Triple GLP-1 / GIP / Glucagon Receptor Agonist
Retatrutide (LY3437943) is the first triple incretin receptor agonist in clinical development, simultaneously activating the GLP-1, GIP, and glucagon receptors. Developed by Eli Lilly, it was first disclosed at the American Diabetes Association 2022 Scientific Sessions and published in the New England Journal of Medicine in 2023. The compound represents a paradigm shift from dual agonism (tirzepatide) to triple agonism by incorporating glucagon receptor activity. The addition of glucagon receptor agonism introduces a critical thermogenic component absent in both selective GLP-1 agonists and dual GLP-1/GIP agonists. Glucagon receptor activation stimulates hepatic glycogenolysis and gluconeogenesis, promotes lipolysis in adipose tissue, and increases energy expenditure through thermogenesis — mechanisms that complement the appetite-suppressing effects of GLP-1R and GIPR activation. In the phase 2 TRIUMPH trial, the highest dose (12 mg weekly) produced a mean body weight reduction of 24.2% at 48 weeks — the largest weight loss ever observed with a single pharmacological agent. This surpassed tirzepatide's 22.5% at 72 weeks, achieved in a shorter timeframe, suggesting that triple agonism provides additive metabolic benefits beyond dual receptor engagement.
Simultaneously engages GLP-1, GIP, and glucagon receptors — the most comprehensive incretin receptor coverage in any single compound.
TRIUMPH trial showed 24.2% mean weight loss at 48 weeks — the highest of any monotherapy agent, achieved in a shorter timeframe than tirzepatide.
Glucagon receptor agonism increases resting energy expenditure through BAT activation and hepatic thermogenesis.
Phase 2 data showed dramatic reduction in liver fat content, with potential applications in NASH/MAFLD research.
HbA1c reductions of up to 2.16% in type 2 diabetes populations despite glucagon's hyperglycemic potential.
Significant improvements in triglycerides, total cholesterol, and LDL-C across dose levels.
Preferential loss of fat mass over lean mass, with evidence of visceral adipose tissue reduction.
Retatrutide engages three distinct class B GPCRs with calibrated relative potencies. GLP-1R agonism drives appetite suppression via hypothalamic POMC/CART neuron activation and delayed gastric emptying through vagal signaling. GIPR activation amplifies insulin secretion and may promote healthy adipocyte differentiation. The distinguishing feature — glucagon receptor agonism — activates hepatic adenylyl cyclase, increasing cAMP and PKA activity to stimulate glycogenolysis, gluconeogenesis, and fatty acid oxidation. The glucagon component is particularly significant for energy expenditure. Glucagon receptor activation in brown and beige adipose tissue increases uncoupling protein 1 (UCP1) expression, promoting non-shivering thermogenesis. In the liver, glucagon drives fatty acid beta-oxidation and ketogenesis while reducing de novo lipogenesis through AMPK pathway activation. This creates a fundamentally different metabolic profile from GLP-1-only compounds: while GLP-1 agonists primarily reduce energy intake, retatrutide simultaneously reduces intake and increases expenditure. The apparent paradox of administering a glucagon agonist in metabolic research is resolved by the concurrent GLP-1R and GIPR agonism, which provide sufficient insulin secretion stimulus to counterbalance glucagon's hyperglycemic effects. Clinical data confirm that net glycemic control improves despite glucagon receptor engagement, suggesting the incretin components dominate glucose regulation while the glucagon component drives independent effects on lipid metabolism and energy expenditure.
TRIUMPH phase 2 evaluating weight loss, body composition changes, and metabolic parameters across multiple dose levels.
Phase 2 CompletePhase 2 trial assessing glycemic control and metabolic outcomes in T2DM patients, demonstrating HbA1c reductions despite glucagon agonism.
Phase 2 CompleteEvaluating hepatic steatosis resolution and fibrosis outcomes via glucagon-driven hepatic fat oxidation.
Phase 2Planned phase 3 outcomes trial assessing MACE reduction and cardiovascular risk parameters.
PlannedMechanistic studies comparing resting energy expenditure changes between dual (GLP-1/GIP) and triple (GLP-1/GIP/glucagon) agonism.
ActivePhase 3 study evaluating improvement in apnea-hypopnea index (AHI) in participants with obesity and moderate-to-severe OSA.
Phase 3| Period | Dose | Frequency | Notes |
|---|---|---|---|
| 1–4 | 0.5 mg | Once weekly | Low-dose initiation — GI tolerability assessment |
| 5–8 | 2 mg | Once weekly | First escalation step |
| 9–12 | 4 mg | Once weekly | Second escalation step |
| 13–16 | 8 mg | Once weekly | Target maintenance for some protocols |
| 17+ | 12 mg | Once weekly | Maximum studied dose — 24.2% weight loss in TRIUMPH |
While tirzepatide is a dual GLP-1/GIP agonist, retatrutide adds glucagon receptor agonism as a third mechanism. This produces greater weight loss (24.2% vs 22.5%) in a shorter timeframe (48 vs 72 weeks). The glucagon component uniquely increases energy expenditure through thermogenesis, whereas tirzepatide works primarily through appetite reduction and improved metabolic signaling. However, retatrutide remains investigational, while tirzepatide has FDA approval.
Glucagon receptor activation increases hepatic fatty acid oxidation, promotes BAT thermogenesis, and stimulates energy expenditure — effects absent in GLP-1 or GLP-1/GIP agonists. While glucagon raises blood glucose in isolation, the concurrent GLP-1 and GIP agonism provides sufficient insulin secretion to offset hyperglycemia. The net effect is enhanced fat loss through the combination of reduced caloric intake (GLP-1/GIP) and increased caloric expenditure (glucagon).
Reconstitute lyophilized retatrutide with bacteriostatic water at 1–2 mg/mL. Inject solvent slowly against the vial wall, swirl gently, and allow full dissolution. The solution should be clear and colorless. Store reconstituted peptide at 2–8°C and use within 28 days. Do not freeze the reconstituted solution.
As of 2025, retatrutide is in multiple phase 3 clinical trials (TRIUMPH program). Phase 2 results published in NEJM showed 24.2% weight reduction at the 12 mg dose. Phase 3 trials are evaluating obesity, type 2 diabetes, NASH, and obstructive sleep apnea outcomes. No regulatory approval has been granted yet.
In theory, glucagon receptor activation promotes hepatic glucose output. However, clinical data consistently show net improvement in glycemic control because the GLP-1 and GIP components stimulate insulin secretion that outweighs glucagon's hyperglycemic action. In the phase 2 T2DM trial, HbA1c decreased by up to 2.16%, confirming that the incretin effects dominate glucose homeostasis.
Need help choosing a peptide?
Try the AI Coach →