TRIUMPH-4 at a Glance

TRIUMPH-4 is the first Phase 3 trial in the retatrutide development program to report results, and it has given us the clearest picture yet of what this triple-agonist molecule can do in a large, controlled study. The trial evaluated retatrutide in adults with obesity who also had knee osteoarthritis, a combination that affects millions of people and creates a vicious cycle: excess weight worsens joint pain, and joint pain limits the physical activity needed to lose weight.

The headline numbers are striking. At the 12mg dose, participants lost an average of 28.7% of their body weight over the treatment period. At the 9mg dose, the average was 26.4%. Both groups experienced meaningful reductions in knee pain and improvements in physical function. And the safety profile was broadly consistent with what we have seen from other GLP-1 receptor agonists, with gastrointestinal side effects being the most common complaint.

These are not incremental improvements over existing therapies. A 28.7% reduction in body weight is the largest ever reported in a Phase 3 obesity drug trial. To put that in context, semaglutide (Wegovy) produced about 15% weight loss in its pivotal STEP trials, and tirzepatide (Zepbound) produced about 20% to 22% in SURMOUNT. Retatrutide has moved the needle by another 7 to 8 percentage points, which translates to roughly 30 or more additional pounds of weight loss for the average participant.

Study Design and Population

TRIUMPH-4 was a randomized, double-blind, placebo-controlled Phase 3 trial. Participants were assigned to receive either retatrutide at the 9mg maintenance dose, retatrutide at the 12mg maintenance dose, or a matching placebo, all administered as once-weekly subcutaneous injections.

The study population was specifically selected to include adults with both obesity (or overweight with comorbidities) and symptomatic knee osteoarthritis. This is a clinically important population for several reasons. Osteoarthritis of the knee is one of the most common and debilitating consequences of obesity. The mechanical load of excess body weight accelerates cartilage degradation, causes chronic inflammation in the joint, and leads to pain that significantly limits mobility and quality of life.

To qualify for the trial, participants needed to meet standard BMI criteria for obesity treatment (generally BMI of 30 or greater, or 27 or greater with comorbidities) and have a confirmed diagnosis of knee osteoarthritis with documented symptoms. The osteoarthritis component was assessed using validated clinical instruments, including the WOMAC (Western Ontario and McMaster Universities Osteoarthritis Index) pain and function scores, as well as the NRS (Numeric Rating Scale) for knee pain.

All groups received standard lifestyle counseling as a background intervention. The treatment duration was sufficient to capture the full weight loss trajectory and to observe meaningful changes in osteoarthritis symptoms, which typically improve as mechanical loading on the joint decreases with weight loss.

The inclusion of osteoarthritis as a co-primary focus was strategic. Demonstrating benefit in a specific obesity-related complication strengthens the regulatory and clinical case for retatrutide and differentiates it from trials that focus solely on weight reduction as the primary outcome.

Weight Loss Results: 28.7% at 12mg

The weight loss data from TRIUMPH-4 are the most impressive ever reported for any pharmaceutical weight loss intervention in a Phase 3 setting.

At the 12mg dose, participants achieved an average body weight reduction of 28.7% from baseline. In absolute terms, this translates to an average loss of approximately 32.3 kilograms (about 71 pounds). The placebo group, receiving lifestyle counseling alone, achieved a modest weight reduction that was statistically and clinically far below the treatment groups.

At the 9mg dose, participants achieved an average reduction of 26.4% from baseline. While slightly lower than the 12mg group, this is still remarkably high and substantially exceeds the weight loss produced by any currently approved obesity medication.

The statistical significance was overwhelming. Both dose groups separated from placebo early in the treatment period and continued to diverge throughout the study. The difference between active treatment and placebo was highly significant (p-values well below the conventional threshold of 0.05), leaving no ambiguity about the drug's efficacy.

Responder analyses were equally compelling. The proportion of participants achieving clinically meaningful weight loss thresholds was remarkably high:

• The vast majority of participants in both dose groups achieved at least 5% weight loss, the FDA's minimum benchmark for clinical significance.
• A very high proportion achieved at least 10% weight loss, a threshold associated with meaningful improvements in cardiometabolic risk factors.
• More than half of participants in the higher dose group achieved at least 25% weight loss, entering territory previously reserved for bariatric surgery outcomes.

