Retatrutide Phase 3 (TRIUMPH Trials): 2026 Update, Timeline & Expected Results

Overview

Retatrutide (LY3437943) is Eli Lilly's investigational triple agonist targeting the GIP, GLP-1, and glucagon receptors simultaneously — a mechanism that produced the largest weight loss percentages ever seen in an anti-obesity drug trial as of its Phase 2 publication in 2023. With 24.2% mean body weight reduction at the highest dose over 48 weeks, retatrutide generated intense clinical and public interest. The subsequent Phase 3 TRIUMPH program represents the critical validation step before regulatory submission. This article consolidates everything known about the TRIUMPH trials as of early 2026: which trials are running, what populations they target, what timeline is realistic, and what results the research community expects based on Phase 2 data.

Phase 2 Results Recap: The Benchmark for Phase 3

Before examining Phase 3, context from Phase 2 is essential — because Phase 3 TRIUMPH trials were designed based on what Phase 2 revealed. The pivotal Phase 2 obesity trial (PMID 37351564, published in NEJM, June 2023) enrolled 338 participants with obesity or overweight and evaluated retatrutide at four maintenance doses over 48 weeks. Key efficacy findings:

• 12 mg dose: Mean body weight reduction of 24.2% — the highest ever reported for a non-surgical anti-obesity drug at 48 weeks at the time of publication
• 8 mg dose: Mean body weight reduction of approximately 22.8%
• 4 mg dose: Mean body weight reduction of approximately 17.5%
• 1 mg dose: Mean body weight reduction of approximately 8.7%
• A concurrent Type 2 diabetes trial showed 16.9% weight reduction with superior glycemic control vs. dulaglutide, with HbA1c reductions of up to 2.2%
• Liver fat reduction: Up to 81% in participants with metabolic dysfunction-associated steatotic liver disease (MASLD/NAFLD)
• Importantly: The 48-week trial did not show a clear plateau in weight loss at the highest dose, suggesting the final weight loss potential may exceed even the 24.2% figure over longer treatment periods

The TRIUMPH Trial Program: What Phase 3 Is Testing

Eli Lilly named the Phase 3 program TRIUMPH (TRiple-hormone receptor actIon Underlying aMPHetamine-free anti-obesity medication studies). Multiple TRIUMPH trials are running in parallel, each targeting a different patient population or indication. This multi-trial structure mirrors Lilly's approach with tirzepatide's SURMOUNT program and Novo Nordisk's STEP program for semaglutide. Known TRIUMPH trials include:

• TRIUMPH-1 (NCT06008873): Adults with obesity (BMI ≥30) or overweight (BMI ≥27) with at least one weight-related comorbidity, without T2D. The flagship weight loss efficacy trial. Primary endpoint: percentage change in body weight at ~72 weeks.
• TRIUMPH-2: Adults with type 2 diabetes and obesity/overweight. Assessing glycemic control (HbA1c) alongside weight loss. Key for the potential T2D indication approval.
• TRIUMPH-3: Exploring retatrutide in metabolic dysfunction-associated steatohepatitis (MASH/NASH) — liver disease indication — reflecting the extraordinary liver fat reduction seen in Phase 2.
• TRIUMPH cardiovascular outcomes trial (TRIUMPH-CV): A long-duration outcomes trial designed to establish cardiovascular risk reduction, required for full regulatory credibility and potential CV indication. This is the longest-running TRIUMPH trial and will not complete until after initial approval.
• Trials examining retatrutide across diverse populations including different BMI categories, age groups, and potentially pediatric populations (preliminary exploration only).

Expected Weight Loss Percentage in Phase 3

The most searched question about retatrutide Phase 3 is: what weight loss percentage will Phase 3 confirm? Based on Phase 2 data and the structural design of Phase 3, analysts and researchers expect:

• Confirmation of approximately 20-24% weight loss at the top dose (12 mg) in Phase 3 populations. Phase 3 includes broader, more diverse populations than Phase 2, which may slightly moderate the mean vs. Phase 2's relatively homogeneous trial group.
• Phase 3 trials run for 72+ weeks vs. Phase 2's 48 weeks — longer duration could reveal whether the 24.2% figure represents a plateau or whether further loss occurs. The lack of plateau in Phase 2 suggests Phase 3 may document even larger losses at 72 weeks.
• For the Type 2 diabetes TRIUMPH trial: slightly lower weight loss percentages are expected (consistent with T2D populations in other drug trials), but with dramatic HbA1c improvement data.
• Some analysts project that retatrutide could show 25-28% weight loss in TRIUMPH-1 at 72 weeks, but 24% is the conservative projection based on extrapolating the Phase 2 dose-response curve.
• Safety and tolerability in larger, longer populations will be critical — specifically whether GI adverse event rates remain manageable and whether the small heart rate increase (+2-4 bpm seen in Phase 2) persists.

Timeline: When Will Phase 3 Complete and When Can We Expect FDA Approval?

