Retatrutide Phase 3 Results: The Complete TRIUMPH Program Guide 2026

In December 2025, Eli Lilly published the first positive Phase 3 readout for retatrutide (LY3437943), the triple-agonist peptide that had, until then, only been validated at Phase 2 scale. The trial, TRIUMPH-4, reported a mean body-weight reduction of 28.7% at 68 weeks in participants taking the 12 mg weekly dose. That number is not just large in absolute terms, it is the largest weight-loss signal ever reported in a randomized Phase 3 trial of a GLP-1-class compound, and it arrived with additional secondary findings that reframe what "GLP-1 therapy" could eventually mean: a 75.8% reduction in osteoarthritis pain, a roughly 20% drop in LDL cholesterol, and a 72% reversal rate of prediabetes to normoglycemia in the affected subpopulation.

For the research peptide community, this is the moment when retatrutide moves from "promising molecule from a 24-week NEJM paper" to "compound with a Phase 3 dossier under construction". This guide walks through the full TRIUMPH program, the TRIUMPH-4 dataset, the 2026 readouts still to come, how retatrutide stacks up against tirzepatide and semaglutide on published trial data, and what the regulatory picture realistically looks like from here. Retatrutide is still investigational. It is not FDA approved, it is not EMA approved, and all current use remains strictly research-use-only.

What is retatrutide?

Retatrutide, developed by Eli Lilly under the code LY3437943, is a synthetic peptide that simultaneously activates three incretin and metabolic receptors: GLP-1, GIP, and glucagon. It is the first triple agonist to reach Phase 3. Semaglutide (Ozempic, Wegovy) is a GLP-1 mono agonist. Tirzepatide (Mounjaro, Zepbound) is a GLP-1/GIP dual agonist. Retatrutide adds glucagon-receptor agonism on top, which matters for reasons that the TRIUMPH-4 dataset has now made concrete.

The three arms of the mechanism each contribute a distinct effect:

• GLP-1 receptor agonism drives central appetite suppression and slowed gastric emptying. This is the shared mechanism across the entire class and the primary reason all three compounds reduce caloric intake.
• GIP receptor agonism improves insulin sensitivity and modulates adipose tissue. It is what allowed tirzepatide to outperform semaglutide on weight loss in SURPASS and SURMOUNT trials.
• Glucagon receptor agonism increases resting energy expenditure and shifts hepatic lipid metabolism. It is also, per recent mechanistic work, responsible for PCSK9 degradation, which is the likely pathway behind the LDL cholesterol reductions seen in TRIUMPH-4.

The design principle is additive. Each receptor contributes a different lever, and the clinical question Phase 3 needed to answer was whether those levers stack in humans the way they do in preclinical models. As of the TRIUMPH-4 readout, the answer is yes.

Schematic of the triple-receptor mechanism: GLP-1 (teal), GIP (blue) and glucagon (amber).

From Phase 2 to Phase 3: how the story developed

The Phase 2 NEJM study (Jastreboff 2023)

The modern retatrutide story begins with Jastreboff AM et al., published in the New England Journal of Medicine in 2023 (DOI 10.1056/NEJMoa2301972). That trial enrolled 338 adults with obesity or overweight without type 2 diabetes, randomized across placebo and four retatrutide dose levels (1 mg, 4 mg, 8 mg, 12 mg weekly), and followed participants for 24 weeks.

The headline result was a mean 17.5% body-weight reduction at 24 weeks in the 12 mg arm, with clear dose-response behavior across the four active doses. That result immediately placed retatrutide ahead of every other published GLP-1-class compound at comparable follow-up, including tirzepatide in SURMOUNT-1 at the matched timepoint. For a Phase 2 study, it was decisive. It was also the reason Lilly fast-tracked the compound into a large, multi-trial Phase 3 program rather than running additional Phase 2 work.