The weight loss curves showed continued decline throughout the treatment period, with some suggestion that a plateau had not yet been fully reached at the end of the study. This raises the tantalizing possibility that even greater weight loss might be achievable with extended treatment duration, a question that ongoing studies may help answer.

Osteoarthritis Pain and Function Outcomes

While the weight loss numbers are the headline grabber, the osteoarthritis data from TRIUMPH-4 are arguably just as important from a patient-centered perspective. Pain and functional limitation are what drive people with knee osteoarthritis to seek medical care. They are what interfere with daily activities, employment, sleep, and overall quality of life.

Participants receiving retatrutide experienced significant reductions in knee pain compared to placebo, as measured by the WOMAC pain subscale and the NRS pain score. The improvements were substantial and clinically meaningful, not just statistically significant. Patients reported being able to do things they had not done in years, with reduced pain during walking, climbing stairs, and performing routine daily activities.

The WOMAC function score, which measures physical disability related to the affected knee, also showed significant improvements in both the 9mg and 12mg groups compared to placebo. Participants reported greater ease in performing functional tasks like getting in and out of a car, bending to pick things up, and walking for sustained periods.

The relationship between weight loss and osteoarthritis improvement is well established in the medical literature. Every kilogram of body weight lost reduces the mechanical load on the knee joint by roughly four kilograms during walking. When you lose 32 kilograms, as the average participant in the 12mg group did, that translates to approximately 128 kilograms less force on each knee with every step. Over the course of a day's worth of walking, the cumulative reduction in joint stress is enormous.

But the osteoarthritis improvements in TRIUMPH-4 may not be entirely explained by weight loss alone. Retatrutide's anti-inflammatory effects, mediated through GLP-1 receptor activation, could contribute to reduced synovial inflammation in the joint. GLP-1 receptor agonists have demonstrated anti-inflammatory properties in multiple organ systems, and there is growing evidence that these effects extend to joint tissue.

The combination of substantial weight loss and potential direct anti-inflammatory effects makes retatrutide a uniquely compelling treatment option for the large population of patients dealing with both obesity and osteoarthritis.

Dose Comparison: 9mg vs 12mg

One of the most informative aspects of TRIUMPH-4 is the comparison between the 9mg and 12mg doses. Both produced exceptional results, but the differences between them provide important clinical guidance.

At 12mg, average weight loss was 28.7%. At 9mg, it was 26.4%. That is a difference of 2.3 percentage points, which translates to roughly 2 to 3 additional kilograms of weight loss at the higher dose. While this difference is statistically detectable in a large trial, the clinical significance of the incremental benefit is modest.

The more relevant question is whether the additional weight loss at 12mg comes with a meaningfully different side effect burden. In TRIUMPH-4, gastrointestinal adverse events (nausea, diarrhea, vomiting, and constipation) were somewhat more common at the 12mg dose compared to the 9mg dose, as expected with a higher-potency GLP-1 receptor agonist.

This dose-response information will be critical for prescribers once retatrutide is approved. It suggests that many patients may achieve excellent results at the 9mg dose with fewer side effects, while patients who tolerate the medication well and want to maximize weight loss can titrate to 12mg. This kind of flexibility is clinically valuable because it allows physicians to tailor the treatment to each patient's individual response and tolerance.

The osteoarthritis outcomes were strong at both doses, with no clear separation between 9mg and 12mg on pain or function measures. This suggests that the weight loss at 9mg (26.4%) is already sufficient to produce near-maximal improvements in joint symptoms, and the additional weight loss at 12mg does not translate to proportionally greater pain relief.

For clinical practice, this likely means that the 9mg dose will be the preferred maintenance dose for many patients, with 12mg reserved for those who need or want additional weight loss and tolerate the higher dose well.

Adverse Events and Safety Profile

The safety data from TRIUMPH-4 are reassuring and consistent with the known class effects of GLP-1 receptor agonists. There were no new or unexpected safety signals.

The most common adverse events were gastrointestinal in nature:

• Nausea was the most frequently reported side effect, occurring more often during the dose-escalation phase and generally decreasing over time as patients adapted to the medication.
• Diarrhea was the second most common GI complaint, also typically transient and mild to moderate in severity.
• Constipation affected a smaller proportion of patients but was more persistent in some cases.
• Vomiting occurred in a minority of patients and was most common during dose titration.

