"Reta" means retatrutide
When people online say "reta", they mean retatrutide. It is a triple GLP-1/GIP/glucagon receptor agonist: one molecule that activates three separate hormone receptor systems. It is being studied in clinical trials for weight loss, and it has not completed the FDA approval process.
Why it gets called "GLP-3"
"GLP-3" is a nickname, not a drug class. The known glucagon-like peptides are GLP-1 and GLP-2 (teduglutide is a GLP-2 analogue), and there is no GLP-3 hormone or receptor.
The name comes from counting receptors. Semaglutide activates one, the GLP-1 receptor. Tirzepatide activates two, GLP-1 and GIP. Retatrutide activates three, adding the glucagon receptor, which is how it picked up the "GLP-3" label online. The nickname describes the number of targets, not a new hormone.
How the three receptors are thought to work
The GLP-1 receptor is associated with appetite suppression and slowed gastric emptying. The GIP receptor is associated with insulin signaling and fat metabolism. The glucagon receptor is associated with increased energy expenditure and fat oxidation. Activating all three at once, rather than one or two, is the proposed explanation for the size of the weight-loss effect seen in trials.
What the trials show so far
A phase 2 trial by Jastreboff and colleagues, published in the New England Journal of Medicine in 2023, reported body weight reduction of up to 24.2% at 48 weeks. A substudy of the same trial in people with MASLD (metabolic dysfunction-associated steatotic liver disease) reported reductions in liver fat.
The most commonly reported side effect is nausea, along with diarrhea, vomiting, constipation and decreased appetite, generally described as mild to moderate.
On our peptide tier list retatrutide is tier A: strong human trials, but not approved. A trial result describes what happened to the people in that trial, under medical supervision; it is not a prediction for anyone else.
Is retatrutide FDA-approved?
No. Retatrutide is an investigational compound and remains in clinical trials. Vials sold online as "reta" are research chemicals, not the trial drug, and no regulator checks what is in them or how pure they are.
Where to go next
The retatrutide reference page covers its mechanism, research and side effects with sources. If you are working out reconstitution math for a vial you already have, the retatrutide calculator converts vial size and water volume to syringe units; it does not suggest an amount. Side-by-side comparisons: semaglutide vs retatrutide, tirzepatide vs retatrutide, cagrilintide vs retatrutide and retatrutide vs tesamorelin.
Sources
- Triple-Hormone-Receptor Agonist Retatrutide for Obesity - A Phase 2 Trial. Jastreboff AM et al. N Engl J Med, 2023. Human trial
- Triple hormone receptor agonist retatrutide for metabolic dysfunction-associated steatotic liver disease: a randomized phase 2a trial. Sanyal AJ et al. Nature Medicine, 2024. Human trial
- Retatrutide: a triple incretin receptor agonist for obesity management. Ray A et al. Expert Opinion on Investigational Drugs, 2023. Review
Frequently asked questions
What is reta?
"Reta" is online shorthand for retatrutide, an investigational triple GLP-1/GIP/glucagon receptor agonist studied in clinical trials for weight loss.
Is GLP-3 real?
No. There is no GLP-3 hormone or receptor; the known glucagon-like peptides are GLP-1 and GLP-2. "GLP-3" is a nickname for retatrutide because it acts on three receptors: GLP-1, GIP and glucagon.
Is retatrutide FDA-approved?
No. Retatrutide is an investigational drug that remains in clinical trials and is not approved by the FDA.
How is retatrutide different from semaglutide and tirzepatide?
By the number of receptors it targets. Semaglutide activates the GLP-1 receptor, tirzepatide activates GLP-1 and GIP, and retatrutide activates GLP-1, GIP and glucagon. Semaglutide and tirzepatide are FDA-approved; retatrutide is not.
What did the retatrutide trial show?
A phase 2 trial published in the New England Journal of Medicine in 2023 reported body weight reduction of up to 24.2% at 48 weeks. Nausea was the most commonly reported side effect.
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