Retatrutide Phase 3 Trial: TRIUMPH-1 Results Explained

Review Lilly’s reported TRIUMPH-1 Phase 3 results for investigational retatrutide, including weight outcomes, trial design, adverse events and limitations.

8/5/20265 min read

Retatrutide Phase 3 Trial: Understanding the TRIUMPH-1 Results

On May 21, 2026, Eli Lilly and Company announced topline results from TRIUMPH-1, a Phase 3 clinical trial investigating retatrutide in adults with obesity or overweight and at least one weight-related health condition who did not have diabetes.

The sponsor-reported findings showed substantial average reductions in body weight across all three retatrutide dose groups. However, retatrutide remains an investigational molecule, and these results should be understood within the design and limitations of the clinical trial.

What is Retatrutide?

Retatrutide, also known by the development code LY3437943, is an investigational molecule designed to activate three hormone-receptor pathways:

  • Glucose-dependent insulinotropic polypeptide, or GIP

  • Glucagon-like peptide-1, or GLP-1

  • Glucagon

Because it acts on three receptors, retatrutide is commonly described as a triple hormone receptor agonist.

Researchers are studying whether simultaneous activity across these pathways may influence appetite regulation, energy balance, glucose metabolism and other cardiometabolic processes.

Retatrutide has not been approved by any regulatory authority. Lilly states that it is legally available for human use only through the company’s authorised clinical trials.

What was TRIUMPH-1?

TRIUMPH-1, registered as NCT05929066, was a Phase 3, randomised, double-blind and placebo-controlled clinical trial.

The study enrolled 2,339 adults with obesity or overweight and at least one weight-related comorbidity. Participants included in the main trial did not have type 2 diabetes.

Participants were randomly assigned in equal proportions to receive:

  • Retatrutide 4 mg

  • Retatrutide 9 mg

  • Retatrutide 12 mg

  • Placebo

The main treatment period lasted 80 weeks. The study also included a prespecified extension for selected participants whose body mass index was at least 35 when they entered the trial.

What did Lilly report?

Lilly reported that all three retatrutide doses met the trial’s primary and key secondary endpoints.

At 80 weeks, the reported average changes in body weight were:

Trial groupAverage body-weight changeRetatrutide 4 mg−19.0%Retatrutide 9 mg−25.9%Retatrutide 12 mg−28.3%Placebo−2.2%

The average starting body weight was approximately 112.7 kilograms, or 248.5 pounds.

Participants assigned to the 12 mg group reportedly lost an average of 31.9 kilograms, or 70.3 pounds, over 80 weeks. Participants assigned to the 9 mg and 4 mg groups lost averages of 29.2 kilograms and 21.4 kilograms, respectively.

How many participants reached larger weight-reduction thresholds?

Lilly also reported the proportion of participants who reached weight reductions of at least 25%, 30% and 35%.

In the 12 mg group:

  • 62.5% reportedly achieved at least 25% body-weight reduction.

  • 45.3% reportedly achieved at least 30% body-weight reduction.

  • 27.2% reportedly achieved at least 35% body-weight reduction.

For comparison, 2.2%, 0.5% and 0.3% of placebo participants reached those respective thresholds.

These percentages describe average and categorical outcomes within a controlled clinical trial. They should not be interpreted as guaranteed outcomes for an individual.

What happened during the 104-week extension?

A prespecified extension included 532 participants who entered the trial with a body mass index of at least 35, completed the initial 80-week period and met the extension’s eligibility criteria.

At 104 weeks, Lilly reported average weight reductions of:

  • 27.9% among participants originally assigned to the 4 mg group and subsequently treated to their maximum tolerated dose

  • 29.5% among participants originally assigned to the 9 mg group

  • 30.3% among participants originally assigned to the 12 mg group

The 30.3% result represented an average reduction of approximately 38.5 kilograms, or 85 pounds.

The extension population was more selective than the full randomised population because it included participants who completed the initial study period, tolerated treatment and satisfied additional criteria. Its results should therefore not automatically be generalised to every person who entered the main trial.