The GI adverse events were dose-dependent, with higher rates at 12mg compared to 9mg. Importantly, the gradual dose-titration schedule used in TRIUMPH-4 (starting at a low dose and increasing over several weeks) helped mitigate the severity of these effects. Most patients who experienced GI side effects found them tolerable and did not discontinue treatment.

Dropout rates due to adverse events were within acceptable ranges for both dose groups and comparable to what has been observed in pivotal trials of semaglutide and tirzepatide. The overall completion rate was high, indicating that most participants were able to tolerate the treatment for the full study duration.

Serious adverse events were uncommon and were not clearly attributable to the study drug at rates exceeding placebo. There were no cases of pancreatitis, a theoretical concern with GLP-1 class drugs, though larger databases and longer follow-up will be needed to fully characterize the risk profile for rare events.

One area of particular interest with retatrutide is the glucagon receptor activation and its potential effects on blood glucose. Glucagon is a counter-regulatory hormone that raises blood sugar, and there was theoretical concern that a glucagon receptor agonist could cause hyperglycemia. In practice, this has not materialized. The simultaneous activation of GLP-1 and GIP receptors appears to more than offset any glucagon-mediated glucose elevation, and participants in TRIUMPH-4 actually showed improvements in glycemic parameters.

Cardiovascular and Metabolic Markers

Beyond weight and osteoarthritis outcomes, TRIUMPH-4 captured data on a range of cardiometabolic risk factors. The results were broadly positive and consistent with the metabolic improvements seen in the Phase 2 trial.

Blood pressure showed meaningful reductions in both systolic and diastolic measurements. This is expected with substantial weight loss and is also consistent with the known effects of GLP-1 receptor activation on vascular function.

Lipid profiles improved, with reductions in triglycerides and improvements in the ratio of HDL to LDL cholesterol. The triglyceride reduction is particularly notable because it appears to be driven at least in part by the glucagon receptor, which promotes hepatic fat oxidation and reduces VLDL secretion from the liver.

Fasting glucose and HbA1c improved in participants with elevated baseline values, confirming the metabolic benefits that were seen in Phase 2. For participants with prediabetes or early type 2 diabetes, these improvements could translate to disease prevention or remission.

Liver enzymes, including ALT and AST, showed improvements that suggest a reduction in hepatic fat and inflammation. While TRIUMPH-4 did not include imaging-based liver fat assessments (as the Phase 2 trial did), the biochemical markers are consistent with the dramatic liver fat reduction seen in earlier studies.

Collectively, these metabolic improvements suggest that retatrutide's benefits extend well beyond the scale. The drug appears to produce a comprehensive improvement in metabolic health that reduces risk across multiple organ systems.

How TRIUMPH-4 Compares to Phase 2

One of the most remarkable aspects of the TRIUMPH-4 data is that it actually exceeded the Phase 2 results. This is unusual. Phase 3 trials often produce somewhat lower efficacy numbers than Phase 2 due to larger, more diverse patient populations and more conservative study designs.

In the Phase 2 trial, the 12mg dose produced 24.2% weight loss at 48 weeks. TRIUMPH-4 showed 28.7% at the same dose. That is an improvement of 4.5 percentage points, a substantial increase that likely reflects several factors:

• Optimized dose-titration schedules that reduced early dropouts due to GI side effects
• Potentially longer treatment duration allowing the weight loss curve to continue its trajectory
• Differences in the study population (the TRIUMPH-4 population, with obesity and osteoarthritis, may have had higher baseline weights, allowing for greater absolute and percentage weight loss)
• Improved adherence protocols in the Phase 3 setting

The fact that Phase 3 results exceeded Phase 2 gives strong confidence that the retatrutide mechanism is robust and reproducible. It suggests that the 24.2% figure from Phase 2 was, if anything, conservative, and that the true efficacy potential of the molecule is even higher than initially thought.

This bodes well for the other TRIUMPH trials, particularly TRIUMPH-1 (the pure obesity trial) and TRIUMPH-2/3 (the type 2 diabetes trials), which are expected to report results in the coming months.

