---
title: "TRIUMPH-1 Phase 3 Results: Retatrutide Delivers 28.3% Weight Loss in 2,339-Patient Obesity Trial"
description: "Eli Lilly's pivotal TRIUMPH-1 Phase 3 trial of retatrutide (May 21, 2026) reported 28.3% mean weight loss at 12 mg over 80 weeks, with 45.3% of participants losing 30%+ of body weight. Full results, safety profile, and what it means for the regulatory timeline."
url: https://retatrutide.med/blog/triumph-1-bariatric-level-results
date: 2026-05-22
lastUpdated: 2026-05-25
author: "retatrutide.med Editorial"
category: "news"
tags: ["TRIUMPH-1", "Phase 3", "retatrutide", "weight loss", "Eli Lilly", "pivotal trial", "obesity", "clinical trial results", "NDA timeline", "dysesthesia"]
source: retatrutide.med
sourceType: "blog post"
license: CC-BY-NC-SA-4.0
canonical: https://retatrutide.med/blog/triumph-1-bariatric-level-results
---
## The Headline Number

On May 21, 2026, Eli Lilly announced topline results from **TRIUMPH-1**, the pivotal Phase 3 obesity trial of retatrutide (LY3437943). In 2,339 adults with obesity or overweight and at least one weight-related comorbidity (without type 2 diabetes), retatrutide 12 mg produced a mean weight loss of **-28.3% (-70.3 lbs / -31.9 kg) at 80 weeks** under the efficacy estimand. All three doses tested — 4 mg, 9 mg, and 12 mg — met the primary and key secondary endpoints versus placebo.

This is the third positive Phase 3 readout for retatrutide — following TRIUMPH-4 (-28.7% in obesity with knee osteoarthritis, December 2025) and TRANSCEND-T2D-1 (type 2 diabetes, March 19, 2026, HbA1c -1.7 to -2.0 pp and weight -11.5 to -16.8%) — and the most directly comparable to other approved obesity drugs in the broad obesity-without-diabetes population. By every relevant Phase 3 benchmark, it is the most efficacious weight-loss readout reported by any pharmacological agent in this population.

## Dose-by-Dose Weight Loss at 80 Weeks

| Dose | Efficacy estimand | Treatment-regimen estimand |
|---|---|---|
| Placebo | -2.2% (-5.5 lbs) | -3.9% (-9.7 lbs) |
| Retatrutide 4 mg | -19.0% (-47.2 lbs) | -17.6% (-43.7 lbs) |
| Retatrutide 9 mg | -25.9% (-64.4 lbs) | -23.7% (-58.9 lbs) |
| Retatrutide 12 mg | **-28.3% (-70.3 lbs)** | -25.0% (-62.1 lbs) |

The two estimands differ in how they treat participants who discontinued treatment. The efficacy estimand reflects the drug's effect when actually taken; the treatment-regimen estimand reflects the overall effect including discontinuations. Both are statistically significant versus placebo.

For context, the lowest retatrutide dose (4 mg) produced -19.0% — already better than semaglutide 2.4 mg's -14.9% in STEP 1 and approaching tirzepatide 15 mg's -22.5% in SURMOUNT-1.

## The Bariatric-Surgery-Range Responders

The mean numbers are striking, but the responder analysis is the headline. In the 12 mg arm:

- **62.5% of participants lost ≥25% of body weight**
- **45.3% lost ≥30%**
- **27.2% lost ≥35%**
- **65.3% ended the trial with a BMI below 30** (i.e., no longer obese)

These outcomes overlap meaningfully with sleeve gastrectomy and Roux-en-Y gastric bypass results. The 45.3% achieving ≥30% body weight loss is the highest proportion ever reported for any anti-obesity medication. Among participants with severe obesity at baseline (BMI ≥40), 37.5% still reached BMI <30 — meaningful for a population historically considered surgery-only.

## The 104-Week Extension

TRIUMPH-1 included a 24-week extension phase, taking treatment to 104 weeks in 532 participants with baseline BMI ≥35. Crucially, this is where placebo and lower-dose participants were transitioned to maximum tolerated dose (MTD).

| Arm | Weight loss at 104 wk (efficacy estimand) |
|---|---|
| 4 mg → MTD | -27.9% (-73.3 lbs) |
| 9 mg → MTD | -29.5% (-80.7 lbs) |
| 12 mg | **-30.3% (-85.0 lbs)** |
| Placebo → MTD | -19.2% (-49.9 lbs) |

Two observations matter here. First, the 12 mg arm crossed -30% mean weight loss at 104 weeks — no anti-obesity drug has ever done this in a controlled pivotal trial. Second, participants switched from placebo to retatrutide MTD lost 19.2% in just 24 weeks — confirming that retatrutide produces rapid weight loss even after a long delay in starting treatment, which has implications for clinical decision-making about who to treat and when.

## The Dysesthesia Story Looks Better Here

The most-watched safety signal coming into TRIUMPH-1 was dysesthesia (abnormal skin sensations — tingling, numbness, burning). In TRIUMPH-4, this had been reported in 20.9% of the 12 mg group versus 0.7% on placebo — a new finding that emerged in Phase 3.

TRIUMPH-1 reported substantially lower rates:

| Dose | Dysesthesia incidence |
|---|---|
| Placebo | 0.9% |
| 4 mg | 5.1% |
| 9 mg | 12.3% |
| 12 mg | **12.5%** |

The 12 mg rate of 12.5% in TRIUMPH-1 is roughly 40% lower than the 20.9% seen in TRIUMPH-4 at the same dose. Multiple factors could explain this: TRIUMPH-4 enrolled an older population with more comorbidities (knee OA, more advanced metabolic disease); the underlying frequency of nerve sensitivity may differ across populations; or TRIUMPH-4's primary co-endpoint of pain reduction may have made participants more attuned to sensory symptoms.

