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Retatrutide Phase 2 Trial Design: Arms, Endpoints, and Study Population

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Source-labeled9 min readUpdated Sep 4, 2026
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  1. Main phase 2 randomized obesity trial — design, arms, and primary endpoint
  2. MASLD liver‑fat substudy (phase 2a) — population, endpoint, and results
  3. Body-composition substudy in adults with type 2 diabetes — design and outcomes
  4. Safety and tolerability signals reported in phase 2 programs
  5. Relation to planned phase 3 TRIUMPH program and broader evidence context
  6. Design takeaways for arms, endpoints, and populations
  7. Reported study-design details from cited sources
  8. Limitations and research gaps
  9. Documentation checklist
  10. Related research supplies
  11. More Retatrutide research
  12. Sources and references

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This article summarizes published research and reported study designs. It is not medical advice, dosing guidance, or a personal-use recommendation.

This deep dive summarizes the published phase 2 trial designs, arms, endpoints, and studied populations for retatrutide as reported in the reviewed sources.

Main phase 2 randomized obesity trial — design, arms, and primary endpoint

The principal phase 2, double-blind, randomized, placebo-controlled obesity trial enrolled adults with BMI ≥30 or BMI 27–<30 plus at least one weight-related condition and randomized 338 participants across multi-dose retatrutide arms and placebo; treatment was administered once weekly subcutaneously for a planned 48-week treatment period with the prespecified primary endpoint defined as percent change in body weight from baseline to 24 weeks (primary analysis timepoint) (S4). [S4]

Dose groups in the trial included retatrutide 1 mg, 4 mg (two initial-dose strategies reported), 8 mg (two initial-dose strategies reported), and 12 mg (with specified initial dosing differences across randomization strata), plus placebo; the randomization scheme and starting-dose variations were explicitly part of the study design (S4). [S4]

Key reported efficacy outcomes from that trial (least-squares mean percent change in body weight) include −7.2% at 24 weeks for 1 mg, −12.9% for combined 4-mg groups, −17.3% for combined 8-mg groups, and −17.5% for 12 mg versus −1.6% for placebo; weight-change results at 48 weeks were also reported (S4). [S4]

MASLD liver‑fat substudy (phase 2a) — population, endpoint, and results

A randomized, double-blind, placebo-controlled substudy enrolling participants from the phase 2 obesity study selected people with metabolic dysfunction‑associated steatotic liver disease (MASLD) and baseline liver fat ≥10%; 98 participants were randomized to once-weekly subcutaneous retatrutide (1, 4, 8, or 12 mg) or placebo, with the primary objective specified as mean relative change from baseline in liver fat at 24 weeks (S1). [S1]

At 24 weeks the substudy reported dose-dependent reductions in liver fat: −42.9% (1 mg), −57.0% (4 mg), −81.4% (8 mg), −82.4% (12 mg) versus +0.3% for placebo; proportions achieving normal liver fat (<5%) at 24 weeks were also reported by dose (S1). [S1]

Body-composition substudy in adults with type 2 diabetes — design and outcomes

A prespecified body-composition substudy nested within a phase 2 trial enrolled adults aged 18–75 years with type 2 diabetes (HbA1c 7.0–10.5%), stable bodyweight, and BMI 25–50 kg/m2; participants were randomly assigned across multiple retatrutide doses, dulaglutide 1.5 mg, and placebo, and the prespecified primary substudy endpoint was percent change from baseline to week 36 in total fat mass as measured by DXA (S6). [S6]

The substudy reported dose-related reductions in total fat mass at week 36 (examples: 15.2% reduction with retatrutide 4 mg pooled; 26.1% with retatrutide 8 mg pooled; 23.2% with retatrutide 12 mg) with statistical comparisons versus placebo and versus dulaglutide included in the report (S6). [S6]

Safety and tolerability signals reported in phase 2 programs

Across the main phase 2 obesity trial and the body-composition substudy, the most commonly reported adverse events were gastrointestinal and appeared dose-related; the obesity trial report also noted dose-dependent increases in heart rate that peaked at 24 weeks and declined thereafter (S4, S6). [S4] [S6]

