Retatrutide Phase 3 Results: Up to 30.3% Weight Loss Across Lilly’s TRIUMPH Trials
Research & reporting note: This article summarizes publicly reported Phase 3 clinical trial results for Eli Lilly’s investigational drug retatrutide. NeuroPept Labs supplies retatrutide only as a research-use-only reference compound for laboratory study; it is not the Lilly product, is not for human consumption, and the clinical outcomes below are Lilly’s trial findings, not claims about any product sold here.
Retatrutide is a first-in-class GIP, GLP-1, and glucagon triple hormone-receptor agonist developed by Eli Lilly. Across its Phase 3 TRIUMPH program, the once-weekly investigational peptide produced average weight reductions of up to 30.3% (about 85 lbs) in obesity trials and up to 28.7% (?71.2 lbs) alongside 75.8% knee osteoarthritis pain relief — among the largest weight-loss figures reported for a pharmacological agent in a Phase 3 setting to date.
Key results at a glance
- Mechanism: first-in-class triple agonist — GIP + GLP-1 + glucagon receptors.
- TRIUMPH-1 (obesity): up to 28.3% weight loss at 80 weeks; 30.3% (85 lbs) at 104 weeks with no plateau.
- TRIUMPH-4 (obesity + knee OA): up to 28.7% (?71.2 lbs) and a 75.8% reduction in knee pain.
- Bariatric-level threshold: 45.3% of the highest-dose group achieved ?30% weight loss.
- Status: investigational — not yet approved; additional Phase 3 trials reading out through 2026.
- Research relevance: a leading model compound for studying multi-receptor incretin and glucagon signaling.
What is retatrutide?
Retatrutide is a once-weekly injectable peptide that simultaneously activates three metabolic hormone receptors:
- GLP-1 (glucagon-like peptide-1) — suppresses appetite, slows gastric emptying, and enhances glucose-dependent insulin secretion.
- GIP (glucose-dependent insulinotropic polypeptide) — supports glucose handling and amplifies the incretin response.
- Glucagon — the third, differentiating pathway, associated with increased energy expenditure and hepatic fat metabolism.
This triple-receptor design distinguishes it from single GLP-1 agonists such as semaglutide and from dual GIP/GLP-1 agonists such as tirzepatide. The added glucagon activity is widely credited with the unusually large weight reductions observed in the trials. For the mechanistic background, see our overviews of the GLP-1 incretin system and the GLP-1, GIP, and glucagon pathways.
TRIUMPH-1: the pivotal obesity trial
TRIUMPH-1 evaluated the peptide in adults with obesity or overweight and at least one weight-related comorbidity, without diabetes. It tested three once-weekly doses against placebo, with a primary endpoint at 80 weeks and an extension to 104 weeks. The dose-dependent results were striking:
| Dose (weekly) | Average weight loss | Pounds lost |
|---|---|---|
| 4 mg | 19.0% | 47.2 lbs |
| 9 mg | 25.9% | 64.4 lbs |
| 12 mg | 28.3% | 70.3 lbs |
| 12 mg (104-week extension) | 30.3% | 85.0 lbs |
Beyond the averages, several findings stood out in the highest-dose (12 mg) group:
- 45.3% achieved 30% or greater weight loss — a threshold historically associated with bariatric surgery.
- 65.3% reached a BMI below 30 (out of the obese range) by week 80.
- No weight-loss plateau was observed through 104 weeks, with continued reduction in the extension.
The absence of a plateau is a particularly notable research observation, since most weight-management agents show a leveling-off within the first year.
TRIUMPH-4: weight loss plus osteoarthritis pain relief
TRIUMPH-4 was a 68-week trial evaluating the two highest doses in adults with obesity or overweight and knee osteoarthritis, without diabetes. From an average baseline weight of 112.7 kg (248.5 lbs) and a BMI of 40.4, the results linked metabolic and joint outcomes:
- Weight loss of up to 28.7% (?32.3 kg / ?71.2 lbs) at 68 weeks.
- Knee pain reduced by up to 4.5 points on the WOMAC pain scale — a 75.8% reduction.
- Physical function significantly improved on validated measures.
- More than 1 in 8 retatrutide-treated participants were completely free of knee pain by the end of the trial.
TRIUMPH-4 is significant because it connects substantial weight loss to a measurable improvement in an inflammatory, weight-associated condition — expanding the research interest in triple agonism beyond weight alone.
The wider TRIUMPH program and diabetes data
TRIUMPH-1 and TRIUMPH-4 are part of a broader Phase 3 program spanning obesity, type 2 diabetes, and cardiovascular disease:
- TRIUMPH-2 and TRIUMPH-3 — evaluated the triple agonist in adults with obesity and type 2 diabetes or established cardiovascular disease, reporting positive topline weight and A1C results.
- Type 2 diabetes — a dedicated Phase 3 trial reported significant reductions in both A1C and body weight.
- Ongoing readouts — additional Phase 3 trials in obesity and diabetes are expected to complete through 2026.
