Retatrutide Phase 3 TRIUMPH Program: Trial Tracker & Readout Schedule

TRIUMPH-4 Update: Obesity + Knee OA Readout

TRIUMPH-4 is the first trial in the TRIUMPH program to report Phase 3 results. The trial enrolled participants with obesity and knee osteoarthritis — a population where weight loss directly addresses the mechanical and inflammatory drivers of joint disease. For broader cross-asset context, see how this slots into the obesity drug approval tracker.

The headline numbers: participants receiving retatrutide achieved a mean 28.7% body weight loss, the highest figure reported in any retatrutide trial to date. This exceeded the 24.2% seen in Phase 2 at 48 weeks, likely due to the longer treatment duration and the specific population studied. The trial included a retatrutide 9 mg arm, which was evaluated for both weight management and osteoarthritis pain relief.

Beyond weight loss, TRIUMPH-4 demonstrated clinically meaningful improvements in osteoarthritis pain, with reductions in pain score measured using the WOMAC index, a validated instrument for assessing osteoarthritis pain and function. The combination of substantial weight reduction and direct pain relief makes this a significant dataset for Lilly’s regulatory strategy. For the broader regulatory view, see the retatrutide status page.

Background on Lilly’s Triple Agonist Retatrutide

Retatrutide, developed by Eli Lilly and Company, represents a major innovation in the field of obesity and metabolic disease research. As a triple hormone receptor agonist, retatrutide uniquely targets the GIP, GLP-1, and glucagon receptors simultaneously — a mechanism that sets it apart from existing therapies like semaglutide (GLP-1 only) and tirzepatide (GLP-1/GIP dual agonist). For a head-to-head breakdown across the class, see retatrutide vs tirzepatide vs CagriSema.

The triple agonist mechanism enables retatrutide to deliver significant weight loss by enhancing satiety, reducing caloric intake, and increasing metabolic rate. In clinical trials, this has translated into unprecedented reductions in body weight, particularly in adults with obesity and related conditions such as knee osteoarthritis. Beyond weight loss, retatrutide’s broad metabolic effects extend to improvements in cardiovascular and renal outcomes — key considerations for participants with established cardiovascular disease or at elevated risk.

Eli Lilly and Company’s development strategy for retatrutide reflects a holistic vision for obesity research, targeting not only excess body weight but also the downstream complications of metabolic dysfunction. Early data also suggest benefits for fatty liver disease, further underscoring retatrutide’s potential as a comprehensive investigational compound. As the TRIUMPH clinical trial program progresses, retatrutide is positioned to redefine standards for delivering significant weight loss and improving long-term metabolic outcomes — you can also compare it head-to-head with the oral candidate in retatrutide vs orforglipron.

TRIUMPH-1: The Pivotal Body Weight Reduction Trial

TRIUMPH-1 is the primary pivotal trial for the obesity indication — the trial that will form the core of Lilly’s NDA submission. It enrolls adults with obesity (BMI ≥30) or overweight (BMI ≥27) with at least one weight-related comorbidity, such as obstructive sleep apnea or chronic low back pain, excluding type 2 diabetes. The companion retatrutide dosage guide covers the titration schedule used across these arms.

This is a randomized, double-blind, placebo-controlled trial with a treatment duration designed to demonstrate sustained weight loss over a clinically meaningful period. Results are expected in 2026 and will provide the definitive efficacy and safety data needed for FDA review. The primary endpoints are percent change in body weight and the proportion of participants achieving ≥5% weight loss — the readout that anchors the retatrutide approval status page.

TRIUMPH-2: Obesity with Type 2 Diabetes

TRIUMPH-2 evaluates retatrutide in people with obesity and type 2 diabetes — a population where the triple agonist mechanism is particularly relevant. The GIP receptor component enhances glucose-dependent insulin secretion, the GLP-1 component provides appetite suppression and additional glycemic control, and the glucagon component increases hepatic glucose output regulation and energy expenditure.

Phase 2 data in the T2D subgroup showed a 1.9% reduction in HbA1c alongside substantial weight loss, indicating dual benefit in metabolic parameters. TRIUMPH-2 results are expected in 2026 and will be critical for a potential diabetes-plus-obesity label.

TRIUMPH-3: Cardiovascular & Renal Outcomes

TRIUMPH-3 is a cardiovascular outcomes trial (CVOT) enrolling participants with obesity and established cardiovascular disease. This trial is designed to demonstrate that retatrutide reduces major adverse cardiovascular events (MACE) — a requirement that has become standard for the obesity drug class following semaglutide’s SELECT trial results. High-sensitivity C-reactive protein is also being measured in TRIUMPH-3 as a biomarker for inflammation and cardiovascular risk reduction.