Why Phase 2 was not enough

A 17.5% weight reduction at 24 weeks in 338 participants is encouraging, but it does not answer the questions regulators ask before an NDA. Those questions are structural:

• Does the weight loss continue, plateau, or rebound past 24 weeks? GLP-1-class compounds generally continue to drive loss out to 60-72 weeks before the curve flattens. A 24-week dataset cannot rule out early peak and late rebound.
• Does the compound work in populations other than obese non-diabetics? Regulators need data in type 2 diabetes, in cardiovascular disease, and in obesity-related comorbidities like osteoarthritis and obstructive sleep apnea.
• Is the safety profile stable at scale? 338 participants is not enough to detect rare but serious adverse events. Phase 3 trials typically enroll thousands.
• Does the cardiovascular-outcomes picture hold? For any compound that will be used for decades in chronic disease, a dedicated MACE (major adverse cardiovascular events) trial is required.

Those questions are exactly the shape of the TRIUMPH program Lilly designed.

The TRIUMPH Program at a glance

TRIUMPH is the umbrella name for Lilly's Phase 3 program for retatrutide. It consists of eight pivotal trials running in parallel, enrolling more than 5,800 participants in total across the weight-management and diabetes indications, plus a separate roughly 10,000-patient cardiovascular outcomes trial. The design and protocol rationale were laid out in detail by Giblin et al. in Diabetes, Obesity and Metabolism in early 2026 (the Wiley DOM TRIUMPH design paper), and the individual trial identifiers are public on ClinicalTrials.gov.

The eight trials, in short:

• TRIUMPH-1 is the pivotal general-obesity trial and the largest in the program. It runs for 80 weeks in adults with obesity or overweight without type 2 diabetes. This is the trial that will carry the weight-management NDA. Readout is expected in Q2-Q3 2026.
• TRIUMPH-2 studies obesity in adults with type 2 diabetes. Readout is also expected in Q2-Q3 2026.
• TRIUMPH-3 studies obesity in adults with established cardiovascular disease, a higher-risk population. 2026 readout.
• TRIUMPH-4 studied obesity plus knee osteoarthritis without type 2 diabetes. Reported positive in December 2025, first Phase 3 readout of the program.
• TRIUMPH-5 is a comparator study in type 2 diabetes, benchmarking retatrutide against an active comparator rather than placebo.
• TRIUMPH-6 studies obstructive sleep apnea with concomitant obesity, a population already targeted by tirzepatide in SURMOUNT-OSA.
• TRIUMPH-CVOT is the cardiovascular outcomes trial, enrolling approximately 10,000 participants with established cardiovascular disease over a 3-4 year timeline, with MACE as the primary endpoint. This is the trial a regulator needs to see before broad cardiovascular labeling.
• A maintenance-dose arm runs alongside the program, evaluating a new 4 mg weekly maintenance dose in addition to the 9 mg and 12 mg arms. The rationale is practical: after titration and after the primary weight loss is achieved, a lower post-titration dose may be enough to hold the result without the GI burden of higher doses.

Taken together, the program is broader than the Phase 3 programs for semaglutide (STEP) or tirzepatide (SURMOUNT, SURPASS). That breadth is deliberate. Lilly is not just building a weight-loss label, it is building a full metabolic-disease label, and TRIUMPH-4 is the first signal that the approach is paying out at Phase 3 scale.

TRIUMPH-4: The first positive Phase 3 readout

Study design

TRIUMPH-4 enrolled 445 adults with obesity or overweight plus knee osteoarthritis, excluding participants with type 2 diabetes. Participants were randomized 1:1:1 to retatrutide 9 mg weekly, retatrutide 12 mg weekly, or placebo, with treatment lasting 68 weeks. The trial was registered as NCT05931367 on ClinicalTrials.gov. Primary endpoints covered percent change in body weight and change in WOMAC pain score; the WOMAC index is the standard validated instrument for osteoarthritis pain and function.

