The Lancet September 29, 2026

Retatrutide in adults with obesity and type 2 diabetes (TRIUMPH-2): a double-blind, parallel-group, randomised, placebo-controlled, phase 3 trial

Virginia Bellido, Carel W le Roux, Elif I Ekinci, et al.

Bottom Line

In the phase 3 TRIUMPH-2 trial, the novel triple-hormone-receptor agonist retatrutide significantly reduced bodyweight by up to 18.8% over 80 weeks in adults with obesity and type 2 diabetes.

Key Findings

1. At week 80, the mean percentage change from baseline in bodyweight was -11.9% (SE 0.6) for retatrutide 4 mg, -16.8% (0.7) for 9 mg, and -18.8% (0.7) for 12 mg, compared to -5.1% (0.7) for placebo.

2. The estimated treatment differences versus placebo for percentage bodyweight change were -6.9% (95% CI -8.7 to -5.1) with 4 mg, -11.8% (-13.7 to -9.8) with 9 mg, and -13.8% (-15.8 to -11.8) with 12 mg (p<0.0001 for all).

3. Gastrointestinal adverse events were the most common, notably diarrhea (27% for 4 mg, 34% for 9 mg, and 34% for 12 mg vs 13% for placebo) and nausea (14%, 21%, and 28% vs 8%, respectively).

4. Hypotension and dysesthesia occurred more frequently with retatrutide than with placebo (hypotension: 1-6% vs <1%; dysesthesia: 4-7% vs 1%).

5. Permanent treatment discontinuation due to adverse events or death was more frequent in the 9 mg (12%) and 12 mg (8%) retatrutide groups compared with the 4 mg (4%) and placebo (5%) groups.

Study Design

Design

RCT

Double-Blind

Sample

1,152

Patients

Duration

80 wk

Median

Setting

8 countries

Population Adults (aged ≥18 years) with a BMI of ≥27 kg/m² and type 2 diabetes (HbA1c 6.5-10.5%) on stable background treatment for at least 90 days, with at least one prior unsuccessful dietary effort to reduce bodyweight.

Intervention Once-weekly subcutaneous injections of retatrutide at doses of 4 mg, 9 mg, or 12 mg.

Comparator Once-weekly subcutaneous injections of matched placebo.

Outcome Percentage change from baseline to week 80 in bodyweight for the retatrutide 9 mg and 12 mg doses versus placebo.

Study Limitations

• The trial was not powered to evaluate long-term cardiovascular safety or hard microvascular endpoints, which require dedicated and extended outcomes trials.

• Higher rates of distinct adverse events like dysesthesia and hypotension, as well as increased discontinuation rates at higher doses (12% in the 9 mg group), could pose challenges for real-world tolerability.

• While 80 weeks is a robust duration for weight loss assessment, durability of glycemic and weight effects post-discontinuation and long-term safety profile beyond this period remain unestablished.

Clinical Significance

The TRIUMPH-2 trial demonstrates that adding glucagon receptor agonism to GIP and GLP-1 receptor agonism (retatrutide) achieves unprecedented weight loss in patients with type 2 diabetes. Historically, patients with type 2 diabetes have experienced less weight loss from incretin therapies than individuals with obesity alone. Reaching nearly 19% body weight reduction in this specific demographic highlights retatrutide as a highly potent next-generation therapy, bridging the gap between pharmacological management and outcomes traditionally seen with bariatric surgery.

Historical Context

The pharmacological management of obesity and type 2 diabetes has been revolutionized by incretin-based therapies, moving from single GLP-1 agonists (e.g., semaglutide) to dual GIP/GLP-1 receptor agonists (e.g., tirzepatide). Retatrutide represents the next pharmacological evolution: a 'triple G' agonist targeting GIP, GLP-1, and glucagon receptors. The glucagon component is hypothesized to increase hepatic lipid metabolism and resting energy expenditure. TRIUMPH-2 builds on phase 2 data to confirm that this mechanistic triad can deliver transformative weight and metabolic outcomes in phase 3 clinical settings.

Guided Discussion

High-yield insights from every perspective

Med Student

Medical Student

Retatrutide is a 'triple G' agonist, targeting GLP-1, GIP, and Glucagon receptors. Given that glucagon classically stimulates hepatic glucose production and raises blood sugar, how does its inclusion in this molecule benefit patients with obesity and type 2 diabetes rather than worsening their glycemic control?

Key Response

While glucagon does increase hepatic glucose output, it also significantly increases energy expenditure, thermogenesis, and satiety. When combined with GLP-1 and GIP agonism, the hyperglycemic effects of glucagon are counteracted by enhanced glucose-dependent insulin secretion, while the synergistic effects on appetite and energy expenditure drive massive weight loss, ultimately improving insulin sensitivity.

Resident

A patient with type 2 diabetes currently managed on metformin, empagliflozin, and glimepiride is starting retatrutide for severe obesity. Given the profound 18.8% weight loss and metabolic effects observed in TRIUMPH-2, what immediate medication adjustments are necessary, and how does this agent's weight loss profile compare to that of existing incretins in a diabetic population?