CVOTs are inherently longer than weight-loss trials due to the need to accumulate sufficient cardiovascular events. Results are not expected until 2027 at the earliest. While TRIUMPH-3 data may not be required for initial FDA approval of the obesity indication, a positive CVOT would significantly broaden retatrutide’s label and commercial positioning — details that ultimately route back into the approval status tracker.

TRIUMPH-6: Weight Maintenance

TRIUMPH-6 addresses a critical question for any obesity drug: what happens when treatment is discontinued or reduced? The trial evaluates weight maintenance strategies, including dose reduction and treatment withdrawal. Specifically, it is assessing the effectiveness of a maintenance dose and the identification of a target dose to sustain weight loss over time, considering both clinical tolerability and long-term management.

Weight regain after discontinuation has been a significant concern across the GLP-1 class. Semaglutide’s STEP 4 trial showed rapid weight regain upon treatment withdrawal. If TRIUMPH-6 demonstrates durable weight maintenance with a reduced dose or after a defined treatment period, it would address one of the biggest clinical and commercial questions facing the obesity drug category — a finding that would also reshape the retatrutide dosage guide recommendations.

Phase 2 Data: What We Already Know

The Phase 2 trial (published in The New England Journal of Medicine, 2023) established retatrutide as the most potent weight-loss compound in clinical development. At the highest dose (12 mg), participants lost 24.2% of body weight at 48 weeks — and the weight-loss curves had not plateaued, suggesting further reductions would occur with longer treatment.

Fatty Liver / MASLD: Emerging TRIUMPH Data

Fatty liver disease, now commonly referred to as metabolic dysfunction-associated steatotic liver disease (MASLD), is a growing concern among individuals with obesity and related metabolic disorders. Characterized by the accumulation of fat in the liver, MASLD is closely linked to insulin resistance, cardiovascular risk, and chronic kidney disease. Until recently, research options for fatty liver disease have been limited, especially when looking for compounds that address both liver fat content and significant weight loss in parallel.

Emerging data from the TRIUMPH clinical trial program highlight retatrutide’s potential to address this unmet need. In addition to delivering significant weight loss, retatrutide has demonstrated meaningful reductions in liver fat content — a key marker of improvement in associated steatotic liver disease. This effect is attributed to retatrutide’s activation of the glucagon receptor, which promotes hepatic fat oxidation, distinguishing it from other GLP-1 or dual agonist therapies.

The implications of these findings are substantial. By improving liver-fat metrics alongside body weight reduction, retatrutide may inform research models that link cardiovascular risk and renal outcomes in metabolic dysfunction. These benefits, observed in clinical trials, suggest that retatrutide could become a focal point of comprehensive weight-loss research datasets, especially in populations with fatty liver disease.

As research continues, the integration of investigational compounds like retatrutide with broader metabolic-health datasets will be essential for refining trial design. The TRIUMPH program’s results reinforce the promise of innovative compounds that address not only weight loss but also the broader spectrum of metabolic-health endpoints relevant to adults with obesity.

Safety Signals: What the Data Show

Retatrutide’s safety profile is consistent with the GLP-1 receptor agonist class, but the dose-dependent discontinuation rates warrant attention. At the 12 mg dose, 18.2% of participants discontinued due to adverse events in Phase 2 — a higher rate than seen with tirzepatide (approximately 5–7% in SURMOUNT trials) or semaglutide (approximately 6–7% in STEP trials).

The most common adverse events were gastrointestinal: nausea, diarrhea, vomiting, and decreased appetite. These events were most frequent during dose escalation and generally decreased in severity and frequency over time. No unexpected safety signals outside the known GLP-1 class effects were identified.

At the 8 mg dose, the discontinuation rate was 12.2% — still higher than approved competitors but accompanied by 22.8% weight loss, which some researchers argue represents a favorable benefit-risk ratio. The Phase 3 TRIUMPH trials use optimized dose-escalation schedules designed to improve GI tolerability, and their results will provide the definitive safety dataset.

For a comprehensive analysis of retatrutide side effects and tolerability data, see our retatrutide side effects guide.

How TRIUMPH Feeds the Approval Timeline

Eli Lilly has indicated plans to submit a New Drug Application (NDA) for retatrutide in 2026. The submission will be anchored by TRIUMPH-1 and TRIUMPH-2 data, with TRIUMPH-4 providing supplementary evidence for a potential knee OA comorbidity indication. The cross-asset comparison here is moving fast — the recently approved oral candidate is covered in Foundayo (orforglipron) FDA approval.

Assuming a standard 10–12-month FDA review cycle, a potential approval decision could come in 2027. Priority Review designation, if granted, could shorten this timeline by several months. This section is here to show how the trial sequence feeds that path, not to replace the direct status answer.

Key milestones to watch: TRIUMPH-1 readout (2026), TRIUMPH-2 readout (2026), NDA submission announcement, and FDA acceptance of the filing. Track all pipeline milestones on our obesity drug approval tracker, and use the retatrutide status page for the current regulatory position.