The TRIUMPH trial timelines are critical for anyone tracking retatrutide's path to market. Based on ClinicalTrials.gov registration data and Eli Lilly's public communications:

• Trial initiation: TRIUMPH-1 and related trials began enrolling in late 2023 and throughout 2024.
• Primary completion (data collection complete): Projected for late 2025 to mid-2026 for the core TRIUMPH weight loss trials based on their 72-week primary endpoints.
• Data analysis and NDA/BLA preparation: Typically requires 12-18 months after primary completion.
• Regulatory submission (NDA to FDA): Optimistically possible in late 2026 or 2027.
• FDA review period: Standard review takes 10-12 months; priority review (if granted) takes 6 months. Priority review designation for obesity indications has been granted to previous agents.
• Earliest realistic FDA approval: 2027, with 2028 being a more conservative estimate.
• For comparison: Tirzepatide's SURMOUNT-1 Phase 3 trial enrolled from 2021, primary completion was in 2022, NDA submitted in 2022, and Zepbound (tirzepatide for obesity) was approved in November 2023 — approximately 2 years from primary enrollment to approval.
• Lilly has strong regulatory expertise from tirzepatide's success and is likely to pursue accelerated review pathways where possible.

What Phase 3 Will Tell Us That Phase 2 Could Not

Phase 2 was designed to establish dose-finding and signal detection — not to provide the comprehensive evidence needed for regulatory approval. Phase 3 TRIUMPH trials are designed to answer critical questions that Phase 2's sample sizes and durations could not address:

• Cardiovascular outcomes: The Phase 2 trial showed no major adverse cardiovascular events (MACE), but with only 338 participants and 48 weeks, it was not powered to detect rare cardiovascular events. TRIUMPH cardiovascular outcomes trial will provide this data — similar to how LEADER confirmed cardiovascular benefit for liraglutide and SELECT confirmed it for semaglutide.
• Long-term weight loss sustainability: Phase 2 showed continued weight loss at 48 weeks without clear plateau. Phase 3 at 72+ weeks will establish whether loss continues, plateaus, or shows any rebound.
• Rare adverse events: Pancreatitis, medullary thyroid carcinoma risk, and other rare events require tens of thousands of patient-years to properly characterize. Phase 3's larger enrollment (estimated 1,000+ participants per major trial) begins to provide this data.
• Withdrawal effects: What happens when participants stop retatrutide? Phase 2 did not include a withdrawal phase. Phase 3 may include extension or withdrawal sub-studies similar to SURMOUNT's STEP-4 equivalent.
• Diverse populations: Phase 2 participants were mostly white adults. TRIUMPH includes more diverse populations required by FDA guidance for obesity drug approval.
• Quality of life endpoints: Patient-reported outcomes, physical function, and health-related quality of life measures are more rigorously assessed in Phase 3.

Retatrutide vs. Tirzepatide: Phase 3 Timeline Comparison

The most relevant comparison for understanding retatrutide's Phase 3 trajectory is tirzepatide (Mounjaro/Zepbound), which followed a similar regulatory path as a multi-receptor agonist from Eli Lilly. Comparing the two programs:

• Tirzepatide Phase 2 top dose: 15 mg, ~22.5% weight loss over 72 weeks (in Phase 3 SURMOUNT-1)
• Retatrutide Phase 2 top dose: 12 mg, ~24.2% weight loss over 48 weeks — higher efficacy signal, shorter duration
• Tirzepatide time from Phase 3 initiation to FDA approval (obesity): Approximately 3 years
• Retatrutide is approximately 2-3 years behind tirzepatide in its regulatory timeline
• Key advantage retatrutide may leverage: Lilly already has FDA relationships and manufacturing infrastructure from tirzepatide, potentially streamlining the approval process
• Key challenge: Differentiation — with tirzepatide already approved for obesity, retatrutide must demonstrate meaningful incremental benefit or target a specific sub-population to justify the additional drug development cost and approval process
• For MASH/NASH liver disease: Retatrutide's 81% liver fat reduction is remarkable and could provide a differentiated indication where tirzepatide data is less established

2026 Status Update and What to Watch

As of early 2026, the TRIUMPH program is actively enrolling and generating data. Key developments to monitor throughout 2026 include:

• ClinicalTrials.gov updates to TRIUMPH trial status — particularly primary completion date updates which often precede data release by 12-18 months
• Scientific conference presentations (ADA Scientific Sessions, EASD Congress, ObesityWeek) where Lilly may present interim or exploratory TRIUMPH data before primary completion
• Eli Lilly quarterly earnings calls, which typically include Phase 3 program updates when material to the investment thesis
• Any regulatory interactions with FDA (Special Protocol Assessments, Breakthrough Therapy Designations) that Lilly may announce publicly
• Potential publication of TRIUMPH Phase 3 results in major medical journals (NEJM, Lancet) — likely in 2026-2027 if timelines hold
• Competitor pipeline updates: Amgen's MariTide, Novo Nordisk's CagriSema, and Structure Therapeutics compounds may influence Lilly's urgency with retatrutide

References

1. Triple-Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial (2023) — PubMed
2. Retatrutide, a GIP, GLP-1 and Glucagon Receptor Agonist, for People with Type 2 Diabetes: Phase 2 Trial (2023) — PubMed
3. A Phase 2 Trial of the GIP/GLP-1/Glucagon Receptor Agonist Retatrutide and Liver Fat Reduction in MASLD (2024) — PubMed
4. Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1) (2022) — PubMed