What it is: An investigational weekly injection engineered to simultaneously activate three hormone receptor systems - GLP-1, GIP, and glucagon - for metabolic regulation.
Research suggests: Phase 3 trials (the TRIUMPH program) have shown some of the largest weight reductions of any compound studied in controlled trials, building on earlier Phase 2 findings.
Best for: Obesity and advanced metabolic researchers
Key thing to know: Not yet approved. Phase 3 trials are ongoing, with a regulatory decision anticipated in the 2026-2027 timeframe, and the long-term safety profile is still being characterized.
What is Retatrutide?
Retatrutide is an investigational triple incretin receptor agonist — a single molecule engineered to activate three hormone receptor systems: GLP-1 (glucagon-like peptide-1), GIP (glucose-dependent insulinotropic polypeptide), and the glucagon receptor, through different but potentially synergistic mechanisms. Retatrutide is not approved and is in Phase 3 clinical trials (the TRIUMPH program) conducted by Eli Lilly.
Researchers have studied retatrutide mainly for weight loss and metabolic health, with added interest in non-alcoholic fatty liver disease (NAFLD/NASH), given glucagon's effects on hepatic fat metabolism. Phase 3 data has continued to show weight reductions exceeding any approved anti-obesity medication, building on the record-setting Phase 2 findings first reported in 2023.
How it works.
In research, the proposed mechanism has several parts.
Building on tirzepatide: Retatrutide builds on the dual mechanism of tirzepatide by adding a third pathway: glucagon receptor co-activation. GLP-1 receptor activation reduces appetite and slows gastric emptying. GIP receptor activation enhances insulin secretion and may improve fat tissue insulin sensitivity.
The GLP-1/GIP base: Together these two pathways form the foundation that already makes tirzepatide more effective than GLP-1 monotherapy.
The glucagon addition: The glucagon receptor addition is the mechanistic bet that distinguishes retatrutide. Glucagon is usually thought of as a blood-sugar-raising hormone, but in research, glucagon receptor activation in the liver appears to increase energy expenditure and accelerate hepatic fat breakdown (lipolysis) — adding a thermogenic, fat-mobilizing component to the appetite suppression and insulin sensitization from GLP-1 and GIP.
In plain terms: Think of it as adding a fat-burning accelerator on top of the other two pathways' appetite and blood-sugar effects. The hypothesis, being tested in Phase 3, is that all three mechanisms together produce synergistic effects beyond any dual combination. Phase 3 data is consistent with this, though broader confirmation is still required.
What the research shows.
The research evidence breaks down as follows.
Phase 3 (TRIUMPH): Phase 3 trials (the TRIUMPH program) have reported record-setting weight reductions, among the largest seen for any anti-obesity compound in controlled trials. These build on the earlier Phase 2 trial data published in 2023, which first established retatrutide as a record-setting candidate.
Phase 2 context: Phase 2 trials are designed mainly to establish dosing ranges and preliminary efficacy signals, not the definitive safety and efficacy evidence Phase 3 delivers. The Phase 2 data on retatrutide is therefore promising but not yet confirmatory. Phase 3 trials are ongoing, with a regulatory decision anticipated in the 2026-2027 timeframe.
Additional signals: Additional signals of interest from Phase 2 data include reductions in liver fat content, consistent with the expected hepatic effects of glucagon receptor activation, and favorable effects on lipid markers. These findings are being examined further in dedicated Phase 3 substudies.
Biomarkers to review first.
Research protocols for retatrutide typically reference the following biomarkers as baseline context. The addition of glucagon receptor agonism makes liver function monitoring particularly relevant alongside the standard metabolic panel.
See the full lab testing guide →What it's commonly researched with.
Retatrutide appears primarily in comparison research alongside semaglutide and tirzepatide, where investigators examine the incremental contribution of the glucagon receptor pathway to metabolic outcomes. These are comparison studies, not combination protocols, all three compounds act on overlapping pathways and are not researched in combination with each other.
Goals & biomarkers connected to this compound.
Go deeper
How retatrutide's triple-receptor approach fits within the broader class of GLP-1, dual, and triple agonists.
Read Research →