Key Response

Patients with T2D typically lose less weight on incretin therapies compared to non-diabetics. However, retatrutide's ~19% weight reduction in T2D significantly outpaces semaglutide (~10%) and tirzepatide (~15%). Due to the rapid improvement in glycemic control and reduced food intake, insulin secretagogues like glimepiride (or insulins) must be preemptively reduced or discontinued to prevent severe hypoglycemia.

Fellow

Beyond weight loss, the glucagon agonism in retatrutide has distinct metabolic targets. How does this mechanism specifically alter hepatic lipid metabolism compared to dual GIP/GLP-1 agonists, and what are the clinical implications for a patient with concomitant metabolic dysfunction-associated steatohepatitis (MASH)?

Key Response

Glucagon receptor agonism directly stimulates hepatic lipid oxidation and reduces de novo lipogenesis. This results in a much more rapid and profound clearance of hepatic steatosis compared to GLP-1 or GIP agonism alone, which primarily reduce liver fat indirectly via weight loss. This makes retatrutide a highly promising targeted therapy for resolving MASH and reversing early fibrosis.

Attending

With retatrutide demonstrating near-bariatric levels of weight loss (18.8%) in patients with T2D, we are seeing a shift toward an 'adiposity-first' paradigm for diabetes management. In your clinical practice, how do you address the challenges of long-term therapy adherence, cost-toxicity, and the risk of sarcopenia when committing a patient to this magnitude of pharmacological weight loss?

Key Response

While achieving T2D remission through massive weight loss is now pharmacologically feasible, attendings must navigate significant real-world barriers including insurance step-therapy, high out-of-pocket costs, GI tolerability, and the imperative to prescribe resistance training and high-protein diets to prevent disproportionate lean muscle mass loss during rapid weight reduction.

Scholarly Review

Critical appraisal through the lens of expert reviewers and guideline development

PhD

In trials like TRIUMPH-2, gastrointestinal adverse events often lead to non-random treatment discontinuation. How does the choice between a 'treatment-policy' estimand and an 'efficacy' estimand alter the interpretation of the 18.8% weight loss endpoint, and what imputation methods are most robust for handling this missing data?

Key Response

The treatment-policy estimand evaluates the effect of randomization regardless of adherence, reflecting real-world effectiveness, whereas the efficacy estimand evaluates the effect if the drug is taken as directed. If dropouts due to GI side effects are high, the efficacy estimand may artificially inflate the expected clinical benefit. Robust methods like return-to-baseline multiple imputation are required to avoid bias from missing-not-at-random data.

Journal Editor

As a peer reviewer evaluating the TRIUMPH-2 manuscript, what specific concerns would you raise regarding the cardiovascular safety profile—particularly chronotropic effects—given the inclusion of a glucagon agonist, and what supplemental data would you demand prior to publication?

Key Response

Glucagon agonism is known to increase heart rate and sympathetic tone, which could increase myocardial oxygen demand and arrhythmogenic risk. A rigorous reviewer would flag this and demand detailed analyses of Holter monitor data, incidence of atrial fibrillation, and continuous blood pressure trends to ensure the sympathetic drive does not negate the cardiovascular benefits of massive weight loss.

Guideline Committee

The 2024 ADA Standards of Care strongly recommend highly effective agents (semaglutide, tirzepatide) for weight management in T2D. If approved, does the 18.8% weight loss from retatrutide warrant creating a new 'extremely high efficacy' tier in the ADA/EASD treatment algorithm, and what outcome data is required before it can be recommended over existing therapies for cardiovascular risk reduction?

Key Response

Current guidelines stratify medications by weight loss efficacy (e.g., intermediate, high, very high). Retatrutide's unprecedented efficacy would likely prompt a new algorithm tier for patients requiring >15% weight loss (competing with metabolic surgery). However, to supplant GLP-1 RAs as a Grade A recommendation for ASCVD risk reduction, retatrutide will require completion of dedicated, multi-year cardiovascular outcome trials (CVOTs) proving non-inferiority or superiority in MACE endpoints.

Clinical Landscape

Noteworthy Related Trials

2021

STEP 2 Trial

n = 1210 · Lancet

Tested

Semaglutide 2.4 mg weekly

Population

Adults with overweight or obesity and type 2 diabetes

Comparator

Placebo and Semaglutide 1.0 mg

Endpoint

Percentage change in body weight at week 68

Key result: Semaglutide 2.4 mg led to a 9.6% reduction in body weight versus 3.4% for placebo.

2021

SURPASS-2 Trial

n = 1879 · NEJM

Tested

Tirzepatide 5 mg, 10 mg, or 15 mg weekly

Population

Adults with type 2 diabetes inadequately controlled on metformin

Comparator

Semaglutide 1.0 mg weekly

Endpoint

Change in HbA1c from baseline to week 40

Key result: Tirzepatide was superior to semaglutide in reducing both HbA1c and body weight, with up to 11.2 kg weight loss in the highest dose group.

2023

SURMOUNT-2 Trial

n = 938 · Lancet

Tested

Tirzepatide 10 mg or 15 mg weekly

Population

Adults with obesity or overweight and type 2 diabetes

Comparator

Placebo

Endpoint

Percentage change in body weight at week 72

Key result: Tirzepatide 15 mg resulted in a 14.7% body weight reduction compared to 3.2% with placebo.

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