What Is Retatrutide (GLP-3 RT)?
Retatrutide is an investigational triple agonist peptide developed by Eli Lilly that simultaneously targets GLP-1 receptors, GIP receptors, and glucagon receptors (GCGR). This tri-agonist profile distinguishes it from Tirzepatide (dual GIP/GLP-1) and single-target GLP-1 agonists like Semaglutide. As of 2025, Retatrutide is in Phase 3 clinical trials, with Phase 2 data showing particularly striking weight reduction outcomes.
The Triple Agonist Mechanism
GLP-1 + GIP Pathway (shared with Tirzepatide)
As with Tirzepatide, GLP-1R agonism reduces appetite, slows gastric emptying, and enhances glucose-stimulated insulin secretion. GIPR agonism adds complementary metabolic effects and may enhance the central appetite-suppressing signals.
The Glucagon Receptor Pathway โ The Key Difference
The addition of GCGR agonism is what uniquely defines Retatrutide's mechanism. Glucagon receptor activation increases hepatic glucose output and stimulates energy expenditure by driving fatty acid oxidation in the liver and increasing thermogenesis. While chronic high-dose glucagon agonism can be problematic in isolation, in combination with GLP-1R agonism (which suppresses glucagon and reduces appetite), the net effect in preclinical and clinical research has been substantially enhanced fat loss without the hyperglycemic risk.
Phase 2 Clinical Data Overview
| Endpoint | Retatrutide 12mg (48 wks) | Tirzepatide 15mg (72 wks) |
|---|---|---|
| Mean weight reduction | ~24.2% | ~22.5% |
| Subjects achieving โฅ20% loss | ~83% | ~57% |
| HbA1c reduction (T2D) | Significant | Significant |
| Liver fat reduction | Pronounced (NASH studies) | Moderate |
Phase 2 data from the TRIUMPH-1 study (NEJM, 2023) showed Retatrutide produced the highest body weight reductions yet observed in an incretin-class Phase 2 trial. These results drove rapid advancement to Phase 3.
Triple vs. Dual Agonism โ Key Research Questions
The central research question for GLP-3 RT vs. GLP-2 TRZ is: does the additional glucagon receptor agonism produce meaningful additional metabolic benefit beyond dual GIP/GLP-1 agonism? Phase 2 data is encouraging, but Phase 3 data will be critical for establishing the clinical benefit profile.
Storage & Handling
Store lyophilized Retatrutide at โ20ยฐC. Protect from light. After reconstitution, store at 2โ8ยฐC and use within 30 days.
For research use only. Not for human or animal use. Order GLP-3 RT here.