Retatrutide Phase 3 Results: TRIUMPH-1 Trial

Retatrutide is an investigational GIP, GLP-1 and glucagon receptor agonist being studied in the Phase 3 TRIUMPH clinical programme.

In May 2026, Eli Lilly reported topline TRIUMPH-1 results showing substantial body-weight reductions over 80 weeks, with additional 104-week data from a prespecified extension in participants who entered the study with a BMI of 35 or higher.

This article reviews the reported findings, trial design, mechanism and important limitations. It describes the clinical trial formulation studied by Lilly and should not be interpreted as evidence about APS research materials.

What Were the Retatrutide Phase 3 Results?

In TRIUMPH-1, Lilly reported dose-dependent body-weight reductions across the 4 mg, 9 mg and 12 mg groups at 80 weeks.

Under Lilly’s efficacy estimand, participants assigned to 12 mg retatrutide lost an average of 70.3 lb (28.3%) at 80 weeks. Participants assigned to 9 mg lost 64.4 lb (25.9%), while the 4 mg group lost 47.2 lb (19.0%).

In a prespecified blinded extension limited to participants with baseline BMI ≥35, those who continued 12 mg through 104 weeks lost an average of 85.0 lb (30.3%). This 30.3% figure therefore should not be presented as the overall 104-week TRIUMPH-1 result for the full study population.

TRIUMPH-1 Key Findings

Key Finding	Reported Outcome
Primary analysis	80 weeks (efficacy estimand)
4 mg group	−19.0% average body weight
9 mg group	−25.9% average body weight
12 mg group	−28.3% average body weight
Prespecified BMI ≥35 extension (12 mg, 104 weeks)	−30.3% average body weight
Trial stage	Phase 3 (topline results reported by Lilly)

TRIUMPH-1 in One Sentence

TRIUMPH-1 reported average body-weight reductions of 19.0%, 25.9% and 28.3% at 80 weeks across the 4 mg, 9 mg and 12 mg retatrutide groups, respectively, with a prespecified BMI ≥35 extension reporting 30.3% at 104 weeks in the 12 mg group.

The magnitude of the reported reductions has drawn substantial scientific and industry attention, but interpretation should remain tied to the specific population, estimand, trial duration and investigational formulation studied.

Are the TRIUMPH-1 Results Peer Reviewed?

As of September 2026, the headline TRIUMPH-1 efficacy results discussed here were reported publicly by Eli Lilly as topline Phase 3 data. ClinicalTrials.gov lists TRIUMPH-1 as completed, but the registry does not currently display posted study results.

This is different from the 2023 Phase 2 obesity trial, which was published in the New England Journal of Medicine and underwent peer-reviewed publication.

Topline company results can provide important information, but full peer-reviewed publication may add additional detail on statistical methods, subgroup analyses, adverse events and study limitations.

Why Have the TRIUMPH-1 Results Attracted Attention?

The results attracted attention because TRIUMPH-1 is a pivotal Phase 3 obesity study, retatrutide targets three metabolic receptors, and the 12 mg group reported a 28.3% average body-weight reduction at 80 weeks under the efficacy estimand.

Researchers have become increasingly interested in multi-pathway approaches because metabolism is regulated through numerous biological systems rather than a single signaling pathway.

What Is Retatrutide and How Is It Different?

Retatrutide is an investigational unimolecular agonist of the GIP, GLP-1 and glucagon receptors currently being evaluated in multiple Phase 3 trials.

Unlike earlier metabolic peptides that focused on one or two receptor systems, Retatrutide targets:

GLP-1 receptors
GIP receptors
Glucagon receptors

Retatrutide at a Glance

Feature	Retatrutide
Category	Metabolic peptide
Type	Triple agonist
Pathways	GLP-1 + GIP + Glucagon
Research Focus	Appetite, metabolism, energy balance
Development Status	Investigational; multiple Phase 3 trials

The addition of glucagon receptor agonism distinguishes retatrutide mechanistically from dual GIP/GLP-1 agonists such as tirzepatide.

Why Retatrutide’s Triple-Receptor Design Is Being Studied

Retatrutide combines GIP, GLP-1 and glucagon receptor agonism within one molecule, allowing researchers to study coordinated effects across appetite-related, nutrient-sensing and energy-metabolism pathways.

