Eli Lilly's Retatrutide Cuts Body Weight 28.3% in Phase 3 TRIUMPH-1 as Triple-Agonist Data Land at ADA 2026
Eli Lilly presented phase 3 results for retatrutide at ADA 2026 on June 6, showing 28.3% mean weight loss at 80 weeks in obesity and a companion diabetes trial published in The Lancet.
Overview
Eli Lilly presented detailed phase 3 results for retatrutide, an experimental drug that activates three gut and metabolic hormone receptors at once, at the American Diabetes Association’s Scientific Sessions on Saturday, June 6, 2026, at the Ernest N. Morial Convention Center in New Orleans, according to BioSpace. In the pivotal obesity trial TRIUMPH-1, participants on the highest dose lost an average of 70.3 lbs (28.3%) of their body weight at 80 weeks, according to Eli Lilly. A companion trial in type 2 diabetes, TRANSCEND-T2D-1, was simultaneously published in The Lancet, BioSpace reported.
Retatrutide is a once-weekly injectable that targets three receptors at once — GIP, GLP-1, and glucagon — which Lilly describes as a triple agonist, according to Eli Lilly. BioSpace described it as the first triple-hormone therapy for type 2 diabetes and obesity, according to BioSpace. The data position it within a drug class that has reshaped obesity and diabetes care.
What We Know
TRIUMPH-1: obesity results
TRIUMPH-1 randomized 2,339 participants in a 1:1:1:1 ratio to receive retatrutide 4 mg, 9 mg, 12 mg, or placebo, according to Eli Lilly. Participants assigned to the drug “initiated treatment with 2 mg once weekly and increased the dose in a step-wise approach every four weeks.”
At 80 weeks, the primary endpoint, mean body-weight reductions followed a clear dose-response, according to Eli Lilly:
- Retatrutide 4 mg: 47.2 lbs (19.0%)
- Retatrutide 9 mg: 64.4 lbs (25.9%)
- Retatrutide 12 mg: 70.3 lbs (28.3%)
- Placebo: 5.5 lbs (2.2%)
In a pre-specified blinded extension for participants with a BMI of 35 or higher, those who continued on retatrutide 12 mg to 104 weeks lost an average of 85.0 lbs (30.3%), according to Eli Lilly. At 80 weeks, 45.3% of participants achieved at least 30% weight loss — which Lilly called “a level long associated with bariatric surgery” — and 65.3% of those on the 12 mg dose reached a BMI below 30, falling under the threshold for obesity.
“Obesity is a chronic disease, and people living with obesity deserve treatment options that match the complex biology of their neurometabolic disease,” said Ania Jastreboff, M.D., Ph.D., Professor of Medicine & Pediatrics (Endocrinology) at the Yale School of Medicine and the trial’s lead investigator, according to Eli Lilly.
TRANSCEND-T2D-1: diabetes results
The second trial enrolled 537 participants with type 2 diabetes and ran for 40 weeks, according to BioSpace. Participants taking retatrutide achieved average A1C reductions of up to 2.0% from a baseline of 7.9%, and those on the 12 mg dose lost an average of 36.6 lbs (16.8%), according to Eli Lilly. Up to 90% of participants taking retatrutide reached an A1C below 7.0%, and up to 46% reached an A1C below 5.7% — the threshold for normoglycemia.
“As no other trial has reported this magnitude of weight loss, this novel treatment retatrutide has the potential to meaningfully improve the lives of newly diagnosed individuals with type 2 diabetes through life-changing weight and blood glucose management,” said Harpreet Singh Bajaj, MD, MPH, the lead author of TRANSCEND-T2D-1, according to BioSpace.
Effects on obesity-related conditions
Lilly also reported improvements in two complications of obesity. Retatrutide reduced Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) knee-pain subscale scores by up to 4.3 points (73.1%) from a baseline of 6.0, and cut the apnea-hypopnea index — a measure of obstructive sleep apnea severity — by up to 36.1 events per hour (60.6%) from a baseline of 58.6 events per hour, according to Eli Lilly.
“Obesity drives more than 200 downstream diseases, yet we have historically treated those conditions one at a time and in silos,” Jastreboff said, according to Eli Lilly.
Safety
In TRIUMPH-1, the most common adverse events on the 12 mg dose were nausea (42.4% versus 14.8% on placebo), diarrhea (32.0% versus 13.5%), constipation (26.1% versus 10.9%), and vomiting (25.3% versus 4.8%), according to Eli Lilly. Discontinuation due to adverse events rose with dose, reaching 11.3% at 12 mg versus 4.9% on placebo. In the diabetes trial, adverse events were “similar to those of GLP-1 receptor agonists already in use, with no new reported safety concerns,” according to BioSpace.
What We Don’t Know
The TRIUMPH-1 and TRANSCEND-T2D-1 data presented at ADA 2026 are trial results, not a regulatory decision; Lilly did not announce a filing timeline or approval date for retatrutide in either obesity or diabetes in these releases. Head-to-head comparisons against currently marketed drugs were not part of these trials, so any advantage over earlier-generation agents rests on cross-trial figures rather than direct comparison. The longer-term durability and safety of the glucagon-receptor mechanism — the feature that distinguishes retatrutide from existing dual agonists — will depend on data beyond the two-year window reported here.
Analysis
Retatrutide’s TRIUMPH-1 numbers extend a trajectory in which each new agent in the incretin class has pushed average weight loss higher. The 28.3% figure at 80 weeks, and 30.3% in the higher-BMI extension cohort, approach reductions Lilly itself frames as comparable to bariatric surgery, according to Eli Lilly. The simultaneous reporting of benefits in knee osteoarthritis pain and sleep apnea reflects a broader industry shift toward framing obesity drugs as treatments for a cascade of related conditions rather than weight alone. Whether retatrutide’s added glucagon activity translates into a durable clinical edge — and how regulators and payers weigh that against a dose-dependent rise in gastrointestinal side effects and discontinuations — will determine how the drug fits into an increasingly crowded market.