In the body-composition substudy, overall adverse-event frequencies were reported as similar between groups, with counts of serious adverse events provided by arm in the substudy report; gastrointestinal events were the most frequently reported adverse events and no deaths were reported in that substudy (S6). [S6]

Relation to planned phase 3 TRIUMPH program and broader evidence context

Sponsor publications describing the TRIUMPH clinical development program indicate a planned set of four multicenter, randomized, double-blind Phase 3 studies (TRIUMPH-1 through TRIUMPH-4) using once-weekly subcutaneous retatrutide versus placebo with nested protocols for obstructive sleep apnea and knee osteoarthritis, enrolling over 5,800 participants across the program and with weight-management percent change in body weight as the primary weight endpoint (S2). [S2]

Contemporary reviews and systematic summaries contextualize phase 2 results by noting that retatrutide is a triple GLP-1/GIP/glucagon receptor agonist with phase 2 programs showing large, dose-dependent weight-loss effects and associated metabolic improvements, while also highlighting ongoing needs to characterize long-term outcomes, body-composition implications (including lean-mass loss vs. fat-mass loss), and broader safety data in larger and more diverse populations (S3, S8, S5). [S3] [S8] [S5]

Design takeaways for arms, endpoints, and populations

Taken together, published phase 2 reports document randomized, double-blind, placebo‑controlled designs with multiple fixed-dose retatrutide arms and dose-escalation/starting-dose variations; primary endpoints focused on percent change in body weight at 24 weeks (main obesity trial), liver‑fat percent change at 24 weeks for a MASLD substudy, and DXA-measured total fat‑mass percent change at week 36 for the type 2 diabetes substudy, with studied populations including adults with overweight/obesity, a MASLD subgroup with ≥10% liver fat, and adults with type 2 diabetes (S4, S1, S6). [S4] [S1] [S6]

Reported study-design details from cited sources

The following table summarizes protocol details reported in cited studies. These details are provided as literature context only and are not recommendations or instructions.

Source Study Type Model / Subject Amount Reported Route Reported Frequency Duration Notes
[S4] Phase II randomized, double-blind, placebo-controlled trial Adults with BMI ≥30 or BMI 27– 1 mg; 4 mg (initial dose 2 mg or initial dose 4 mg); 8 mg (initial dose 2 mg or initial dose 4 mg); 12 mg (initial dose 2 mg); placebo subcutaneous once weekly 48 weeks (primary analysis at 24 weeks; treatment continued to 48 weeks) Randomized 338 adults; primary endpoint: percent change in body weight from baseline to 24 weeks; multiple dose arms including 1 mg, 4 mg (two starting-dose strategies), 8 mg (two starting-dose strategies), and 12 mg; reported efficacy outcomes at 24 and 48 weeks (S4).
[S1] Randomized, double-blind, placebo-controlled substudy (phase 2a) Participants from the phase 2 obesity study with MASLD and baseline liver fat ≥10% Retatrutide 1 mg, 4 mg, 8 mg, 12 mg; placebo subcutaneous once weekly 48 weeks (primary liver-fat assessment at 24 weeks) n=98 randomized; primary objective: mean relative change from baseline in liver fat at 24 weeks; reported dose-dependent liver-fat reductions and proportions reaching normal liver fat (
[S6] Phase 2 randomized, double-blind, parallel-group, placebo-controlled trial substudy (body composition) Adults aged 18–75 years with type 2 diabetes, HbA1c 7.0–10.5%, BMI 25–50 kg/m2 Retatrutide 0.5 mg; retatrutide 4 mg (2 mg initial dose and 4 mg initial dose pooled groups); retatrutide 8 mg (2 mg initial dose and 4 mg initial dose pooled groups); retatrutide 12 mg; dulaglutide 1.5 mg; placebo subcutaneous once weekly 36 weeks (primary substudy endpoint at week 36) Prespecified body-composition substudy assessing percent change in total fat mass by DXA at week 36; enrollment numbers and pooled-group reporting provided; adverse-event summaries and comparisons vs dulaglutide included (S6).