The Lilly press release notes that dysesthesia events were generally mild to moderate, the majority resolved during treatment, and most participants continued taking retatrutide. This is the most reassuring framing the data could have produced for the FDA review.

## Gastrointestinal Tolerability

Familiar territory for the incretin class:

| Event | 4 mg | 9 mg | 12 mg | Placebo |
|---|---|---|---|---|
| Nausea | 28.6% | 38.4% | 42.4% | 14.8% |
| Diarrhea | 25.2% | 34.1% | 32.0% | 13.5% |
| Vomiting | 10.6% | 22.8% | 25.3% | 4.8% |
| Constipation | 23.8% | 25.9% | 26.1% | 10.9% |

Rates are broadly similar to TRIUMPH-4 and consistent with the GLP-1/GIP/glucagon mechanism. Discontinuation due to adverse events at 12 mg was 11.3% — meaningfully higher than placebo (4.9%) but notably lower than TRIUMPH-4's 18.2% at the same dose, again pointing to better tolerability in the lower-comorbidity TRIUMPH-1 population.

## Where Retatrutide Sits in the Phase 3 Landscape

With TRIUMPH-1 in hand, the head-to-head efficacy picture in adults with obesity but without diabetes looks like this:

| Trial | Drug / Dose | Duration | Mean weight loss |
|---|---|---|---|
| TRIUMPH-1 | Retatrutide 12 mg | 80 wk | **-28.3%** |
| SURMOUNT-1 | Tirzepatide 15 mg | 72 wk | -22.5% |
| REDEFINE-1 | CagriSema 2.4/2.4 mg | 68 wk | -22.7% |
| ATTAIN-1 | Orforglipron 17.2 mg | 72 wk | -12.4% (TRE) |
| SYNCHRONIZE-1 | Survodutide | 76 wk | -16.6% |
| STEP 1 | Semaglutide 2.4 mg | 68 wk | -14.9% |

Retatrutide is approximately 6 percentage points ahead of the next-best Phase 3 obesity drug in adults without diabetes, and twice the mean weight loss of Foundayo (orforglipron) — which is already FDA-approved and on the market.

## What This Means for the NDA Timeline

Eli Lilly maintained its previously communicated guidance at the Q1 2026 earnings call (April 30, 2026, where it elaborated on the March 19 TRANSCEND-T2D-1 results): NDA submission in late 2026 to Q1 2027. The TRIUMPH-1 readout was the most important remaining data gating point for the obesity indication. With it now in hand, the remaining critical readouts are:

- **TRIUMPH-2** (obesity + type 2 diabetes): Expected Q2-Q3 2026
- **TRIUMPH-3** (obesity + established cardiovascular disease): Expected Q3-Q4 2026

A standard 10-12 month FDA review of an NDA filed in late 2026 / Q1 2027 puts the earliest realistic FDA approval in **late 2027 to early 2028**. Priority Review designation could compress this by ~4 months but has not been confirmed for retatrutide.

## What This Doesn't Yet Tell Us

Several questions remain open even after TRIUMPH-1:

1. **Cardiovascular outcomes**: TRIUMPH-Outcomes (the dedicated CVOT, ~10,000 patients) is a 3-4 year trial. Cardiovascular outcomes labeling will not be available at initial approval.
2. **Weight regain**: TRIUMPH-1 did not include a randomized off-treatment phase. The dynamics of weight regain after stopping retatrutide remain unknown — though prior GLP-1 agonist data (STEP 1 extension, STEP 4) suggest substantial regain is likely without continued treatment.
3. **Body composition**: The 12 mg arm lost an average of 31.9 kg. The proportion of that loss attributable to lean mass versus fat mass is a critical secondary outcome that will be reported in the full publication.
4. **MASH efficacy**: SYNERGY/MACELD trials are separate from TRIUMPH and have their own readout timelines.
5. **Head-to-head data**: Retatrutide has never been compared head-to-head against tirzepatide or semaglutide in a randomized trial. All comparisons remain cross-trial.

## Publication Status

Topline results were released via [Eli Lilly press release](https://investor.lilly.com/news-releases/news-release-details/lillys-triple-agonist-retatrutide-delivered-powerful-weight) on May 21, 2026. Detailed data are expected to be presented at the American Diabetes Association 2026 Scientific Sessions (June 5-8, New Orleans) and/or ObesityWeek 2026, with peer-reviewed publication to follow — likely NEJM, given the precedent set by retatrutide's Phase 2 obesity (NEJM 2023) and tirzepatide's SURMOUNT and SURPASS series.

## The Big Picture

TRIUMPH-1 confirms that retatrutide is on track to become the most efficacious anti-obesity medication ever approved. The 28.3% mean weight loss, the 45.3% of participants achieving ≥30% loss, and the continued progression at 104 weeks all support what Phase 2 data had foreshadowed: triple receptor agonism produces a step-change beyond GLP-1 monotherapy and GIP/GLP-1 dual agonism. The dysesthesia signal looks more manageable than TRIUMPH-4 suggested. The remaining Phase 3 readouts are still important, but the question is no longer whether retatrutide works — it is how the eventual label, pricing, and access will shape its impact on the millions of people currently underserved by approved obesity therapies.

Retatrutide remains investigational. It is not FDA-approved and is available only through authorized clinical trials.