Why Retatrutide Is Being Studied

Research Area	Research Context
Appetite regulation	Hunger and satiety signaling
Metabolic health	Energy balance research
Body composition	Weight and body-composition endpoints
Energy expenditure	Glucagon receptor-related energy-metabolism endpoints
Triple agonism	Three pathways studied simultaneously

These areas describe research questions rather than established therapeutic outcomes.

Inside the TRIUMPH-1 Trial: How Was the Study Conducted?

To understand the significance of the new findings, it is important to look at how the TRIUMPH-1 study was designed.

TRIUMPH-1 is a Phase 3 obesity trial sponsored by Eli Lilly. It enrolled adults with obesity, or overweight with at least one weight-related comorbidity, without diabetes in the main obesity cohort.

The main efficacy analysis was at 80 weeks. ClinicalTrials.gov lists the overall study duration at approximately 89 weeks, with additional prespecified extension follow-up in selected participants.

The trial used protocol-defined titration schedules across assigned maintenance doses. These schedules are clinical-trial procedures and should not be presented as dosing guidance.

TRIUMPH-1 Study Overview

Study Characteristic	Details
Trial	TRIUMPH-1
Sponsor	Eli Lilly
Phase	Phase 3
Population	Adults with obesity, or overweight with a weight-related comorbidity, without diabetes
Primary efficacy assessment	80 weeks
Primary Focus	Weight-related outcomes

Longer follow-up can provide additional information on efficacy persistence and adverse-event patterns, although 80–104 weeks should not be equated with definitive long-term safety.

Three Key TRIUMPH-1 Findings

While the study contains numerous data points, three findings are central to interpreting the topline results.

1. Weight-Related Outcomes

The most widely discussed finding from the TRIUMPH-1 trial was the reported magnitude of weight-related outcomes observed during the study period.

Retatrutide groups showed greater average reductions than placebo.

2. Triple-Pathway Activity

Another major reason the study attracted attention is Retatrutide’s unique mechanism of action.

Unlike traditional GLP-1 compounds, Retatrutide simultaneously activates three receptor pathways:

GLP-1
GIP
Glucagon

Researchers have spent years studying GLP-1 and GIP signaling because of their role in appetite regulation and metabolic communication. Retatrutide adds a third component by activating glucagon receptors, creating what is known as a triple agonist peptide.

The three-receptor profile distinguishes retatrutide mechanistically from single- and dual-receptor incretin therapies.

3. Extended Follow-Up

TRIUMPH-1 extends the evidence base beyond the 48-week Phase 2 obesity trial, with the main Phase 3 analysis at 80 weeks and a prespecified BMI ≥35 extension through 104 weeks.

What Did TRIUMPH-1 Report About Safety and Tolerability?

Lilly reported that the most common adverse events were gastrointestinal and were generally similar to those seen with incretin-based therapies. Discontinuation rates due to adverse events varied by dose and should be interpreted alongside the full Phase 3 dataset when it becomes available in peer-reviewed form.

The trial also collected broader safety and cardiometabolic outcomes, but topline efficacy percentages should not be interpreted independently of tolerability and adverse-event data.

Can TRIUMPH-1 Be Directly Compared With Earlier GLP-1 Trials?

Not reliably from separate trials alone. Retatrutide studies have reported larger numerical body-weight reductions than some earlier GLP-1 or dual-agonist trials, but populations, trial durations, estimands, dose strategies and endpoints differ.

Without a direct randomized head-to-head trial, cross-trial percentages should be treated as descriptive rather than proof that one compound outperforms another.

How Do These Results Compare With Earlier Retatrutide Studies?

The Phase 3 findings build upon earlier research that first drew attention to Retatrutide’s potential.

The 2023 NEJM Phase 2 Study

The 2023 Phase 2 trial, published in the New England Journal of Medicine, enrolled 338 adults and reported a mean 24.2% body-weight reduction at 48 weeks in the 12 mg group versus 2.1% with placebo. These findings helped establish the rationale for Phase 3 investigation.

The newer TRIUMPH-1 results build upon this earlier evidence by extending the observation period and providing additional data from a larger Phase 3 program.

