Key Takeaways
- TRIUMPH-4 was the first Phase 3 readout for retatrutide, announced by Eli Lilly on December 11, 2025 — a historically significant milestone in the drug’s development. Retatrutide remains investigational and is not FDA-approved.
- The trial studied retatrutide 12 mg in adults with obesity and knee osteoarthritis over 68 weeks, reporting 28.7% mean weight loss versus 2.1% for placebo.
- Knee osteoarthritis pain was reduced by 75.8% among participants, a substantial secondary finding linking weight loss to joint pain relief.
- Approximately 95% of participants achieved at least 5% weight loss, a threshold generally considered clinically meaningful.
- TRIUMPH-4 data will support Eli Lilly’s planned New Drug Application, expected in Q4 2026, but does not represent FDA approval — retatrutide remains accessible only through clinical trial enrollment.
- The pain-reduction findings raise the possibility that retatrutide could eventually be studied for indications beyond weight management alone, though this is not yet established or approved.
TRIUMPH-4 findings are described here for informational purposes only. Retatrutide has not been approved for any indication.
On December 11, 2025, Eli Lilly released topline results from TRIUMPH-4, marking the first Phase 3 trial readout in retatrutide’s entire development program. The trial holds particular significance not just because it was first, but because of its design: rather than studying weight loss alone, TRIUMPH-4 examined retatrutide in adults who had both obesity and knee osteoarthritis, a common and painful comorbidity of excess weight. Before reviewing the data, it’s essential to restate the core fact governing this entire drug program: retatrutide is investigational and has not been approved by the FDA or any other regulatory authority as of July 2026. TRIUMPH-4’s results are a step toward a possible future approval, not a treatment recommendation, and the drug remains accessible only through registered clinical trials.
This article breaks down what TRIUMPH-4 tested, the weight-loss and joint-pain results, how they compare to other retatrutide trials, and what this milestone readout meant for the broader retatrutide development timeline.
Why TRIUMPH-4 Mattered as the First Readout
Retatrutide’s Phase 3 program includes several parallel trials, each targeting a different population or endpoint: TRIUMPH-1 (general obesity), TRIUMPH-2 (obesity with type 2 diabetes), TRIUMPH-3 (obesity with cardiovascular disease), and TRIUMPH-4 (obesity with knee osteoarthritis). TRIUMPH-4 was the first of these to report results, arriving on December 11, 2025, months before TRIUMPH-1’s topline data in May 2026. As the earliest large-scale confirmation of retatrutide’s real-world effect size, it gave the field its first solid look at whether the drug’s Phase 2 promise would hold up in a bigger, longer trial.
| Trial | Population Focus | Readout Date | Status |
|---|---|---|---|
| TRIUMPH-4 | Obesity + knee osteoarthritis | Dec 11, 2025 | Complete |
| TRANSCEND-T2D-1 | Type 2 diabetes | March 19, 2026 (topline); June 2026 (Lancet) | Complete |
| TRIUMPH-1 | General obesity | May 21, 2026 | Complete |
| TRIUMPH-2 | Obesity + type 2 diabetes | Q3–Q4 2026 | Ongoing |
| TRIUMPH-3 | Obesity + cardiovascular disease | Q3–Q4 2026 | Ongoing |
Trial Design
TRIUMPH-4 enrolled approximately 445 participants with both obesity and knee osteoarthritis and followed them for 68 weeks on the 12 mg dose of retatrutide compared with placebo, according to Eli Lilly’s TRIUMPH-4 topline release.
| Design Element | Detail |
|---|---|
| Population | Adults with obesity and knee osteoarthritis |
| Approximate N | 445 |
| Duration | 68 weeks |
| Dose studied | 12 mg once-weekly subcutaneous injection |
| Comparator | Placebo |
| Endpoints | Body weight change; knee osteoarthritis pain score |
This dual-endpoint design — weight loss plus a specific comorbidity outcome — reflects a broader trend in obesity drug development: measuring not just pounds lost, but the downstream health consequences of that weight loss.
Weight-Loss Results
TRIUMPH-4’s weight-loss findings were consistent with what would later be confirmed at larger scale in TRIUMPH-1. At the 12 mg dose, participants lost a mean of 28.7% of body weight over 68 weeks, compared with just 2.1% in the placebo group.
| Outcome | Retatrutide 12 mg | Placebo |
|---|---|---|
| Mean weight loss (68 weeks) | 28.7% | 2.1% |
| Participants achieving ≥5% weight loss | ~95% | Substantially lower |
The near-universal rate of participants reaching at least 5% weight loss — approximately 95% — is a notable data point, since a 5% threshold is widely used in clinical literature as the benchmark for a “clinically meaningful” weight-loss response. Achieving this in the overwhelming majority of a trial population is a strong efficacy signal.
| Trial Comparison | Dose | Duration | Mean Weight Loss |
|---|---|---|---|
| TRIUMPH-4 | 12 mg | 68 weeks | 28.7% |
| TRIUMPH-1 | 12 mg | 80 weeks | 28.3% |
The close alignment between TRIUMPH-4’s 28.7% (at 68 weeks) and TRIUMPH-1’s 28.3% (at 80 weeks) gave researchers early confidence that the drug’s effect size was reproducible across different trial populations — an important signal ahead of TRIUMPH-1’s later, larger readout.