Weight loss results

At 68 weeks, the mean percent change in body weight was:

• Retatrutide 12 mg: -28.7%, equivalent to approximately 32.3 kg (71.2 lb) of absolute loss at baseline averages.
• Retatrutide 9 mg: -26.4%.
• Placebo: -2.1%.

For context, the Phase 2 NEJM result at 24 weeks was 17.5% at the same 12 mg dose. The longer exposure window in TRIUMPH-4 (68 weeks vs 24 weeks) is the main explanation for the larger absolute loss, consistent with what has been seen across the class. The gap between the 9 mg and 12 mg arms is narrow (about 2.3 percentage points) relative to the gap between either active arm and placebo, a pattern that has implications for dose selection in a real-world setting.

Osteoarthritis pain signal

WOMAC pain scores fell by up to 4.5 points, equivalent to a 75.8% relative reduction in pain from baseline. More than 1 in 8 retatrutide-treated participants were completely pain-free at the end of the trial. This is the first Phase 3 GLP-1-class readout that specifically demonstrates symptomatic benefit in knee osteoarthritis beyond what would be expected from weight loss alone, and it opens the possibility, still to be confirmed in dedicated trials, that GLP-1 receptor signaling has direct anti-inflammatory or disease-modifying effects on joint tissue. For now, the clinical interpretation is more conservative: substantial weight loss plus possible direct mechanism produced a large pain benefit in this specific population.

Metabolic secondary findings

Two secondary metabolic signals stood out:

• 72% of participants with prediabetes at baseline reverted to normoglycemia by the end of treatment. This is consistent with the glycemic effects seen across GLP-1-class compounds but at the upper end of what has been reported in non-diabetic cohorts.
• LDL cholesterol dropped by approximately 20%, which is mechanistically unusual for a GLP-1-class compound. The leading explanation, supported by preclinical work, is that glucagon-receptor agonism drives degradation of PCSK9, which in turn increases hepatic LDL-receptor availability and clears circulating LDL. If this signal holds across TRIUMPH-1, TRIUMPH-2, and TRIUMPH-3, retatrutide could end up with a lipid profile that no other compound in the class shares.

Safety and tolerability

The safety profile was, as expected, dominated by gastrointestinal adverse events: nausea, vomiting, and diarrhea. Rates were higher than previously reported for GLP-1 mono agonists (semaglutide) and dual agonists (tirzepatide), which is consistent with a stronger overall incretin load. Dropout was higher in the 12 mg arm than in the 9 mg arm, reinforcing a pattern already visible in Phase 2: the marginal efficacy gain from pushing to 12 mg comes at real tolerability cost. This is the single most important point for dose-selection decisions going forward and is the reason the 9 mg arm and the new 4 mg maintenance dose are under such close scrutiny.

No unexpected safety signals (pancreatitis, thyroid tumor, severe hypoglycemia in the non-diabetic population) were reported above expected background rates in the Lilly summary. Full adverse-event tables will appear in the peer-reviewed publication and in the FDA review package.

Upcoming 2026 readouts

TRIUMPH-1: the pivotal general obesity study

TRIUMPH-1 is the trial that will anchor the weight-management NDA. It runs for 80 weeks (the longest in the program), enrolls a general obesity population without type 2 diabetes, and is designed to be the direct apples-to-apples analogue of SURMOUNT-1 (tirzepatide) and STEP-1 (semaglutide). Readout is expected in Q2-Q3 2026. If TRIUMPH-1 reproduces or exceeds the TRIUMPH-4 efficacy signal in a larger, longer-duration, more general population, it effectively locks in the NDA trajectory.

TRIUMPH-2: obesity with type 2 diabetes

TRIUMPH-2 mirrors TRIUMPH-1 in design but enrolls adults with type 2 diabetes. Historically, GLP-1-class compounds produce somewhat lower percent weight loss in diabetic populations than in non-diabetic ones. TRIUMPH-2 will define whether retatrutide holds a comparable advantage over semaglutide and tirzepatide in that harder-to-treat group. Readout is also expected in Q2-Q3 2026.

