Reta weight loss has attracted attention following clinical trials reporting substantial reductions in body weight. Commonly called “reta”, retatrutide is an investigational drug that acts on three hormone receptors involved in metabolic regulation.

However, the reported results vary between studies. Trial populations, study durations and statistical methods all influence the figures.

On 29 September 2026, researchers published two major Phase 3 trials, TRIUMPH-1 and TRIUMPH-2, in peer-reviewed medical journals. Together, these studies expanded the evidence for retatrutide weight loss in adults with obesity, including people with type 2 diabetes.

This Research Note examines the published findings, explains why different weight-loss percentages appear online and identifies what the evidence does not establish.

What Is Reta Weight Loss?

Reta is a shortened name commonly used for retatrutide, an investigational triple-receptor agonist developed by Eli Lilly.

Retatrutide activates three hormone receptors:

• Glucagon-like peptide-1 (GLP-1)
• Glucose-dependent insulinotropic polypeptide (GIP)
• Glucagon

These pathways influence appetite, glucose regulation and energy metabolism. Researchers are investigating how activating all three receptors affects body weight and related metabolic outcomes.

The term “reta weight loss” generally refers to weight changes observed in retatrutide clinical trials. It does not describe a separate drug.

For a broader explanation of the mechanism, see our analysis of ⁠what retatrutide does.

How Much Weight Loss Did Retatrutide Clinical Trials Report?

Three major published studies provide useful evidence about retatrutide-associated weight reduction.

The original Phase 2 obesity trial reported substantial weight loss over 48 weeks. Two Phase 3 trials subsequently evaluated outcomes over 80 weeks in larger populations.

These figures represent average changes from baseline, not placebo-adjusted treatment effects.

The Phase 2 result uses an efficacy analysis, while the Phase 3 results use treatment-regimen estimands. Differences in populations, durations and statistical methods mean the percentages are not directly equivalent.

The 2023 ⁠Phase 2 obesity trial established the earlier evidence. The September 2026 Phase 3 publications subsequently expanded the findings across larger and clinically important populations.

What Did the Phase 3 Retatrutide Weight Loss Trials Find?

The September 2026 publications provide detailed evidence from two large, randomised, placebo-controlled trials.

Although both investigated retatrutide, they studied different populations.

TRIUMPH-1: Weight Loss in Adults Without Diabetes

TRIUMPH-1 enrolled 2,339 adults with obesity without diabetes.

Researchers assigned participants to retatrutide or placebo groups for 80 weeks. The study evaluated body-weight changes alongside outcomes involving knee osteoarthritis pain and obstructive sleep apnoea.

The New England Journal of Medicine published the results on 29 September 2026.

Using the treatment-regimen estimand, researchers reported these average body-weight changes:

The 12 mg group experienced an average weight reduction of 25.0%, compared with 3.9% in the placebo group.

The estimated difference between the groups was 21.0 percentage points.

Researchers also observed improvements in knee osteoarthritis pain and obstructive sleep apnoea outcomes within the relevant participant subgroups. These findings concern specific clinical endpoints and do not establish benefits for every individual.

The complete findings appear in the ⁠TRIUMPH-1 Phase 3 publication.  

TRIUMPH-2: Weight Loss in Adults With Type 2 Diabetes

TRIUMPH-2 investigated retatrutide in adults with overweight or obesity and type 2 diabetes.

The trial enrolled 1,152 participants across 92 research centres in eight countries. Researchers evaluated weight reduction over 80 weeks.

The Lancet published the findings online on 29 September 2026.

Using the treatment-regimen estimand, researchers reported:

At the highest studied dose, the average reduction was 18.8%, compared with 5.1% for placebo.

The estimated difference between these groups was 13.8 percentage points.

The study also reported improvements in glycaemic control, including reductions in HbA1c, a measure of average blood glucose.

These findings matter because weight-loss responses can differ between populations with and without type 2 diabetes.

However, TRIUMPH-1 and TRIUMPH-2 were separate trials. Their results should not be interpreted as a direct comparison between otherwise identical groups.

