Retatrutide Knee Osteoarthritis Trial Results Phase 3 GZBJ

Retatrutide knee osteoarthritis trial results phase 3 GZBJ, known as TRIUMPH-4,[2] revealed impressive topline data from Eli Lilly.[1] At the highest 12 mg dose, patients with obesity and knee osteoarthritis achieved 28.7% average weight loss[1] alongside a 76% reduction in knee pain[1] after 68 weeks.[1][2] Both co-primary endpoints were met,[1] with improvements in physical function[1] and cardiovascular markers,[1] though gastrointestinal side effects and discontinuations remain key considerations.[1] Learn more about retatrutide phase 3 discontinuation rates and BMI correlations.

Introduction to Retatrutide Knee Osteoarthritis Trial Results Phase 3 GZBJ

Retatrutide knee osteoarthritis trial results phase 3 GZBJ mark a significant step in treating obesity-related joint pain. This phase 3 study, part of Eli Lilly's TRIUMPH program,[4] tested the drug in patients facing both weight challenges and knee issues.

What is Retatrutide and Its Mechanism of Action

Retatrutide, also called LY3437943,[2][3] is a triple hormone receptor agonist.[3] It activates GIP, GLP-1, and glucagon receptors[3] to promote weight loss, improve metabolism, and reduce inflammation.

This once-weekly subcutaneous injection[2][3] mimics gut hormones that regulate appetite, blood sugar, and energy use. In obesity trials, it has shown superior weight reduction compared to dual agonists like tirzepatide.

Overview of TRIUMPH-4 (J1I-MC-GZBJ) Trial

TRIUMPH-4 (NCT05931367)[2] is a randomized, double-blind, placebo-controlled phase 3 trial.[2] It enrolled adults with knee osteoarthritis and obesity or overweight, without diabetes.[2]

Topline results were announced on December 11, 2025,[1] showing the drug met all primary and key secondary endpoints.[1] Full peer-reviewed data is pending publication. ClinicalTrials.gov.[2] Check the retatrutide FDA approval tracker and is retatrutide FDA approved.

Why Knee Osteoarthritis in Obesity Patients Matters

Obesity worsens knee osteoarthritis by increasing joint stress and inflammation. Excess weight amplifies pain and limits mobility, creating a cycle hard to break with diet alone.

Up to 50% of knee OA patients are obese, per studies. Treatments targeting both weight and pain could transform care. Retatrutide addresses this dual burden directly.

Trial Design and Key Details of Phase 3 GZBJ Study

The retatrutide knee osteoarthritis trial results phase 3 GZBJ used a robust design to evaluate efficacy in real-world-like conditions. Patients followed diet and exercise alongside the drug.[2]

Study Population and Inclusion Criteria

Participants had BMI ≥30 (or ≥27 with comorbidities)[2] and knee OA confirmed by Kellgren-Lawrence Grade 2-3 X-rays.[2] They met American College of Rheumatology criteria,[2] with moderate-to-severe pain and no recent joint procedures.

Exclusion included diabetes, recent weight loss drugs, or plans for bariatric surgery. This focused on non-diabetic obese patients with symptomatic knee OA.

Doses Tested: 9 mg vs 12 mg vs Placebo

Highest doses were 12 mg and 9 mg weekly,[1][2] titrated gradually to minimize side effects. Placebo arm received identical injections.

Both active doses showed superiority over placebo on endpoints.[1] The 12 mg dose drove the strongest results.[1]

Duration, Status, and Sponsor (Eli Lilly)

The trial ran 68 weeks for primary endpoints,[1][2] with total duration around 77 weeks including screening.[2] It is completed, sponsored by Eli Lilly and Company.[2]

Positive topline data emerged in late 2025.[1] This fits into the broader TRIUMPH Phase 3 program with over 5,800 participants across indications.[1][4] Eli Lilly Investor Relations.[1]

Efficacy Results: Weight Loss and Pain Reduction in GZBJ Trial

Retatrutide knee osteoarthritis trial results phase 3 GZBJ highlighted transformative outcomes on weight and pain. Patients saw sustained benefits over 68 weeks,[1][2] exceeding prior phase 2 data.[3]

Co-Primary Endpoints: 28.7% Weight Loss and WOMAC Pain Score

At 12 mg, mean weight loss reached 28.7% (about 71.2 lbs or 32.3 kg),[1] far surpassing placebo's 2.1%.[1] This met the first co-primary endpoint convincingly.[1]

WOMAC pain subscale dropped 4.5 points from a baseline of ~6, equating to 75.8% improvement.[1] Placebo saw only ~40% decline,[1] confirming the second endpoint.[1]

Physical Function Improvements and Complete Pain Freedom

Physical function, also via WOMAC, improved significantly on both doses.[1] Post-hoc analysis showed 12.0% (12 mg) to 14.1% (9 mg) of patients achieved complete knee pain freedom, versus 4.2% on placebo.[1]

These gains suggest better daily activities and quality of life. One in eight patients became pain-free, a rare outcome in OA trials.

