How Retatrutide Works
Last updated 13 June 2026
Quick answer
The three signals, in plain words
1. GLP-1 (the "I'm full" signal)
GLP-1 is a gut hormone. It tells the brain you have eaten enough. It also helps the body handle sugar after a meal. Most popular weight peptides, like semaglutide, use this one signal.
2. GIP (the sugar helper)
GIP is another gut signal. It helps insulin do its job, so blood sugar stays steadier. Tirzepatide uses GLP-1 and GIP together.
3. Glucagon (the energy burner)
Glucagon helps the body use stored energy. This is the extra signal that most other peptides do not touch. It is the part that makes retatrutide a "triple" agonist.
Why three is a big deal
Older research peptides hit one or two of these signals. Retatrutide hits all three with one molecule. In trials, that mix lined up with larger changes in body weight. See retatrutide vs tirzepatide for a side-by-side.
What "GLP-3" really means
You may see retatrutide called a "GLP-3". That is just a nickname the media made up because it hits three targets. It is not a real science term. The proper name is triple receptor agonist.
How it is given in trials
In Eli Lilly's trials, retatrutide is a once-a-week injection under the skin. Its long half-life is what makes weekly dosing possible.
Looking at suppliers?
See where UK researchers source retatrutideCommon questions
What is a triple receptor agonist?+
Agonist means 'switch on'. Retatrutide switches on three receptors: GLP-1, GIP, and glucagon. That is why people call it a triple receptor agonist or triple agonist.
Why does the third signal matter?+
The glucagon signal can help the body burn more energy. Adding it to the other two is the main reason researchers think retatrutide may be stronger than older peptides in studies.
Is retatrutide a GLP-3?+
No. GLP-3 is an informal media nickname for triple agonists. It is not a real drug class. The correct term is triple receptor agonist.