Retatrutide Research Timeline

Study	Duration	Key Observation
Phase 2 (NEJM 2023)	48 weeks	Up to ~24.2% reduction reported
TRIUMPH-1 Phase 3	80 weeks	~28.3% average reduction reported
TRIUMPH-1 prespecified BMI ≥35 extension	104 weeks	30.3% average reduction (12 mg, BMI ≥35 subgroup)

Sources: New England Journal of Medicine (2023); Eli Lilly TRIUMPH-1 Phase 3 Results.

Which Receptors Does Retatrutide Target?

Retatrutide has attracted attention largely because of the biological pathways it targets.

GLP-1 Pathway

GLP-1 is one of the most studied pathways in metabolic research.

Researchers investigate GLP-1 because it plays an important role in appetite signaling, satiety communication, and glucose-related biological processes. Many well-known metabolic compounds target this pathway.

GIP Pathway

GIP is another hormone involved in nutrient sensing and metabolic communication.

Researchers study GIP because it interacts with pathways related to energy balance, nutrient processing, and metabolic regulation. Combining GLP-1 and GIP activity has already been explored successfully in earlier dual-agonist compounds.

Glucagon Pathway

Glucagon receptor agonism is the main mechanistic difference from dual GIP/GLP-1 agonists.

Researchers study glucagon because it is associated with:

Energy expenditure
Liver metabolism
Substrate utilisation and energy-expenditure-related pathways in mechanistic research

The addition of glucagon receptor activity is one reason Retatrutide has generated such significant interest within the scientific community.

Why the Third Pathway Matters

Retatrutide’s triple-agonist design allows researchers to investigate three metabolic pathways simultaneously.

Retatrutide Pathway Profile

Pathway	Retatrutide
GLP-1	✓
GIP	✓
Glucagon	✓

The triple-receptor profile provides a distinct experimental and pharmacological strategy within incretin-based obesity research.

Retatrutide vs Tirzepatide: Why Researchers Are Making Comparisons

Comparisons between Retatrutide and Tirzepatide have increased substantially since the release of the new Phase 3 findings.

Both compounds share GLP-1 and GIP receptor activity, making them closely related from a scientific perspective. However, Retatrutide adds glucagon receptor activity, creating an additional pathway that researchers continue to evaluate.

Retatrutide vs Tirzepatide

Feature	Retatrutide	Tirzepatide
Type	Triple agonist	Dual agonist
GLP-1	✓	✓
GIP	✓	✓
Glucagon	✓	✗
Research Status	Phase 3	Approved for specified indications

The mechanistic difference is glucagon receptor agonism; whether this translates into superior clinical outcomes requires direct comparative evidence.

What Do the New Findings Mean for Obesity Research?

The latest Retatrutide Phase 3 results arrive at a time when obesity and metabolic health remain major global public health challenges.

TRIUMPH-1 provides late-stage clinical evidence that a GIP/GLP-1/glucagon triple-receptor strategy can produce substantial body-weight changes in the studied population. It does not establish that all multi-pathway approaches will produce similar outcomes.

Retatrutide also represents a broader shift in obesity research. Earlier generations of compounds primarily focused on single pathways, while newer investigational peptides are designed to engage multiple signaling systems at once. This evolution reflects a growing understanding that obesity and metabolism involve complex biological networks rather than isolated mechanisms.

As research continues, Retatrutide may help scientists better understand how GLP-1, GIP, and glucagon pathways interact within the broader context of metabolic health.

What Researchers Still Don’t Know

Despite the attention surrounding the TRIUMPH-1 findings, important questions remain unanswered.

While the reported outcomes have generated considerable interest, Retatrutide remains an investigational compound undergoing continued scientific evaluation. Researchers continue to study how findings observed in controlled clinical environments may translate into broader real-world settings.

Several areas remain under active investigation:

Long-term outcomes beyond current study durations
Real-world effectiveness and safety after any future regulatory approval
Differences between patient populations
Long-term safety observations
Additional Phase 3 readouts, peer-reviewed publications and regulatory review
How outcomes compare in direct head-to-head trials with other obesity medicines
Longer-term safety beyond the current observation periods
Additional peer-reviewed publications

It is also important to recognize that scientific understanding evolves over time. Early findings often generate new questions that require further study, replication, and long-term observation.

For this reason, researchers generally view the current Retatrutide data as an important milestone rather than a final conclusion. Ongoing clinical programs and future publications will continue shaping our understanding of this compound and its potential role within metabolic research.