The complete findings appear in the ⁠TRIUMPH-2 Phase 3 publication.  

Why Do Some Sources Report 28.3% Weight Loss Instead of 25%?

One important distinction in retatrutide research is how investigators calculate weight-loss outcomes.

In May 2026, Eli Lilly reported an average 28.3% weight reduction in the TRIUMPH-1 12 mg group.

The September 2026 peer-reviewed publication reported 25.0% for the same study group using a different analysis.

Both figures relate to TRIUMPH-1, but they answer different statistical questions.

Researchers use approaches called estimands to define the treatment effect they want to measure.

Treatment-regimen estimand: Estimates the average effect of treatment assignment while accounting for events such as treatment discontinuation, according to the trial’s statistical methods.

Efficacy estimand: Estimates the effect under a hypothetical scenario without specified treatment-disrupting events, such as discontinuation or prohibited additional treatment.

For TRIUMPH-1 at 80 weeks:

The 28.3% figure is not incorrect. It represents a different analysis of the trial data.

However, presenting it without identifying the estimand can give readers an incomplete picture.

Lilly’s ⁠May 2026 TRIUMPH-1 announcement reported the 28.3% figure before publication of the complete peer-reviewed results.  

The same distinction applies to TRIUMPH-2. Its treatment-regimen estimate was 18.8%, while the efficacy estimate was 20.8% in the 12 mg group.

Therefore, comparing retatrutide weight-loss percentages requires more than identifying the largest number. Readers also need to understand how researchers calculated each result.

How Did Weight Loss Progress During the Clinical Trials?

The published trials show that average weight reduction developed over extended study periods.

In the 2023 Phase 2 obesity trial, the 12 mg group experienced an average weight reduction of 17.5% at 24 weeks.

By 48 weeks, the reported reduction reached 24.2%.

The Phase 3 TRIUMPH-1 and TRIUMPH-2 studies evaluated weight outcomes over 80 weeks.

These findings demonstrate why the timing of an assessment matters.

A 24-week result cannot be directly compared with an 80-week result as though researchers measured the same period.

Similarly, group averages do not establish a predictable weight-loss timeline for any individual.

The published findings also do not establish how long weight reduction would persist after treatment ends.

What Did the Trials Show About Side Effects?

Weight reduction was not the only outcome researchers evaluated.

Across the published trials, gastrointestinal adverse events were among the most frequently reported side effects.

These included nausea, diarrhoea, vomiting and constipation.

TRIUMPH-2 also reported hypotension and dysesthesia more frequently in retatrutide groups than in the placebo group.

Some participants discontinued treatment because of adverse events. Discontinuation rates differed between study groups.

These findings matter because the magnitude of weight reduction is only one part of evaluating an investigational drug.

For a detailed examination of adverse events and tolerability, see our analysis of ⁠retatrutide side effects.

What Do the Weight Loss Results Actually Establish?

By October 2026, the published evidence included Phase 2 and Phase 3 trials reporting substantial average weight reductions.

The September 2026 publications strengthened the evidence in several ways.

First, TRIUMPH-1 provided results from a larger trial involving adults with obesity without diabetes.

Second, TRIUMPH-2 expanded the peer-reviewed evidence in adults with overweight or obesity and type 2 diabetes.

Third, the complete publications allowed readers to examine the findings using clearly identified statistical analyses.

Subsequent Phase 3 findings also provide a direct comparison with semaglutide. Our retatrutide vs Ozempic analysis examines the reported weight-loss differences in the 80-week TRANSCEND-T2D-2 trial.

However, important limitations remain.

Trial results are population-specific. Participants met defined eligibility criteria. Consequently, the findings cannot automatically apply to everyone.

The studies cover defined periods. Their results do not establish every longer-term outcome or risk.

Average weight loss does not predict individual results. Participants may respond differently, and group averages cannot establish an individual’s outcome.

Clinical-trial products differ from unverified online products. Published trial findings do not establish the identity, composition, quality or safety of products marketed as “reta” or “retatrutide”.

