What is Retatrutide?
Retatrutide is a triple agonist that simultaneously activates three receptors: GIP, GLP-1, and glucagon (GCGR). It is considered the next frontier in metabolic pharmacology — dubbed a “triagonist” — and represents the natural evolution after twincretins like tirzepatide.
The “GLP-3” phenomenon
When you hear “GLP-3,” nobody is talking about a real biological receptor — it doesn’t exist. It’s the informal nickname that the press and biohacking communities use for this new generation of triple agonists. The logic is simple: if GLP-1 is the first generation and GLP-1+GIP (tirzepatide) is the second, this triple-action category was colloquially dubbed “GLP-3.”
What these drugs activate are three distinct hormonal receptors:
| Receptor | Full name | Primary effect |
|---|---|---|
| GLP-1 | Glucagon-like peptide-1 | Reduces appetite · slows gastric emptying |
| GIP | Glucose-dependent insulinotropic polypeptide | Optimizes insulin · fat metabolism |
| Glucagon | Glucagon receptor (GCGR) | Increases energy expenditure · hepatic thermogenesis |
The difference from prior drugs: monoagonists (semaglutide) activate only GLP-1. Dual agonists (tirzepatide) activate GLP-1 + GIP. Triple agonists like retatrutide activate all three — hence the nickname.
To access the clinical trials behind these data points, see the sources section at the bottom of this profile.
The third receptor: glucagon
Adding glucagon agonism is the key differentiator:
- The glucagon receptor (GCGR) increases hepatic energy expenditure and fatty acid oxidation.
- In combination with GIP and GLP-1, it produces a thermogenic effect that accelerates fat loss beyond simple caloric intake reduction.
- Glucagon also has direct effects on brown adipose tissue (thermogenesis).
The historical concern with glucagon agonism was glucose elevation (glucagon is hyperglycemic). Retatrutide resolves this by combining it with the insulinotropic effects of GIP and GLP-1, creating a net favorable metabolic balance.
Phase 2 results (NEJM, 2023)
The 48-week study with 338 non-diabetic participants showed:
- 12 mg/week: average weight loss of 24.2% — equivalent to nearly 1/4 of body weight.
- 8 mg/week: weight loss of 22.8%.
- No other drug in clinical trials has consistently surpassed these results without bariatric surgery.
Regulatory status
Currently in Phase 3 (TRIUMPH trials). If results replicate Phase 2, FDA application could be submitted in 2026–2027.
Adverse effects profile (Phase 2)
- Nausea: ~42% (dose-dependent)
- Diarrhea: ~26%
- Vomiting: ~20%
- Lean mass reduction: observed in some participants (body composition study ongoing)
Muscle mass loss with all GLP-1/GIP agonists is an active research area; resistance exercise and adequate protein intake are recommended during any weight loss protocol.
For educational reference only. For research use only. Retatrutide is not approved. Not available outside authorized clinical trials.
Reported protocol (research reference)
| Vial sizes | 5 mg, 10 mg |
|---|---|
| Reported dose | In Phase 2 trials: escalation from 1 mg/week to 12 mg/week over 24 weeks. Outside clinical trials, no approved protocol exists. |
| Half-life | Approximately 6 days — weekly dosing. |
| FDA status | Investigational |