Were other health measurements assessed?

According to Lilly’s announcement, participants receiving retatrutide also showed changes in several assessed cardiometabolic measurements, including:

  • Waist circumference

  • Triglycerides

  • Non-HDL cholesterol

  • Systolic blood pressure

  • High-sensitivity C-reactive protein

For example, the reported average reduction in waist circumference at 80 weeks was 24.1 centimetres in the 12 mg group, compared with 3.6 centimetres in the placebo group.

These findings were reported as secondary outcomes. More detailed analysis is needed to understand their clinical significance, durability and relationship to long-term health outcomes.

What adverse events were reported?

The most frequently reported adverse events were mainly gastrointestinal and were broadly consistent with those observed in studies of other incretin-based therapies.

In the 12 mg group, Lilly reported:

  • Nausea in 42.4% of participants

  • Diarrhoea in 32.0%

  • Constipation in 26.1%

  • Vomiting in 25.3%

Dysesthesia, referring to abnormal or unpleasant skin sensations, was reported in 12.5% of participants in the 12 mg group, compared with 0.9% in the placebo group.

Adverse events led to treatment discontinuation in:

  • 4.1% of the 4 mg group

  • 6.9% of the 9 mg group

  • 11.3% of the 12 mg group

  • 4.9% of the placebo group

The higher discontinuation rate in the 12 mg group illustrates the importance of evaluating tolerability alongside average efficacy results.

Important limitations of the announcement

Several factors should be considered when interpreting these results.

The source was a company announcement

The May 21 publication was a news release issued by Eli Lilly, the trial sponsor and developer of retatrutide. It reported topline findings rather than presenting the complete trial dataset in a peer-reviewed journal.

Sponsor announcements can provide important information, but independent review of the full methodology, statistical analyses and complete safety data remains essential.

Average results do not predict individual outcomes

Clinical-trial averages include participants with different starting weights, medical histories, biological responses and treatment tolerability. Individual outcomes can vary considerably.

The extension involved a selected population

Participants in the 104-week extension had completed the initial study period, tolerated their assigned treatment and met additional eligibility criteria. This selection may affect how broadly the extension findings can be applied.

Long-term evidence is still developing

Longer follow-up is needed to assess durability, weight regain following discontinuation, uncommon adverse events and longer-term cardiovascular, renal and metabolic outcomes.

What happens next?

Retatrutide continues to be studied across a wider Phase 3 development programme. Research programmes are evaluating the molecule in populations with obesity, type 2 diabetes and several related medical conditions.

The TRIUMPH-1 findings contribute to the developing evidence base, but they do not represent regulatory approval or establish that retatrutide is suitable for unsupervised personal use.

Conclusion

The sponsor-reported TRIUMPH-1 results suggest that retatrutide produced substantial average body-weight reductions during an 80-week Phase 3 trial, with additional reductions reported in a selected 104-week extension population.

The findings are scientifically notable because retatrutide activates the GIP, GLP-1 and glucagon receptor pathways simultaneously. However, efficacy results must be considered together with adverse events, treatment discontinuations, study-population selection and the absence of regulatory approval.

Further peer-reviewed publication and ongoing clinical research will be important for establishing retatrutide’s complete benefit-risk profile.

Original sources

Eli Lilly and Company. “Lilly’s triple agonist, retatrutide, delivered powerful weight loss in pivotal Phase 3 obesity trial.” Published May 21, 2026.

ClinicalTrials.gov. “A Study of Retatrutide (LY3437943) in Participants Who Have Obesity or Overweight.” TRIUMPH-1, NCT05929066.

Research and educational disclaimer

This article is provided solely as a neutral summary of publicly reported scientific research. It does not constitute medical advice, a treatment recommendation, prescribing information or instructions for personal use.

Retatrutide is an investigational molecule that has not been approved by any regulatory authority. Eli Lilly states that retatrutide is legally available for human use only through its authorised clinical trials. Products described as research materials must not be represented as equivalent to Lilly’s investigational clinical-trial material.