TRIUMPH-3: obesity with cardiovascular disease

TRIUMPH-3 studies the higher-risk population of adults with obesity and established cardiovascular disease. Its value is twofold: it tests tolerability in a population with greater comorbidity and polypharmacy, and it provides interim safety data for the cardiovascular label that TRIUMPH-CVOT will eventually anchor.

TRIUMPH-5 and TRIUMPH-6

TRIUMPH-5 is an active-comparator trial in type 2 diabetes, benchmarking retatrutide against an existing GLP-1 rather than placebo. This is where the head-to-head data against tirzepatide or semaglutide may finally surface, at least in the diabetes indication. TRIUMPH-6 focuses on obstructive sleep apnea with concomitant obesity, targeting the same comorbidity where tirzepatide has already secured a label expansion via SURMOUNT-OSA.

TRIUMPH-CVOT

TRIUMPH-CVOT is the cardiovascular outcomes trial and the longest-running part of the program. It enrolls approximately 10,000 participants with established cardiovascular disease, uses MACE as the primary endpoint, and is on a 3-4 year timeline. A positive CVOT readout is what unlocks a broad cardiovascular-risk-reduction claim on the eventual label, analogous to what LEADER did for liraglutide and SELECT did for semaglutide. The CVOT is not expected to report until well after the initial NDA.

The new 4 mg maintenance dose

One practical change in the Phase 3 design is the introduction of a dedicated 4 mg weekly maintenance dose, tested alongside the 9 mg and 12 mg arms. The rationale is clinical rather than statistical. The existing pattern across the GLP-1 class is that the weight-loss curve is driven hardest during titration and the first several months at target dose, and that once the primary loss is achieved, maintenance becomes a separate problem with a different tolerability budget.

For retatrutide specifically, 12 mg weekly produces the largest loss but has the highest GI dropout rate, and 9 mg weekly gives nearly the same loss with better tolerability. A 4 mg maintenance dose, stepped down after the primary weight-loss phase, is aimed at the real-world question of how to hold a 25-28% loss over years without keeping participants on a dose level that many cannot tolerate indefinitely. This echoes the clinical practice already emerging with semaglutide and tirzepatide, where some prescribers step patients down after target weight is achieved.

For research peptide users, the practical implication is that the community conversation about post-titration dosing is about to get a lot more structured. Instead of relying on anecdotal protocols, Phase 3 data will define whether 4 mg weekly is sufficient to hold the result. That is a shift worth tracking. If the 4 mg arm of the TRIUMPH program confirms maintenance efficacy, titration schedules already covered in our retatrutide dosage guide will need an explicit maintenance-phase section beyond the existing 4-12 mg range.

How retatrutide compares to tirzepatide and semaglutide

Direct head-to-head Phase 3 data between retatrutide, tirzepatide, and semaglutide does not exist yet (TRIUMPH-5 is the closest trial currently running in the diabetes population). What does exist is a set of independent Phase 3 trials at matched endpoints, which is the basis for the comparison below. All figures are from peer-reviewed trial publications.

Semaglutide (Wegovy, 2.4 mg weekly), STEP-1, 68 weeks: mean weight loss approximately 14.9%. Mono GLP-1 agonist.

Tirzepatide (Zepbound, 15 mg weekly), SURMOUNT-1, 72 weeks: mean weight loss approximately 22.5%. Dual GLP-1/GIP agonist.

Retatrutide (12 mg weekly), TRIUMPH-4, 68 weeks: mean weight loss 28.7%. Triple GLP-1/GIP/glucagon agonist.