Cardiovascular Risk Markers and Secondary Outcomes

Secondary endpoints included cardiovascular improvements at 12 mg: systolic blood pressure fell 14.0 mmHg,[1] non-HDL cholesterol and triglycerides decreased,[1] and hsCRP (inflammation marker) dropped.[1]

All key secondaries were met.[1] These changes reduce heart disease risk, common in obese OA patients.

Safety Data and Side Effects from Retatrutide Knee OA Phase 3 GZBJ

Safety in retatrutide knee osteoarthritis trial results phase 3 GZBJ aligned with class effects but showed higher discontinuations.[1] Gastrointestinal issues dominated, with a notable skin sensation side effect.[1]

Common Adverse Events: Nausea, Diarrhea, and GI Issues

Most common were nausea (43.2% at 12 mg, 38.1% at 9 mg) and diarrhea (33.1% and 34.7%).[1] Constipation, vomiting, and decreased appetite also occurred, more than placebo (nausea 10.7%).[1]

These were mostly mild to moderate, peaking during dose escalation. They mirror GLP-1/GIP drug profiles.

Discontinuation Rates and BMI Correlations

Discontinuation due to adverse events hit 18.2% at 12 mg and 12.2% at 9 mg, versus 4-4.8% placebo.[1] Rates were higher in lower BMI groups (e.g., 12.1% vs. more tolerable in BMI ≥35).[1]

Dysesthesia: 20.9% Incidence and Management

Dysesthesia, an unpleasant skin tingling or burning, affected 20.9% at 12 mg (8.8% at 9 mg, 0.7% placebo).[1] It was mostly mild and rarely led to stopping treatment.

Details on dysesthesia side effects in retatrutide trials. This may raise flags for regulators; see dysesthesia impact on retatrutide FDA advisory.

Legal Status, FDA Approval, and Clinical Trial Updates for GZBJ

Retatrutide knee osteoarthritis trial results phase 3 GZBJ are topline only, with no regulatory approval yet.[1][2] The TRIUMPH program advances, but full data awaits.

Current FDA Approval Status of Retatrutide

Retatrutide lacks FDA approval as of early 2026.[2] It remains investigational for obesity and OA. Phase 3 successes build the NDA case, but safety reviews continue.

TRIUMPH Program Context and Pending Full Results

TRIUMPH-4 is one of four basket trials (TRIUMPH-1 to -4)[4] evaluating retatrutide in obesity, OSA, and knee OA. Type I error was controlled across endpoints.[4]

Full GZBJ results are pending presentation. Kenneth Custer, Lilly EVP, called results a "powerful effect on body weight, pain and physical function."[1]

Legal Access and Compounding Considerations

No legal prescription access exists outside trials. Compounding versions are unregulated and risky, lacking safety data. Patients should await approval.

Implications for Knee Osteoarthritis Treatment and Future Trials

Retatrutide knee osteoarthritis trial results phase 3 GZBJ exceeded phase 2 weight loss (24% at 48 weeks)[3] and added pain relief. It positions the drug as a potential dual therapy.

Comparison to Phase 2 Data and Expectations

Phase 2 focused on obesity/T2D/NASH, not OA-specific.[3] GZBJ's 28.7% loss and 76% pain cut beat expectations, per Lilly.[1]

This validates triple agonism for joint health.

Upcoming Readouts: 7 More Phase 3 Trials in 2026

Seven additional phase 3 trials in obesity/T2D wrap in 2026,[1][4] including retatrutide 4mg maintenance dose in future trials. These test lower maintenance dosing for tolerability.

Readouts could accelerate filing.

Potential for Obesity-Related OA Management

Retatrutide could redefine OA care by tackling root causes. Weight loss eases joint load; pain relief boosts activity.

Long-term data needed, but promise is high for millions affected.

Conclusion: What Retatrutide GZBJ Results Mean for Patients

Retatrutide knee osteoarthritis trial results phase 3 GZBJ balance strong efficacy against tolerability hurdles. Patients gained major weight loss, pain freedom, and function boosts.

Balancing Efficacy, Safety, and Accessibility

GI effects and 18% discontinuations challenge use, especially in lower BMI. Yet, benefits for severe obesity-OA cases shine. No new signals emerged.

Next Steps for Approval and Availability

Full results and more trials precede filing. Track retatrutide availability and release date updates. Patients should discuss potential options with their doctors and stay tuned for regulatory breakthroughs.

References

1. Eli Lilly TRIUMPH-4 Topline Results Press Release
   
2. ClinicalTrials.gov - TRIUMPH-4 (NCT05931367)
   
3. NEJM - Triple–Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial
   
4. Eli Lilly Pipeline - Retatrutide Development Program