Peptide Info

What Is Retatrutide? The Triple Agonist Peptide Explained

Retatrutide, often shortened to reta, is a single peptide built to switch on three hormone receptors at once. This guide covers what it is, how triple agonism works, how it compares with tirzepatide and semaglutide, and where the trials are up to.

AussiePeptides Research Team 3 min read
Retatrutide 10mg research peptide vial with AussiePeptides label

Retatrutide at a glance

Retatrutide (development code LY3437943) is an investigational peptide from Eli Lilly. It is designed to activate three receptors with a single molecule: the GIP receptor, the GLP-1 receptor and the glucagon receptor. That is why it is called a triple agonist, why some media coverage nicknamed it "triple G", and why researchers and forums shorten it to reta. So if you have searched "whats reta" or "what is reta peptide", retatrutide is the compound you are looking for.

Developer
Eli Lilly
Code
LY3437943
Class
GIP / GLP-1 / glucagon tri-agonist
Half-life
About 6 days
Status
Investigational (phase 3)

It is not an approved medicine in Australia or anywhere else. Research suppliers sell it only as a laboratory reference peptide.

What is reta made of?

Retatrutide is a modified peptide chain with a fatty-acid side chain attached. That side chain lets the molecule bind to albumin, the most common protein in blood, which protects it from being broken down and cleared by the kidneys. The result is a long half-life: in early human studies it came out at roughly six days, which is why the clinical trials use once-weekly administration.

Research vials of retatrutide are supplied as a lyophilised (freeze-dried) powder. The powder is stable kept cold and dry, and is reconstituted with bacteriostatic water before laboratory use. Our reconstitution guide includes a worked retatrutide example.

How triple agonism works

Each of the three receptors is a separate signalling pathway that metabolic researchers already study on its own:

Receptor Natural hormone What researchers study it for
GLP-1 receptor Glucagon-like peptide-1 Insulin release, appetite signalling and gastric emptying
GIP receptor Glucose-dependent insulinotropic polypeptide Insulin release and fat tissue metabolism
Glucagon receptor Glucagon Energy expenditure and liver fat metabolism

Earlier drugs added these pathways one at a time. Retatrutide is the first widely studied compound to combine all three, and the question the trials are answering is whether the glucagon arm adds anything on top of the dual GIP and GLP-1 approach.

Retatrutide vs tirzepatide vs semaglutide

Peptide Receptors Typical half-life Status
Semaglutide GLP-1 About 7 days Approved medicine
Tirzepatide GIP + GLP-1 About 5 days Approved medicine (Mounjaro)
Retatrutide GIP + GLP-1 + glucagon About 6 days In clinical trials
Approximate elimination half-life (days)
  • Semaglutide~7 d
  • Retatrutide~6 d
  • Tirzepatide~5 d

Published approximate values from each compound's pharmacokinetic studies. All three are built for once-weekly dosing in trials.

For a deeper side-by-side, read retatrutide vs tirzepatide.

Where the research is up to

  1. June 2023Phase 2 obesity trial results published in the New England Journal of Medicine, bringing retatrutide to wide attention.
  2. 2023 onwardLilly runs the phase 3 TRIUMPH programme across several conditions.
  3. July 2026Lilly reports positive results from two more phase 3 obesity trials.
  4. August 2026Lilly says the clinical data package is complete.
  5. Q1 2027 (planned)Planned submission to the US FDA.
  6. 2029 (estimated)Primary completion of the TRIUMPH-Outcomes cardiovascular and kidney trial.

For what that means locally, see is retatrutide available in Australia?

Research-grade retatrutide and the COA

Because retatrutide is not approved anywhere, quality depends entirely on the supplier. Ask for a verified Certificate of Analysis that shows the HPLC purity result and a mass spectrometry identity check, and make sure the lot number matches your vial. Our COA and HPLC guide explains how to read one. AussiePeptides stocks retatrutide in 5mg to 60mg vials, each ≥99% pure with a verified COA.

Further reading

For laboratory research use only. Not for human consumption. Not medical or legal advice.

FAQ

Common questions

What is reta peptide?

Reta peptide is short for retatrutide, an investigational peptide from Eli Lilly that activates the GIP, GLP-1 and glucagon receptors.

Whats reta short for?

Reta is short for retatrutide. You may also see its development code, LY3437943, or the nickname triple G.

Is retatrutide the same as tirzepatide?

No. Tirzepatide targets two receptors (GIP and GLP-1). Retatrutide adds a third, the glucagon receptor.

What is the half-life of retatrutide?

Early human studies reported a half-life of roughly six days, which is why trials use once-weekly administration.

Is retatrutide approved?

No. As of October 2026 it is not approved by the US FDA or listed on the Australian Register of Therapeutic Goods.

Keep reading