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Knee Osteoarthritis Pain Results
The joint-pain findings were the distinguishing feature of TRIUMPH-4. Participants reported a 75.8% reduction in knee osteoarthritis pain, a substantial improvement that adds an important secondary dimension to the weight-loss story: for people whose knee pain is driven or worsened by excess body weight, the magnitude of weight loss produced by retatrutide appears to translate into meaningful joint symptom relief.
| Secondary Outcome | Result |
|---|---|
| Knee osteoarthritis pain reduction | 75.8% |
This finding sits within a well-established clinical relationship: knee osteoarthritis is mechanically and inflammatorily linked to excess body weight, and substantial weight loss — whether from surgery or medication — has previously been shown to reduce joint loading and pain in people with this comorbidity. TRIUMPH-4 is notable for quantifying that relationship specifically for retatrutide at a dose and duration relevant to its likely future clinical use.
How TRIUMPH-4 Compares to Retatrutide’s Other Trials
| Trial | Focus | Duration | Weight Loss (top dose) | Key Secondary Finding |
|---|---|---|---|---|
| TRIUMPH-4 | Obesity + knee OA | 68 weeks | 28.7% | 75.8% knee pain reduction |
| TRIUMPH-1 | General obesity | 80 weeks | 28.3% | 45.3% achieved ≥30% weight loss |
| TRANSCEND-T2D-1 | Type 2 diabetes | 40 weeks | 11.5%–16.8% | HbA1c reduction up to 2.0% |
Weight loss in TRIUMPH-4 and TRIUMPH-1 landed within roughly half a percentage point of each other despite different populations and slightly different trial durations — a pattern that suggests retatrutide’s weight-loss effect is fairly consistent across obesity populations without major diabetes-related comorbidities. This is a helpful comparison for readers wondering how retatrutide’s effect size holds up across different patient populations.
What TRIUMPH-4 Means Going Forward
TRIUMPH-4’s results, alongside data from TRIUMPH-1 and TRANSCEND-T2D-1, are expected to form part of Eli Lilly’s New Drug Application, anticipated in Q4 2026. If the application is accepted and reviewed on the projected timeline, FDA acceptance would occur around Q1 2027, with a potential approval decision in late 2027 and a possible commercial launch in Q1–Q2 2028.
The knee osteoarthritis findings may also open the door to future indication-specific study, though no such expanded indication has been pursued or approved at this time. As with every other retatrutide trial, TRIUMPH-4’s results describe investigational data — they do not constitute approval for any use, including weight loss or joint pain, and the only legal way to access retatrutide remains enrollment in an authorized clinical trial through ClinicalTrials.gov.
For readers comparing this drug class overall, it’s worth understanding how approved options like tirzepatide and semaglutide-based drugs such as Wegovy currently address obesity-related comorbidities, since those remain the only regulator-approved choices while retatrutide’s review process continues.
FAQ
What was TRIUMPH-4 and why was it significant?
TRIUMPH-4 was retatrutide’s first Phase 3 trial readout, announced December 11, 2025. It studied obesity and knee osteoarthritis together, making it historically important as the earliest large-scale confirmation of the drug’s effect size ahead of later trials like TRIUMPH-1.
How much weight did participants lose in TRIUMPH-4?
Participants on the 12 mg dose lost a mean of 28.7% of body weight over 68 weeks, compared with 2.1% for placebo, according to Eli Lilly’s topline release.
Did retatrutide help with knee pain specifically?
Yes. TRIUMPH-4 reported a 75.8% reduction in knee osteoarthritis pain among participants, a substantial secondary finding tied to the trial’s weight-loss results.
Is retatrutide now approved for knee osteoarthritis?
No. Retatrutide has not been approved for any indication, including obesity or knee osteoarthritis. TRIUMPH-4 is trial data supporting a potential future New Drug Application, not a marketing approval.
How does TRIUMPH-4 compare to TRIUMPH-1?
The two trials reported very similar weight-loss results (28.7% vs. 28.3%) despite different populations and slightly different durations, suggesting a consistent effect size across obesity populations without major diabetes-related comorbidities.
Medical disclaimer: Retatrutide is an investigational drug not approved by the FDA or any other regulatory authority as of July 2026. It is available only through enrollment in authorized clinical trials. This article is for informational purposes only and does not constitute medical advice, endorsement, or a recommendation to obtain retatrutide outside of a registered clinical trial. Speak with your healthcare provider about currently approved weight-loss treatments. Content published by WeightLossInjections.com.
