Guide

Retatrutide vs tirzepatide: differences, trials and cagrilintide

Updated November 7, 2026

Tirzepatide acts on two receptors (GIP and GLP-1) and is an approved medicine (Mounjaro and Zepbound). Retatrutide acts on three (GIP, GLP-1 and glucagon) and is still investigational: FDA has not approved it. In published trials, retatrutide reached −24.2% body weight at 48 weeks in phase 2 and tirzepatide −20.9% at 72 weeks in phase 3, in different populations and durations.

Educational information about research compounds. Not medical advice. CaribePeptides products are sold for laboratory research only, not for human or veterinary use.

The difference in brief

Receptors: tirzepatide, GIP + GLP-1 (dual agonist). Retatrutide, GIP + GLP-1 + glucagon (triple agonist).
FDA status: tirzepatide approved as Mounjaro (May 13, 2022) and Zepbound (November 8, 2023). Retatrutide unapproved, in phase 3 trials (TRIUMPH programme).
Developer: both Eli Lilly; codes LY3298176 (tirzepatide) and LY3437943 (retatrutide).
Molecular mass: tirzepatide about 4813 g/mol; retatrutide about 4731 g/mol.
At CaribePeptides: G²-Tirz is tirzepatide and G³-Reta is retatrutide, both for research only.

What tirzepatide is

Tirzepatide is a synthetic 39-amino-acid peptide based on the GIP sequence, with a 20-carbon fatty acid chain that binds it to albumin and lengthens its time in the body. It activates the GIP and GLP-1 receptors; in 2020 cell studies its authors described it as an "imbalanced" agonist, with more action at GIP than at GLP-1.

As medicines, Mounjaro is approved for type 2 diabetes and Zepbound for chronic weight management, both on prescription. Research tirzepatide is neither.

What retatrutide is

Retatrutide is also a 39-amino-acid peptide with a 20-carbon fatty acid, but designed to activate a third receptor: glucagon’s. That is why it is called a triple agonist, and why social media calls it "GLP-3" or "Reta". Cryo-electron microscopy structures published in 2024 show how it binds each of the three receptors.

It is still an investigational drug. Lilly registered phase 3 as TRIUMPH on ClinicalTrials.gov; as of October 2026 several of those studies were still active. No retatrutide product is approved for sale as a medicine.

What the published trials showed

These results are from the medicines in controlled clinical trials, not from research material:

Tirzepatide (SURMOUNT-1, NEJM 2022). Adults with obesity or overweight without diabetes. At 72 weeks, body weight fell by an average of 20.9% at the highest dose studied, against 3.1% with placebo. The most common adverse events were gastrointestinal.
Retatrutide (phase 2, NEJM 2023). 338 adults with obesity. At 48 weeks, body weight fell by an average of 24.2% in the highest-dose group, against 2.1% with placebo. Gastrointestinal events also predominated, and heart rate rose with dose, peaking at 24 weeks.

The figures cannot be compared directly: the studies differ in phase, size and length. A fair comparison will come from retatrutide’s full phase 3 results.

And cagrilintide

Cagrilintide is not a GLP-1 agonist: it is a long-acting analog of amylin, a hormone the pancreas releases with insulin and that is linked to satiety. Novo Nordisk studies it combined with semaglutide (a combination known as CagriSema).

In the phase 3 REDEFINE 1 trial (NEJM 2025), with 3,417 participants, the combination achieved a mean weight reduction of 20.4% at 68 weeks, against 3.0% with placebo. Like retatrutide, it is not FDA-approved.

How to tell them apart on a COA

Because the names get mixed up on the market, the test that matters is mass spectrometry: tirzepatide gives about 4813 Da and retatrutide about 4731 Da, so a proper COA separates them without ambiguity. A method published in 2026 even identifies both, along with seven other peptides of the same class, in a single run.

Also check purity by HPLC and whether the analysis looked for molecules missing the fatty acid chain. See how to read a COA.

Products in this guide

Price per vial, live stock and lot COA on each page.

Retatrutide (G³-R)from $35 per vial
Tirzepatide (G²-T)from $60 per vial

Frequently asked questions

Is retatrutide the same as Mounjaro?

No. Mounjaro is tirzepatide, which acts on two receptors and is approved. Retatrutide is a different molecule, acts on three receptors and is still investigational.

Which is better, retatrutide or tirzepatide?

No published trial compares them head to head. Retatrutide showed −24.2% at 48 weeks in phase 2 and tirzepatide −20.9% at 72 weeks in phase 3, but these are different studies. What is clear: tirzepatide is approved and retatrutide is not.

When will FDA approve retatrutide?

FDA has announced no date. As of October 2026, several phase 3 studies were still active on ClinicalTrials.gov.

What are G³-Reta and G²-Tirz?

Our store names for research retatrutide (G³-Reta) and tirzepatide (G²-Tirz). They are sold for laboratory use only, with a lot COA.

Which organs does tirzepatide affect?

Its receptors are in the pancreas, brain, gut and fat tissue, among others. The adverse events reported most in trials were gastrointestinal; the Mounjaro and Zepbound labels list the full risks.