Retatrutide’s first big trial: 28% weight loss in 80 weeks
Eli Lilly’s experimental “triple” hormone medicine helped people lose more than a quarter of their body weight on the top dose.
The study at a glance
- Who took part
- 2,339 adults with obesity, or overweight plus a related health problem, without diabetes
- How long
- 80 weeks of once-weekly injections
- Result
- 19.0%, 25.9% and 28.3% average weight loss on 4, 9 and 12 mg
- Longest follow-up
- 30.3% at 104 weeks on 12 mg, in people with a BMI of 35 or more
- Status
- Company (topline) results; full data still to be published
The research, explained
Retatrutide is an experimental weekly injection that works on three hormone targets at once: GLP-1, GIP and glucagon. Today’s approved weight-loss medicines work on one (semaglutide) or two (tirzepatide).
On May 21, 2026, Lilly announced the first results from TRIUMPH-1, its first large phase 3 trial. After 80 weeks, people on the 12 mg dose had lost 28.3% of their body weight on average, about 70 lb (32 kg). On 9 mg they lost 25.9%, and on 4 mg, 19.0%.
A smaller group with a BMI of 35 or more kept going to 104 weeks. Those on 12 mg had lost 30.3% of their weight by then.
Side effects were mostly stomach-related and rose with the dose. On 12 mg, 42% of people had nausea (15% on placebo) and a quarter had vomiting (5% on placebo). 11.3% stopped the top dose because of side effects, compared with 4.9% on placebo.
Two more phase 3 trials followed in July (read our report). Retatrutide research material is listed in the research shop; it is not Lilly’s investigational medicine.
What does this mean?
If these numbers hold up in the full publication, retatrutide could set a new benchmark for weight-loss medicines.
What don’t we know yet?
These are company-reported topline results, not yet peer-reviewed. Long-term safety, and how much weight comes back after stopping, are still open questions. Retatrutide is not approved anywhere.
Watch and learn
Follow the development of retatrutide alongside background on GLP-1 signalling. Videos may cover a different trial phase; use the source links for the TRIUMPH-1 figures.
Dr Brad Stanfield
Retatrutide: interpreting the newer trial results
A physician reviews retatrutide results. Read the linked trial reports for the population, follow-up and analysis used.
Brad Stanfield, MBChB · general practitioner
Discusses the compound
Discusses Retatrutide, Tirzepatide, Semaglutide or its clinical context. Read the original studies linked here for the exact formulation, population and outcomes.
Dr Brad Stanfield
Retatrutide weight-loss truth
A GP reads the retatrutide trial data and what it does and doesn’t show.
Brad Stanfield, MBChB, general practitioner
Discusses the compound
Discusses Retatrutide, Tirzepatide, Semaglutide or its clinical context. Read the original studies linked here for the exact formulation, population and outcomes.
Ohio State Wexner Medical Center
What is a GLP-1 agonist, and how does it work?
A hospital explainer of GLP-1 signalling, appetite and blood-sugar regulation.
Allison L. Rhodes, MD · obesity medicine
Related biology
Background on GLP-1 signalling for understanding Retatrutide, Tirzepatide, Semaglutide. It does not demonstrate benefits of this compound or formulation.
Sources and references
- TRIUMPH-1: phase 3 retatrutide topline resultsEli Lilly and Company · original sponsor announcement · May 21, 2026
VETUD Learn explains published research in plain language. It is general information, not medical advice. Talk to a doctor before starting, stopping or changing any treatment.
In the research shop
Check the catalog for related laboratory research materials. These products are separate from the approved medicines and clinical trial formulations discussed here.
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