Together these trials position it as a multi-indication candidate rather than a weight-loss agent alone, which is part of why it is so frequently referenced in metabolic research. The breadth also matters scientifically: a single molecule that shows benefit across obesity, joint pain, glycemic control, and — pending readouts — cardiovascular endpoints suggests the three targeted pathways touch several interconnected disease processes at once. For researchers, that raises questions the trials themselves cannot fully answer, such as how much of the joint-pain improvement is driven by weight loss versus a direct anti-inflammatory effect, or how the glucagon arm’s energy-expenditure contribution scales across different patient populations. Those open questions are precisely what keeps triple-agonist pharmacology an active area of laboratory study rather than a settled one, and they are the reason a well-characterized reference compound remains valuable for controlled mechanistic work.
How retatrutide compares
Placing retatrutide against the current generation of incretin therapies clarifies why its Phase 3 numbers drew attention:
| Agent | Class | Receptors | Reported Phase 3 weight loss |
|---|---|---|---|
| Semaglutide | Single agonist | GLP-1 | ~15% |
| Tirzepatide | Dual agonist | GIP + GLP-1 | ~20–23% |
| Retatrutide | Triple agonist | GIP + GLP-1 + glucagon | up to ~30% |
For deeper comparisons, see our research guides on Tirzepatide vs Retatrutide and Retatrutide vs Ozempic vs Mounjaro. The consistent theme is that each added receptor pathway has been associated with incremental weight-loss magnitude in the clinical literature.
Safety and tolerability context
In the reported trials, its safety profile was broadly consistent with the incretin drug class. The most common adverse events were gastrointestinal — nausea, diarrhea, vomiting, and constipation — generally mild to moderate and most frequent during dose escalation. As with all investigational agents, the complete safety picture will depend on peer-reviewed publication and regulatory review of the full datasets. Nothing in this summary should be interpreted as guidance for human use.
What this means for research
For laboratories studying metabolic signaling, retatrutide has become a reference triple agonist — a single molecule that engages the GIP, GLP-1, and glucagon receptors and therefore lets researchers probe how these pathways interact. Its role in research includes:
- Receptor pharmacology — characterizing simultaneous three-receptor activation versus single- or dual-agonist controls.
- Energy-expenditure models — isolating the contribution of the glucagon pathway.
- Comparative studies — benchmarking against tirzepatide and GLP-1 agonists.
NeuroPept Labs supplies research-grade Retatrutide 10mg and Retatrutide 30mg as lyophilized reference compounds with batch-specific third-party analytics, for in vitro and laboratory research only. These are not the Lilly clinical formulation and are not intended for human use.
Regulatory status
The compound remains investigational. It is not approved by the FDA or other regulators for any use, and the Phase 3 results summarized here are topline trial findings reported by Eli Lilly. Regulatory submissions and any approval decisions would follow completion and review of the full Phase 3 program. Primary sources include Lilly’s investor releases on the pivotal obesity trial and the osteoarthritis (TRIUMPH-4) trial.
Frequently asked questions
How much weight did retatrutide cause in Phase 3 trials?
In Lilly’s Phase 3 TRIUMPH program, retatrutide produced average weight loss of up to 28.3% (70.3 lbs) at 80 weeks in the TRIUMPH-1 obesity trial, rising to 30.3% (about 85 lbs) at 104 weeks, and up to 28.7% (?71.2 lbs) in the TRIUMPH-4 osteoarthritis trial. These are clinical trial results for an investigational drug, not outcomes for any research-use product.
What makes retatrutide different from Ozempic or Mounjaro?
Retatrutide is a triple agonist that activates GIP, GLP-1, and glucagon receptors. Ozempic (semaglutide) is a single GLP-1 agonist, and Mounjaro (tirzepatide) is a dual GIP/GLP-1 agonist. The added glucagon pathway is associated with retatrutide’s larger reported weight loss.
Did retatrutide help with osteoarthritis?
In the Phase 3 TRIUMPH-4 trial, retatrutide reduced knee osteoarthritis pain by up to 75.8% on the WOMAC pain scale and improved physical function, with more than one in eight participants completely free of knee pain by the end of the trial, alongside up to 28.7% weight loss.
Is retatrutide FDA approved?
No. Retatrutide is an investigational drug and is not approved by the FDA or other regulators. The Phase 3 results reported by Lilly are topline findings; regulatory review would follow completion of the full program.
What is retatrutide’s mechanism of action?
Retatrutide simultaneously activates three receptors: GLP-1 (appetite and insulin), GIP (glucose handling), and glucagon (energy expenditure and hepatic fat metabolism). This triple-agonist mechanism is the basis of its research and clinical interest.
Can I buy retatrutide for weight loss?
No. The retatrutide referenced by NeuroPept Labs is a research-use-only reference compound intended strictly for in vitro and laboratory investigation. It is not for human consumption, is not the approved or investigational clinical product, and nothing here is medical advice.