Subtitle: The phase 3 TRIUMPH-1 trial evaluated once-weekly GIP–GLP-1–glucagon triple-receptor agonism in adults with obesity without diabetes.
Estimated reading time: 4 minutes
Key takeaways
- Retatrutide produced mean weight reductions of 17.6–25.0% at 80 weeks, compared with 3.9% with placebo.
- Treatment also significantly improved knee osteoarthritis pain and obstructive sleep apnoea severity in prespecified trial subpopulations.
- Greater efficacy at higher doses was accompanied by more gastrointestinal adverse effects, dose reductions and treatment discontinuation.
Why is retatrutide different?
Retatrutide is a once-weekly injectable agonist targeting three nutrient-stimulated hormone pathways: GIP, GLP-1 and glucagon receptors.
TRIUMPH-1 tested whether this triple-receptor approach could produce substantial weight reduction in adults with obesity while also improving important obesity-related conditions.
The trial is particularly relevant because it looked beyond weight alone, incorporating prespecified populations with knee osteoarthritis and obstructive sleep apnoea.
How was TRIUMPH-1 conducted?
TRIUMPH-1 was a phase 3, multicentre, randomised, double-blind, placebo-controlled trial conducted at 131 sites across 11 countries.
A total of 2,339 adults with obesity without diabetes were randomised to once-weekly subcutaneous:
- Retatrutide 4 mg
- Retatrutide 9 mg
- Retatrutide 12 mg
- Placebo
Treatment continued for 80 weeks.
The study population had substantial obesity: mean baseline BMI was approximately 40 kg/m², and more than three-quarters of participants had a BMI of at least 35 kg/m².
Two prespecified subpopulations included 574 participants with knee osteoarthritis and 243 with obstructive sleep apnoea.
How much weight was lost?
Weight reduction was dose-related and substantially greater with retatrutide than placebo.
| Treatment | Mean body-weight change at 80 weeks |
|---|---|
| Retatrutide 4 mg | −17.6% |
| Retatrutide 9 mg | −23.7% |
| Retatrutide 12 mg | −25.0% |
| Placebo | −3.9% |
With the 12-mg dose, the treatment difference versus placebo was −21.0 percentage points.
A substantial proportion of participants achieved very large reductions in body weight. With retatrutide 12 mg, 36.9% lost at least 30% of baseline body weight and 21.1% lost at least 35%.
Were there benefits beyond weight reduction?
Yes. Two major obesity-related complications also improved.
Knee osteoarthritis
At 80 weeks, the WOMAC pain score decreased by:
- −3.5 points with retatrutide 9 mg
- −3.6 points with retatrutide 12 mg
- −1.9 points with placebo
Both higher doses produced significantly greater pain reduction than placebo.
Obstructive sleep apnoea
The mean reduction in apnoea–hypopnoea index was:
- −34.3 events/hour with retatrutide 9 mg
- −31.7 events/hour with retatrutide 12 mg
- −9.9 events/hour with placebo
These findings indicate that the benefits observed in TRIUMPH-1 extended beyond the magnitude of weight loss itself to clinically important obesity-associated disease.
What happened to cardiometabolic measures?
Retatrutide also improved several cardiometabolic measures, including:
- Waist circumference
- Systolic blood pressure
- Triglycerides
- Non-HDL cholesterol
- Fasting insulin
- High-sensitivity C-reactive protein
Among participants who had prediabetes at baseline, 89.4–93.2% of those receiving retatrutide had returned to normoglycaemia by week 80, compared with 54.2% receiving placebo.
These are encouraging metabolic findings, but the trial was not designed to determine whether retatrutide prevents long-term cardiovascular or renal events.
What were the main safety findings?
The most frequent adverse effects were gastrointestinal, particularly nausea, diarrhoea, constipation and vomiting. They were generally mild or moderate and occurred most often during dose escalation.
Treatment discontinuation because of adverse events increased with dose:
- 4 mg: 4.1%
- 9 mg: 6.5%
- 12 mg: 11.2%
- Placebo: 4.6%
Dysaesthesia, injection-site reactions and hypotension were also reported more frequently with retatrutide.
Pancreatitis and major adverse cardiovascular events were uncommon, but event numbers were too small for firm conclusions. Importantly, TRIUMPH-1 was not powered to establish cardiovascular safety.
What could this mean in practice?
TRIUMPH-1 provides phase 3 evidence that triple-receptor agonism can achieve very substantial weight reduction while also improving two clinically important complications of obesity.
The findings therefore support a broader view of obesity pharmacotherapy: successful treatment may be judged not only by the percentage of body weight lost, but also by improvement in obesity-related disease.
However, higher doses brought greater efficacy alongside more dose reduction and treatment discontinuation. This reinforces the potential importance of balancing treatment intensity against tolerability rather than assuming that the highest tolerated dose will be appropriate for every patient.
Important limitations
The study did not include an active comparator. It therefore cannot determine whether retatrutide is superior to semaglutide, tirzepatide or bariatric surgery.
Only about 2% of participants had a baseline BMI below 30 kg/m², limiting generalisability to people with overweight or less severe obesity.
Longer follow-up is also required to establish cardiovascular and renal outcomes and to better define long-term safety.
Clinical takeaway
TRIUMPH-1 showed that once-weekly retatrutide produced up to 25% mean weight reduction at 80 weeks in adults with obesity without diabetes. Importantly, treatment also improved knee osteoarthritis pain and obstructive sleep apnoea severity, demonstrating benefits beyond weight reduction alone.
The magnitude of efficacy is notable, but future clinical use will need to balance weight and disease-related benefits against dose-dependent tolerability and unresolved long-term cardiovascular safety.
Full reference
Jastreboff AM, Kaplan LM, Davies MJ, Wilding JPH, Ahmad NN, Murray M, Du Y, Makarova N, Giblin K, Schloot NC, Wang Y, for the TRIUMPH-1 Investigators. Retatrutide, a Triple Hormone Receptor Agonist, for Treatment of Obesity. New England Journal of Medicine. Published online 29 September 2026. DOI: 10.1056/NEJMoa2604169.