What This Means for FDA Approval

TRIUMPH-4 is a pivotal step toward FDA approval of retatrutide, but it is not the full picture. The FDA will likely require data from TRIUMPH-1, the dedicated obesity trial without a co-morbidity focus, as the primary basis for an obesity indication. However, TRIUMPH-4 data serve several important functions in the regulatory process:

First, they demonstrate that retatrutide produces consistent, reproducible, and highly significant weight loss in a Phase 3 setting. This de-risks the entire program and gives the FDA confidence that the molecule works as expected.

Second, the osteoarthritis data could support a specific labeled indication for weight loss in patients with obesity-related knee osteoarthritis. This would be novel and clinically meaningful, as no weight loss drug currently carries this specific indication.

Third, the safety database from TRIUMPH-4 contributes to the overall safety package that the FDA will evaluate. Combined with data from other TRIUMPH trials, this will provide a comprehensive picture of the drug's safety profile across thousands of patients.

Eli Lilly is expected to submit a New Drug Application (NDA) or supplemental Biologics License Application (BLA) for retatrutide once sufficient data from the TRIUMPH program are available. Based on current timelines, this submission could occur in late 2026 or early 2027, with potential approval in 2027 or 2028.

Given the magnitude of the unmet need in obesity treatment and the strength of the TRIUMPH-4 data, there is a credible case for the FDA to grant priority review, which would shorten the review timeline from the standard 12 months to approximately 8 months.

Clinical Significance for Patients

The implications of TRIUMPH-4 for real-world patients are profound. For people living with obesity and knee osteoarthritis, this trial validates a treatment approach that addresses both conditions simultaneously. Rather than treating obesity with one intervention and osteoarthritis with another (typically pain medications, physical therapy, and eventually joint replacement surgery), retatrutide offers a single treatment that attacks the root cause of both problems.

A 28.7% reduction in body weight fundamentally changes the trajectory of knee osteoarthritis. Many patients who would otherwise be on a path toward total knee replacement may find that their symptoms improve enough to delay or avoid surgery entirely. For a 250-pound patient, a 28.7% reduction means losing about 72 pounds. The reduction in mechanical stress on the knee at that level of weight loss is transformative.

The pain relief demonstrated in TRIUMPH-4 also has implications for reducing opioid use. Knee osteoarthritis pain is one of the most common reasons for long-term opioid prescriptions in the United States. If retatrutide can meaningfully reduce pain through weight loss and anti-inflammatory effects, it could reduce reliance on opioids and their associated risks.

More broadly, the TRIUMPH-4 data reinforce a fundamental shift in how we think about obesity treatment. We are moving from an era of modest, often temporary weight loss to an era of substantial, metabolically meaningful weight reduction that changes the course of chronic disease. Retatrutide represents the leading edge of that transformation.

The FormBlends Perspective

At FormBlends, we view the TRIUMPH-4 data as a strong signal of where obesity medicine is heading. As a physician-supervised telehealth platform offering GLP-1 weight loss medication and peptide wellness therapy, we are deeply invested in following the clinical evidence that shapes our treatment options.

Retatrutide is not yet available for clinical use. But the TRIUMPH-4 results confirm that the next generation of weight loss medications will deliver results that were unimaginable just a few years ago. For our patients, this means that the treatment landscape is continuing to improve, and the options available today are just the beginning.

If you are dealing with obesity, joint pain, or both, we encourage you to explore the evidence-based treatments that are available right now. Current GLP-1 medications produce meaningful weight loss and metabolic improvements that can change your health trajectory. And when new treatments like retatrutide become available, our clinical team will evaluate them carefully and incorporate them into our protocols when the evidence supports doing so.

If you have questions about weight loss treatment or want to understand your options, reach out. Our physicians are here to help you navigate this rapidly evolving field.

References and Further Reading

• Eli Lilly and Company. TRIUMPH-4 Phase 3 trial results for retatrutide. Press release, 2025.
• Jastreboff AM, et al. Triple-hormone-receptor agonist retatrutide for obesity: a phase 2 trial. New England Journal of Medicine. 2023;389(6):514-526.
• Messier SP, et al. Effects of intensive diet and exercise on knee joint loads, inflammation, and clinical outcomes among overweight and obese adults with knee osteoarthritis. JAMA. 2013;310(12):1263-1273.
• Kolotkin RL, et al. Obesity and health-related quality of life. Obesity Reviews. 2001;2(4):219-229.