Three observations follow from the numbers. First, the stepwise increase in weight loss as additional receptor mechanisms are added (GLP-1 only to GLP-1+GIP to GLP-1+GIP+glucagon) is consistent with the additive-mechanism hypothesis that underpinned the retatrutide program. Second, the gap between tirzepatide and retatrutide (approximately 6 percentage points) is smaller than the gap between semaglutide and tirzepatide (approximately 7-8 percentage points), which means the incremental benefit of adding glucagon agonism is real but not proportionally larger than the benefit of adding GIP. Third, the TRIUMPH-4 population (obesity plus knee OA) is slightly different from the STEP-1 and SURMOUNT-1 populations (general obesity), so the definitive head-to-head comparison waits for TRIUMPH-1.

On tolerability, retatrutide's GI adverse event rate is higher than tirzepatide's at matched mechanistic dose, which is the tradeoff for the additional mechanism. On metabolic secondary endpoints (LDL, prediabetes reversal, possibly OA pain), retatrutide has signals no other compound in the class has produced. It is too early to say whether those signals translate into a different clinical profile or just a broader label, but they are the reason retatrutide is being followed more closely than any other GLP-1 candidate currently in development.

Regulatory timeline: when could retatrutide actually arrive?

As of April 2026, retatrutide is not approved by the FDA, is not approved by the EMA, and has no active approval in any major regulatory jurisdiction. It is an investigational compound under Phase 3 evaluation. This point matters: retatrutide cannot be legally prescribed, legally sold as a medicine, or legally compounded as a finished drug product at this time.

The plausible timeline, reconstructed from Lilly's disclosed trial schedule and standard regulatory review windows, looks roughly like this:

• Q2-Q3 2026: TRIUMPH-1 and TRIUMPH-2 readouts. These are the two readouts that, combined with TRIUMPH-4, constitute the efficacy core of the eventual NDA.
• Q4 2026 (earliest): NDA filing with the FDA for the weight-management indication. This is the earliest plausible filing window and assumes no regulatory pre-submission issues.
• 2027+: FDA decision. Standard review is approximately 10 months from acceptance; a priority review could shorten this. A 2027 approval is realistic but not guaranteed.
• 6-12 months behind FDA: EMA decision for the EU market, following the standard lag.
• Late 2020s: TRIUMPH-CVOT readout, enabling broader cardiovascular-risk-reduction labeling.

Nothing in this timeline changes the core regulatory status today. There is no approved pharmacy pathway, no approved prescription form, and no approved compounded formulation of retatrutide anywhere in the world. All current use is research-use-only, and the regulatory framing of any material labeled "retatrutide" should reflect that.

What this means for research peptide users in 2026

For the research community, the TRIUMPH-4 readout changes the information landscape more than the regulatory landscape. Retatrutide remains strictly research-use-only. It is not approved, not prescribable, and not marketable as a therapeutic. But the quality of the data supporting any research protocol has moved up substantially, and that has practical implications.

First, titration strategies are now grounded in real Phase 3 dose-response data rather than Phase 2 extrapolation. The 9 mg and 12 mg doses have both been validated at 68-week exposure, with a clear signal that 9 mg offers nearly the same efficacy with better tolerability. Our retatrutide dosage guide has been updated with a new Phase 3 clinical evidence section that incorporates TRIUMPH-4 findings into titration planning.

Second, the practical mechanics of reconstitution, dose calculation, and injection technique are unchanged by the new data, but they matter more now. A compound with a genuine 28.7% weight-loss signal is a compound where dosing errors translate into larger, not smaller, consequences. The step-by-step process in our retatrutide injection guide remains the baseline for careful handling.

Third, sourcing quality becomes the dominant variable. As more trial data accumulates and as the compound attracts more attention, the variance between supplier quality will become more consequential. Research-grade retatrutide should be supplied as lyophilized powder with full certificates of analysis, HPLC-verified purity at or above 99%, and mass spectrometry confirmation of sequence identity. Our research peptides collection lists the general quality criteria that apply across the category.

Fourth, and most importantly: the legal and regulatory framing of all current retatrutide use stays where it has always been. Research-use-only. Not for human consumption outside of a clinical trial. Not a substitute for approved therapy. The Phase 3 data makes the compound more interesting scientifically; it does not make it available clinically.

