Retatrutide
What is GLP-3? The retatrutide nickname explained
There is no hormone called GLP-3. The name is an online nickname for retatrutide, the triple agonist. Here is where it comes from and what the trials of retatrutide found.
What it is
"GLP-3" is not a hormone. It is a nickname used online, and on some research product labels, for retatrutide, an investigational weekly injection from Eli Lilly. The body makes two related hormones, GLP-1 and GLP-2, both cut from the same precursor protein in the gut. GLP-1 helps regulate appetite and insulin. GLP-2 acts on the lining of the intestine, and a GLP-2 analogue called teduglutide is an approved medicine for short bowel syndrome. There is no third one.
The nickname comes from counting receptors. A receptor is a docking point on a cell; a molecule that switches it on is an agonist.
- One receptor: semaglutide switches on the GLP-1 receptor.
- Two receptors: tirzepatide switches on the GLP-1 and GIP receptors.
- Three receptors: retatrutide switches on the GLP-1, GIP and glucagon receptors (Coskun 2022).
Three receptors, third generation, hence "GLP-3". Some research pens carry the short name GLP3-RT, where RT stands for retatrutide.
What the studies looked at
Retatrutide was first described in 2022 under the code LY3437943, in cell and animal studies that showed it acting on all three receptors (Coskun 2022). It then went through a phase 2 trial in 338 adults with obesity (Jastreboff 2023) and the TRIUMPH phase 3 programme in over 5,800 people (Jastreboff 2026).
What the studies say
- Phase 2: −24.2 % mean weight change at 48 weeks with 12 mg, against −2.1 % with placebo, an injection with no active ingredient (Jastreboff 2023).
- TRIUMPH-1: −25.0 % at 80 weeks with 12 mg, against −3.9 % (Jastreboff 2026).
- For scale: semaglutide 2.4 mg was followed by −14.9 % at 68 weeks in STEP 1 (Wilding 2021) and tirzepatide 15 mg by −20.9 % at 72 weeks in SURMOUNT-1 (Jastreboff 2022). These were separate trials, so the numbers describe each trial and cannot be compared directly. The full comparison is in Retatrutide vs tirzepatide vs semaglutide.
What the researchers flagged
- The most common side effects were digestive, mostly mild to moderate, and heart rate rose in phase 2 before declining (Jastreboff 2023). All figures are on Retatrutide side effects.
- Retatrutide is investigational. Lilly planned its first application, in the United States, for early 2027 (Lilly, July 2026).
- "GLP-3" on a label says nothing about what is inside. Only an independent lab report tied to the batch does.
The extended breakdown
| Name | What it is | Receptors | Status, November 2026 |
|---|---|---|---|
| GLP-1 | Natural gut hormone | GLP-1 | Natural |
| GLP-2 | Natural gut hormone | GLP-2 | Natural; analogue teduglutide approved for short bowel syndrome |
| Semaglutide | Medicine | GLP-1 | Approved |
| Tirzepatide | Medicine | GLP-1, GIP | Approved |
| Retatrutide ("GLP-3") | Investigational compound | GLP-1, GIP, glucagon | Not approved |
Why add glucagon? Glucagon is usually known for raising blood sugar. In this design its receptor is switched on together with GLP-1 and GIP, and the early studies linked it to higher energy use and to the large fall in liver fat seen in the retatrutide trials (Coskun 2022, Jastreboff 2023).
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Extended breakdown
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Questions people ask
Is GLP-3 a real hormone?
No. The body makes GLP-1 and GLP-2, two hormones cut from the same precursor protein. There is no GLP-3. The term is an informal nickname for retatrutide.
Why is retatrutide called GLP-3?
Because it acts on three hormone receptors (GLP-1, GIP and glucagon), and people describe it as the third step after one-receptor drugs such as semaglutide and two-receptor drugs such as tirzepatide.
What does GLP3-RT on a pen mean?
Some research pens use GLP3-RT or GLP-3 RT as a short product name for retatrutide. It is a label, not a separate molecule. The content should always be confirmed by an independent lab report for the batch.
Is GLP-3 approved?
Retatrutide, the compound behind the nickname, was not approved as a medicine in the EU, the UK or the US as of November 2026.
What this page is, and is not
This page explains what published studies found. That is all it is. It is not medical advice, and it is not instructions for using anything. Nothing here is meant to find, treat, cure or stop any illness. The compounds discussed on this site are not approved medicines in the EU or the UK. Research compounds are sold for laboratory use only, not for use in humans or animals. A study tells you what happened to the people in it. It does not tell you what would happen to you. Talk to a doctor. This page is published by AuraVia Research Ltd, which sells research compounds.
Sources
- Coskun T et al., Cell Metab 2022, PMID 35985340 doi.org/10.1016/j.cmet.2022.07.013
- Jastreboff AM et al., N Engl J Med 2023, PMID 37366315 doi.org/10.1056/NEJMoa2301972
- Jastreboff AM et al., N Engl J Med 2026, TRIUMPH-1, PMID 42814954 doi.org/10.1056/NEJMoa2604169
- Wilding JPH et al., N Engl J Med 2021, STEP 1, PMID 33567185 doi.org/10.1056/NEJMoa2032183
- Jastreboff AM et al., N Engl J Med 2022, SURMOUNT-1, PMID 35658024 doi.org/10.1056/NEJMoa2206038
- Eli Lilly press release, 23 July 2026 (TRIUMPH-2 and TRIUMPH-3) investor.lilly.com/news-releases/news-release-details/lillys-triple-agonist-retatrutide-successful-two-additional
Related guides
Retatrutide: what the studies say, 2026 trial results
What the published retatrutide trials found in the people studied: weight, blood sugar, liver fat, side effects, and where it stands with regulators.
RetatrutideRetatrutide vs tirzepatide vs semaglutide: trial results
Retatrutide, tirzepatide and semaglutide side by side: how each works, the weight results of their main trials, side effects, and why the numbers are not directly comparable.
RetatrutideRetatrutide pen: what's inside and what the label means
A plain guide to the pre-filled retatrutide pen: what 15 mg or 40 mg on the label means, how a pen differs from a vial, and what the lab test of a pen batch found.
RetatrutideRetatrutide side effects: what the trials reported
Every side effect reported in the published retatrutide trials, with the percentages: nausea, diarrhoea, heart rate, skin sensations, low blood pressure and dropouts.