026 |
One, two, three receptors
The simplest way to tell them apart is by how many hormone receptors each molecule was designed to activate.
Semaglutide is a modified copy of GLP-1, a gut hormone the body makes itself. It targets one receptor. Natural GLP-1 lasts about two minutes in the blood; semaglutide has two amino acids swapped and a fatty-acid chain attached, which lets it bind to albumin in the blood and last about a week.
Tirzepatide is a single chain built to activate two receptors: GLP-1 and GIP, a second gut hormone. It carries a fatty-acid chain for the same reason semaglutide does.
Retatrutide adds a third: the glucagon receptor. That is why researchers nicknamed it “triple G”. Adding a third target is not simply more of the same; one sequence has to satisfy three binding sites at once, and the balance between them is what distinguishes one triple agonist from another.
The family tree
None of these started from scratch. The drug class began in 1992, when a researcher found a peptide in Gila monster venom, exendin-4, that acted like GLP-1 but resisted the enzyme that breaks GLP-1 down within minutes. It became exenatide, the first drug of its kind, and it is 39 amino acids long, the same length as tirzepatide and retatrutide. (History of GLP-1 drugs.)
All three also use building blocks that do not occur in nature, swapped into the chain so that the body’s enzymes cannot cut it the way they cut natural gut hormones. That, and the fatty-acid chains, are what separate a drug molecule from the hormone it imitates.
Why the two Lilly compounds are both 39
Tirzepatide and retatrutide sit one amino acid under the 40-amino-acid line the US regulator uses to separate a peptide from a protein. There is a rumour that this has to do with patents. It does not; the line decides which set of rules a molecule is approved under. The 40-amino-acid line, explained.
Where each one stands
- Semaglutide was approved in the United States in 2017 and is approved in New Zealand. It turned its developer into a company worth more, in 2023, than the whole annual economy of Denmark.
- Tirzepatide was approved in the United States in 2022 and by Medsafe in December 2025. It helped make Eli Lilly the first healthcare company valued at US$1 trillion.
- Retatrutide is not approved anywhere. Lilly began reporting its phase 3 (TRIUMPH) results in May 2026 and has said it plans to file for US approval in 2027. (Lilly, 2026.)
Material sold for laboratory research, including ours, is not any of the approved products and is not interchangeable with them. For more on each molecule: what is semaglutide, what is tirzepatide, what is retatrutide.
Buy in New Zealand
Prices, sizes and stock: Retatrutide in New Zealand · Tirzepatide in New Zealand · Semaglutide in New Zealand.