These distinctions are important when considering ⁠whether retatrutide is safe outside controlled clinical research.

Is Retatrutide Approved for Weight Loss in Australia?

As of October 2026, retatrutide was an investigational drug and had not received approval from Australia’s Therapeutic Goods Administration (TGA).

Positive Phase 3 results do not themselves constitute regulatory approval.

Likewise, the availability of products marketed as retatrutide does not establish that they contain the investigational drug evaluated in clinical trials.

In September 2026, the TGA reported that ⁠testing of one product sold as retatrutide found no retatrutide. Instead, testing identified undeclared semaglutide. This finding concerned the tested product and does not establish the composition of every product marketed under the same name.  

Our separate analysis explains whether retatrutide is ⁠available in Australia and how Australian regulatory status differs from online product availability.

For more information about Retatrutide Australia, including our research supply platform and supporting documentation, visit R10 Research.

Key Takeaways

• Reta refers to retatrutide. The shortened name commonly appears in searches and informal discussions about weight loss.
• Published trials reported substantial average weight reductions. The 2023 Phase 2 study reported 24.2% at 48 weeks in its 12 mg group.
• September 2026 Phase 3 publications expanded the evidence. TRIUMPH-1 reported 25.0% mean weight reduction at 80 weeks in its 12 mg group. TRIUMPH-2 reported 18.8% in adults with type 2 diabetes.
• Different percentages can reflect different analyses. The frequently reported 28.3% TRIUMPH-1 figure comes from an efficacy estimand rather than the treatment-regimen estimate.
• Weight-loss findings do not establish regulatory approval or long-term safety. Retatrutide was investigational in Australia as of October 2026.

Frequently Asked Questions

Is Reta the Same as Retatrutide?

Yes. “Reta” is a commonly used abbreviation for retatrutide, the investigational triple-receptor agonist developed by Eli Lilly.

However, a product labelled “reta” does not automatically contain authentic retatrutide.

For more information about the terminology, see ⁠what is reta peptide and how the term relates to retatrutide research.

How Much Weight Loss Has Retatrutide Shown in Clinical Trials?

In TRIUMPH-1, participants in the 12 mg group experienced an average 25.0% reduction in body weight at 80 weeks using the treatment-regimen estimand.

TRIUMPH-2 reported an average 18.8% reduction in its 12 mg group among adults with overweight or obesity and type 2 diabetes.

These figures describe trial averages rather than predictions of individual outcomes.

Why Do Some Retatrutide Weight Loss Results Say 28.3%?

The 28.3% figure comes from the TRIUMPH-1 efficacy estimand. The treatment-regimen analysis reported 25.0% for the same study group.

The two approaches use different assumptions about treatment-related events and missing data.

Is Reta Approved for Weight Loss in Australia?

As of October 2026, retatrutide had not received TGA approval for weight loss or another therapeutic indication in Australia.

Positive clinical-trial findings do not automatically establish regulatory approval.

Research Sources

Jastreboff AM, et al. ⁠Triple–Hormone-Receptor Agonist Retatrutide for Obesity: A Phase 2 Trial. New England Journal of Medicine. 2023. DOI: 10.1056/NEJMoa2301972.

Jastreboff AM, et al. ⁠Retatrutide, a Triple Hormone Receptor Agonist, for Treatment of Obesity. New England Journal of Medicine. Published online 29 September 2026. DOI: 10.1056/NEJMoa2604169.

Bellido V, et al. ⁠Retatrutide in adults with obesity and type 2 diabetes (TRIUMPH-2): a double-blind, parallel-group, randomised, placebo-controlled, phase 3 trial. The Lancet. Published online 29 September 2026. DOI: 10.1016/S0140-6736(26)01861-1.

Eli Lilly and Company. ⁠Retatrutide Delivered Powerful Weight Loss in Pivotal Phase 3 Obesity Trial. Published 21 May 2026.

Therapeutic Goods Administration. ⁠TGA Tests Counterfeit Retatrutide Product Following Serious Adverse Event Report. Published 14 September 2026.