Retatrutide in obesity with type 2 diabetes: reading the TRIUMPH-2 phase III report

The Indian Practitioner has reported results from TRIUMPH-2, a phase III trial of retatrutide, an investigational once-weekly injection from Eli Lilly, in adults living with both obesity and type 2 diabetes ^[1]. According to the outlet, which credits part of its account to Medical Xpress, the findings appeared in The Lancet and showed dose-related weight loss and lower glycated haemoglobin over 80 weeks ^[1]. The drug is not approved, and the report notes that further clinical evaluation and regulatory review are still required ^[1].

What the trial tested

Retatrutide is described as a triple agonist, meaning one molecule that activates the receptors for three hormones: glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP) and glucagon ^[1]. Semaglutide, by comparison, acts on the GLP-1 receptor alone, and tirzepatide acts on GLP-1 and GIP receptors ^[1]. The report presents the glucagon component as something that may raise energy expenditure, a proposed mechanism rather than a measured outcome of this trial ^[1].

TRIUMPH-2 was a randomised, double-blind, placebo-controlled study of 1,152 adults assigned to weekly retatrutide at 4 mg, 9 mg or 12 mg, or to placebo ^[1]. Treatment started at 2 mg and was stepped up every four weeks until each participant reached the assigned dose ^[1].

Reported results at 80 weeks

• Mean body-weight reduction was 11.9% with 4 mg, 16.8% with 9 mg and 18.8% with 12 mg, compared with 5.1% with placebo ^[1].
• At 12 mg, the average loss was reported as roughly 20.7 kg (45.5 pounds), framed relative to the placebo group ^[1].
• In the subgroup with a body mass index (BMI) of 35 kg/m² or higher, the 12 mg dose produced a mean reduction of 21.9% ^[1].
• At 12 mg, 75% of participants lost at least 10% of body weight, and nearly one-third lost 25% or more ^[1].
• Glycated haemoglobin (HbA1c), a blood marker reflecting average glucose over roughly two to three months, fell by 1.4–1.5 percentage points across the active groups versus 0.45 points with placebo ^[1].
• Waist circumference, systolic blood pressure and triglycerides also improved, though the report gives no figures for these markers ^[1].

Tolerability

Gastrointestinal effects were the most common adverse events: diarrhoea in up to 34% of participants, nausea in up to 28% and vomiting in up to 16% ^[1]. In the two higher-dose groups, 8–12% of participants discontinued treatment because of adverse events, compared with 5% on placebo ^[1].

Why it matters to these readers

The population studied is the clinically harder one: the report notes that average weight loss with semaglutide and tirzepatide is generally lower in people with type 2 diabetes than in those without it ^[1]. As background, the report also states that losing 5–10% of body weight may improve blood pressure, blood sugar and other cardiovascular risk factors ^[1]. Comparisons with existing drugs should be made cautiously, because, as the article puts it, "results from separate studies should not be interpreted as definitive evidence that one drug is superior to another" ^[1].

What to watch next

The report identifies the open questions as long-term safety, effectiveness across broader patient populations and any effect on obesity-related complications ^[1]. It also points to the need for appropriately designed direct-comparison trials and for regulatory approval before retatrutide could become a routine option ^[1].

Limitations

This take is based on a secondary news report rather than the Lancet paper itself, so all figures are as relayed by The Indian Practitioner ^[1]. The report gives no confidence intervals, p-values or funding details, provides only ranges for some outcomes, and describes the BMI result as a subgroup finding without further detail ^[1].