Limitations and research gaps

  • Phase 2 publications provide robust short‑to‑medium term efficacy and safety data but do not substitute for longer-term, large-scale phase 3 or post-marketing evidence; longer-term outcomes and rare adverse events are not available in these reports.
  • Substudy sample sizes (for example, n=98 in the MASLD substudy) are limited and may constrain precision for some subgroup or secondary endpoints.
  • Demographic representation varied by report (for example, the body-composition substudy included a majority White sample), which may limit generalizability to underrepresented populations.
  • Some design details (for example, long-term maintenance strategies after trial end, or patient-level predictors of response) are not fully addressed in the reviewed phase 2 excerpts.

Documentation checklist

  • Locate and review the primary phase 2 randomized trial publication (NEJM, NCT04881760) for arm structure and primary endpoint (S4).
  • For liver-fat-specific outcomes, consult the MASLD substudy report (Nature Medicine) and confirm inclusion criteria (≥10% liver fat) and 24-week liver-fat endpoint (S1).
  • For body-composition endpoints in people with type 2 diabetes, confirm DXA-based primary substudy endpoint and week-36 timepoint (S6).
  • Compare reported safety/tolerability signals across the main trial and substudy reports (GI events, heart-rate changes, SAE counts) (S4, S6).
  • When interpreting external context, review phase 3 program design and broader systematic/review summaries (TRIUMPH program and reviews) (S2, S3, S8).
  • ClinicalTrials.gov trial registration pages (NCT04881760; NCT04867785)
  • DXA laboratory calibration and quality-assurance documentation
  • Central laboratory sample-handling and processing standard operating procedures
  • Trial randomization and blinding procedure documentation

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More Retatrutide research

Sources and references

  1. [S1] Sanyal AJ, Kaplan LM, Frias JP, Brouwers B, Wu Q, Thomas MK. Triple hormone receptor agonist retatrutide for metabolic dysfunction-associated steatotic liver disease: a randomized phase 2a trial.. Nature medicine. 2024. PMID: 38858523. DOI: 10.1038/s41591-024-03018-2
  2. [S2] Giblin K, Kaplan LM, Somers VK, Le Roux CW, Hunter DJ, Wu Q. Retatrutide for the treatment of obesity, obstructive sleep apnea and knee osteoarthritis: Rationale and design of the TRIUMPH registrational clinical trials.. Diabetes, obesity & metabolism. 2026. PMID: 41090431. DOI: 10.1111/dom.70209
  3. [S3] Katsi V, Koutsopoulos G, Fragoulis C, Dimitriadis K, Tsioufis K. Retatrutide-A Game Changer in Obesity Pharmacotherapy.. Biomolecules. 2025. PMID: 40563436. DOI: 10.3390/biom15060796
  4. [S4] Jastreboff AM, Kaplan LM, Frías JP, Wu Q, Du Y, Gurbuz S. Triple-Hormone-Receptor Agonist Retatrutide for Obesity – A Phase 2 Trial.. The New England journal of medicine. 2023. PMID: 37366315. DOI: 10.1056/NEJMoa2301972
  5. [S5] Locatelli JC, Costa JG, Haynes A, Naylor LH, Fegan PG, Yeap BB. Incretin-Based Weight Loss Pharmacotherapy: Can Resistance Exercise Optimize Changes in Body Composition?. Diabetes care. 2024. PMID: 38687506. DOI: 10.2337/dci23-0100
  6. [S6] Coskun T, Wu Q, Schloot NC, Haupt A, Milicevic Z, Khouli C. Effects of retatrutide on body composition in people with type 2 diabetes: a substudy of a phase 2, double-blind, parallel-group, placebo-controlled, randomised trial.. The lancet. Diabetes & endocrinology. 2025. PMID: 40609566. DOI: 10.1016/S2213-8587(25)00092-0
  7. [S7] Ma J, Hu X, Zhang W, Tao M, Wang M, Lu W. Comparison of the effects of Liraglutide, Tirzepatide, and Retatrutide on diabetic kidney disease in db/db mice.. Endocrine. 2025. PMID: 39212900. DOI: 10.1007/s12020-024-03998-8
  8. [S8] Kokkorakis M, Chakhtoura M, Rhayem C, Al Rifai J, Ghezzawi M, Valenzuela-Vallejo L. Emerging pharmacotherapies for obesity: A systematic review.. Pharmacological reviews. 2025. PMID: 39952695. DOI: 10.1124/pharmrev.123.001045

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