Retatrutide clinical trial results mark a new ceiling for GLP-1 class drugs. In TRIUMPH-1, participants with severe obesity lost an average of 30.3% of body weight over 104 weeks — bariatric-level outcomes. Access requires a provider-issued prescription and evaluation at TelosRX.
Three Phase 3 trials have now reported retatrutide data. Here's what each found, what the numbers mean in context, and what remains unknown as additional trials run through 2026.
What Retatrutide Is: Triple-Agonism Explained
Retatrutide is a once-weekly injectable peptide developed by Eli Lilly. It activates three receptors simultaneously: GLP-1, GIP, and glucagon.
GLP-1 receptors reduce appetite and slow gastric emptying. GIP receptors amplify that effect and improve glucose metabolism. The glucagon receptor drives direct fat oxidation in the liver and boosts energy expenditure — an action neither semaglutide nor tirzepatide shares.
Retatrutide is not FDA-approved. It is an investigational compound still in Phase 3 development. Any compounded retatrutide available through a licensed telehealth provider is prepared under federal compounding regulations, subject to evaluation by a licensed provider before any prescription can be issued.
TRIUMPH-1: The Phase 3 Flagship Trial
TRIUMPH-1 enrolled adults with obesity (BMI ≥30) or overweight with at least one weight-related condition. It was a 104-week, randomized, double-blind, placebo-controlled study — the standard design for weight-loss drug evaluation.
Top-line results were announced in May 2026. Key findings:
| Dose | Population | Duration | Mean % Body Weight Lost |
|---|---|---|---|
| Retatrutide 12 mg | Severe obesity (BMI ≥35) | 104 weeks | 30.3% (~85 lbs avg) |
| Retatrutide 12 mg | All obesity (BMI ≥30) | 104 weeks | ~28% |
| Retatrutide 9 mg | All obesity (BMI ≥30) | 104 weeks | ~26% |
| Placebo | All obesity | 104 weeks | <3% |
The 30.3% average at 104 weeks is notable because Roux-en-Y gastric bypass typically achieves 25–35% total body weight loss. TRIUMPH-1 is the first Phase 3 pharmacological trial to reach that range consistently in people with severe obesity.
Full peer-reviewed publication of TRIUMPH-1 data was pending as of this writing. The results above are from Eli Lilly's topline announcement; complete data are expected in a peer-reviewed journal later in 2026.
TRIUMPH-4: Retatrutide and Knee Osteoarthritis
TRIUMPH-4 took a specific angle: 445 adults with obesity or overweight plus moderate-to-severe knee osteoarthritis. Results were announced in December 2025.
Participants on retatrutide lost up to 28.7% of body weight at 68 weeks, averaging 32.3 kg (71.2 lbs). The trial also assessed knee pain as a co-primary endpoint — the first Phase 3 obesity trial to simultaneously measure a musculoskeletal outcome alongside weight loss.
Obesity and knee osteoarthritis reinforce each other: each additional unit of BMI places roughly four additional units of force on the knee joint during walking. A drug that addresses both simultaneously represents a different kind of clinical outcome than weight loss alone.
TRANSCEND-T2D-1: Results in Type 2 Diabetes
Published in March 2026, TRANSCEND-T2D-1 enrolled adults with type 2 diabetes taking standard background medications. At 40 weeks on retatrutide 12 mg, participants lost an average of 16.8% of body weight.
That's lower than the TRIUMPH obesity-only results — consistent with how GLP-1 class drugs generally perform in T2D populations. For comparison, semaglutide 2.4 mg in the STEP-2 trial (T2D) showed 9.6% at 68 weeks. Tirzepatide in SURMOUNT-2 (T2D) showed approximately 14.7% at 72 weeks.
HbA1c reductions were also reported as part of TRANSCEND-T2D-1, though complete glycemic data were not available in peer-reviewed form at the time of this writing.
Retatrutide vs Tirzepatide vs Semaglutide: What the Numbers Show
No head-to-head trial has compared all three drugs directly. These are Phase 3 primary endpoint comparisons across separate studies with different designs and durations.
| Drug | Receptors Activated | Phase 3 Peak Weight Loss | Trial Duration | FDA Status |
|---|---|---|---|---|
| Semaglutide 2.4 mg (Wegovy) | GLP-1 | ~15% | 68 weeks | FDA-approved (2021) |
| Tirzepatide 15 mg (Zepbound) | GLP-1 + GIP | ~20.9% | 72 weeks | FDA-approved (2023) |
| Retatrutide 12 mg | GLP-1 + GIP + Glucagon | 30.3% | 104 weeks | Not FDA-approved |
The 104-week duration matters. Comparing 30.3% at 104 weeks to 20.9% at 72 weeks is not a direct comparison — weight loss with GLP-1 class drugs continues to accrue over time. The TRIUMPH-1 duration is simply longer than the pivotal semaglutide and tirzepatide trials.