Why Research Quality Matters

The clinical outcomes reported in TRIUMPH-1 apply to the investigational pharmaceutical formulation used in Lilly’s controlled trial. They should not be attributed to separately supplied research materials simply because they share the name retatrutide.

Quality indicators for laboratory research materials include:

Compound identity
Batch-specific COA
Analytical purity method
Identity confirmation
Lot traceability
Stability information

For additional information, see:

View Certificates of Analysis for Research Materials →

For broader mechanistic and evidence context, APS publishes research-focused resources on retatrutide and related metabolic compounds:

APS research materials are supplied strictly for laboratory and scientific research and are not intended for human or veterinary administration. Clinical findings from Lilly’s investigational formulation should not be used to imply equivalent safety, efficacy or pharmacokinetics for APS materials.

Explore Retatrutide Research Guides →

Frequently Asked Questions

What did the Retatrutide Phase 3 trial show?

Lilly reported average body-weight reductions of 19.0%, 25.9% and 28.3% at 80 weeks in the 4 mg, 9 mg and 12 mg groups, respectively, under the efficacy estimand. A prespecified extension in participants with baseline BMI ≥35 who continued 12 mg reported an average 30.3% reduction at 104 weeks.

What are the TRIUMPH-1 findings?

TRIUMPH-1 reported dose-dependent body-weight reductions and additional cardiometabolic and safety observations in adults with obesity or overweight and weight-related comorbidity without diabetes.

How much weight reduction was reported in the Retatrutide Phase 3 study?

Under the efficacy estimand, the 12 mg group lost an average of 28.3% at 80 weeks (25.9% with 9 mg and 19.0% with 4 mg). The 30.3% figure at 104 weeks comes from a prespecified extension subgroup with baseline BMI ≥35, not the full study population.

Why are the TRIUMPH-1 results considered important?

They provide pivotal Phase 3 evidence for a GIP/GLP-1/glucagon triple-receptor agonist and extend the observation period beyond the earlier 48-week Phase 2 trial.

Is Retatrutide a triple agonist peptide?

Yes. Retatrutide is classified as a triple agonist peptide because it activates GLP-1, GIP, and glucagon receptors simultaneously.

What pathways does Retatrutide target?

Retatrutide targets GLP-1, GIP and glucagon receptors. This combination is one of the key features distinguishing it from earlier metabolic compounds.

Why Has Retatrutide Attracted Scientific Attention?

Because it combines triple-receptor agonism with substantial body-weight changes reported in late-stage clinical trials. It remains investigational, and full interpretation requires safety, peer-reviewed and regulatory data.

Did Retatrutide show better results than Tirzepatide?

Separate trials have reported different numerical outcomes, but they are not a direct head-to-head comparison. Differences in populations, duration, estimands and study design prevent a reliable conclusion that one is superior based on cross-trial percentages alone.

Does Retatrutide include glucagon activity?

Yes. Retatrutide includes glucagon receptor activity in addition to GLP-1 and GIP signaling. This additional pathway is a major reason researchers are studying the compound.

What is the latest research on Retatrutide?

As of September 2026, major recent developments include TRIUMPH-1 Phase 3 obesity results and additional Phase 3 readouts across obesity-related conditions and type 2 diabetes. Retatrutide remains investigational.

Are Retatrutide studies still ongoing?

Yes. TRIUMPH-1 is listed as completed, while the broader Retatrutide Phase 3 clinical programme continues across additional populations and indications.

What makes Retatrutide different from other GLP-1 compounds?

Retatrutide activates GIP, GLP-1 and glucagon receptors, whereas single- or dual-receptor incretin therapies have different receptor profiles.

Was TRIUMPH-1 Published in a Peer-Reviewed Journal?

The headline 2026 TRIUMPH-1 results cited here were reported by Eli Lilly as topline Phase 3 data. The earlier Phase 2 obesity trial was published in the New England Journal of Medicine.

Does the 30.3% Figure Apply to Everyone in TRIUMPH-1?

No. The 30.3% average was reported at 104 weeks in a prespecified extension of participants with baseline BMI ≥35 who continued the 12 mg dose. The main 80-week 12 mg result was 28.3%.

Do TRIUMPH-1 Results Apply to Research-Grade Retatrutide Materials?

No. The clinical results apply to Lilly’s investigational formulation used under controlled trial conditions. They should not be attributed to separately supplied research materials.

Sources

Retatrutide Phase 3 Results