FAQ

What is retatrutide approved for?

Retatrutide is not approved for any indication, anywhere in the world, as of April 2026. It is an investigational compound under Phase 3 evaluation by Eli Lilly. There is no FDA approval, no EMA approval, and no approved prescription pathway. All current use is strictly research-use-only.

How does retatrutide compare to Mounjaro and Zepbound (tirzepatide)?

Tirzepatide is a dual GLP-1/GIP agonist, already FDA- and EMA-approved for type 2 diabetes (Mounjaro) and obesity (Zepbound). Retatrutide adds a third receptor, glucagon, and has produced larger weight loss in matched-duration trials (28.7% at 68 weeks in TRIUMPH-4 vs approximately 22.5% at 72 weeks in SURMOUNT-1). Retatrutide also shows unique signals on LDL cholesterol and, in TRIUMPH-4, on osteoarthritis pain. The tradeoff is a higher rate of GI adverse events. Direct head-to-head Phase 3 data does not yet exist; TRIUMPH-5 is the closest active-comparator trial.

When will TRIUMPH-1 publish?

Lilly has guided to a Q2-Q3 2026 readout for TRIUMPH-1, the pivotal 80-week general-obesity trial. "Readout" typically means a topline press release first, with full peer-reviewed publication in the following months. A ClinicalTrials.gov results posting usually follows within 12 months of primary-completion date.

Is retatrutide safer than other GLP-1s?

Not based on current data. The TRIUMPH-4 safety profile is qualitatively similar to semaglutide and tirzepatide (GI adverse events dominate) but the rate of nausea, vomiting, and diarrhea is higher than previously seen in the class, and dropout at 12 mg is higher than at 9 mg. No unexpected serious safety signals have been reported so far, but the full safety dataset will take TRIUMPH-1, TRIUMPH-2, TRIUMPH-3, and eventually TRIUMPH-CVOT to characterize.

Where can I legally obtain retatrutide?

Retatrutide is not available by prescription anywhere in the world as of April 2026. Research-grade retatrutide, as a lyophilized reference compound for in vitro and preclinical work, is supplied by specialized research peptide vendors. For any research-use-only protocol, the sourcing criteria are the same as for any research peptide: full certificates of analysis, HPLC purity data, mass spectrometry confirmation, and clearly labeled research-use-only terms. No legal pathway for human use exists outside of an authorized clinical trial.

Key takeaways

• TRIUMPH-4 is the first successful Phase 3 readout for retatrutide, reporting 28.7% mean body-weight reduction at 68 weeks on the 12 mg weekly dose (26.4% on 9 mg, 2.1% on placebo).
• Secondary findings include a 75.8% reduction in WOMAC pain scores in participants with knee osteoarthritis, a 72% prediabetes-to-normoglycemia reversal rate, and an approximately 20% reduction in LDL cholesterol attributed to glucagon-receptor-driven PCSK9 degradation.
• The full TRIUMPH program spans eight Phase 3 trials plus TRIUMPH-CVOT, enrolling more than 5,800 participants in the core weight-management trials and roughly 10,000 in the cardiovascular outcomes trial.
• Retatrutide at 12 mg weekly currently produces the largest weight loss of any published Phase 3 GLP-1-class compound, exceeding tirzepatide (22.5% in SURMOUNT-1) and semaglutide (14.9% in STEP-1) at comparable timepoints.
• A new 4 mg maintenance-dose arm is under evaluation and may define the post-titration strategy once primary weight loss is achieved.
• The tolerability profile is dominated by GI adverse events at higher rates than earlier-generation GLP-1s, with higher dropout at 12 mg than at 9 mg.
• Retatrutide is not FDA approved, not EMA approved, and has no approved prescription pathway as of April 2026. NDA filing is expected in Q4 2026 at the earliest, with an FDA decision realistic in 2027 or later.
• All current use of retatrutide remains strictly research-use-only.