For a deeper look at the current compounded GLP-1 options, see our tirzepatide vs semaglutide comparison and our retatrutide overview article.
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Safety Profile: What Phase 3 Reported
The adverse event profile across TRIUMPH trials was consistent with the GLP-1 drug class. No new safety signals emerged in published topline data.
- Nausea: Most common adverse event, typically mild-to-moderate and concentrated during dose titration
- Vomiting and diarrhea: Reported at lower rates than nausea
- Constipation: Dose-dependent; more common at 12 mg
- Heart rate elevation: A mean increase of approximately 3–4 bpm, attributed to glucagon receptor activity
- Injection-site reactions: Mild in most participants
Serious adverse events occurred at rates comparable to placebo in TRIUMPH-1 topline data. Pancreatic and thyroid safety signals are consistent with the broader GLP-1 drug class. A dedicated cardiovascular outcomes trial is ongoing.
The Phase 2 retatrutide trial, published in the New England Journal of Medicine in 2023, reported a broadly consistent safety profile with GI events as the primary adverse events and dose-related in frequency.
What Still Isn't Known: Ongoing Phase 3 Trials
Seven additional Phase 3 trials were ongoing as of mid-2026, covering sleep apnea, cardiovascular outcomes, MASLD/NASH, and additional obesity subgroups. Eli Lilly had not announced an FDA submission date as of this writing.
Retatrutide remains not FDA-approved. Active trial registrations can be found at ClinicalTrials.gov.
Frequently Asked Questions
What were the TRIUMPH-1 retatrutide trial results?
TRIUMPH-1 found that retatrutide 12 mg produced an average of 30.3% body weight loss at 104 weeks in adults with severe obesity (BMI ≥35). In the broader obesity population (BMI ≥30), the 12 mg dose produced approximately 28% weight loss. The trial was randomized, double-blind, and placebo-controlled. Full peer-reviewed data are pending publication.
Is retatrutide FDA-approved?
No. Retatrutide is not FDA-approved as of July 2026. It is an investigational compound in Phase 3 clinical development by Eli Lilly. Compounded retatrutide available through telehealth providers is not FDA-approved, is prepared under federal compounding regulations, and is subject to evaluation by a licensed provider before any prescription is issued.
How does retatrutide compare to semaglutide and tirzepatide?
In Phase 3 trials, retatrutide at 12 mg achieved approximately 30.3% weight loss at 104 weeks. Tirzepatide at 15 mg achieved approximately 20.9% at 72 weeks. Semaglutide at 2.4 mg achieved approximately 15% at 68 weeks. These were separate trials with different designs and durations, not head-to-head comparisons. Retatrutide adds glucagon receptor agonism that the other two lack.
What are the side effects of retatrutide in Phase 3?
The most commonly reported side effects in TRIUMPH trials were gastrointestinal: nausea, vomiting, diarrhea, and constipation. A modest heart rate increase of approximately 3–4 bpm was observed, consistent with glucagon receptor activation. Serious adverse events occurred at rates comparable to placebo. Long-term cardiovascular safety data are being collected in an ongoing trial.
When will retatrutide be available as a prescription drug?
As of mid-2026, Eli Lilly had not announced an FDA submission date for retatrutide. Multiple Phase 3 trials remain ongoing. Commercial availability, if approved, is at minimum 1–2 years away. Compounded retatrutide may be available through licensed telehealth providers pending individual provider evaluation, but it is not the same as the drug under development by Lilly.
How does the TRIUMPH-4 trial differ from TRIUMPH-1?
TRIUMPH-4 enrolled adults with obesity or overweight who also had moderate-to-severe knee osteoarthritis, and it measured both weight loss and knee pain over 68 weeks. TRIUMPH-1 was a broader obesity trial at 104 weeks with no joint-specific co-endpoint. Both showed substantial weight loss in their populations.
TelosRX is LegitScript-certified. Compounded medications are not FDA-approved and are prepared under federal compounding regulations. Approval is subject to evaluation by a licensed provider; approval is not guaranteed. Individual results vary. TelosRX operates as an online-first, asynchronous telehealth service.
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