Study-by-study review

Retatrutide clinical evidence

The strongest published findings, the newest Phase 3 announcements and the limitations visitors should understand before repeating a headline.

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338Participants in the pivotal peer-reviewed Phase 2 obesity trial.

537Randomized participants in peer-reviewed Phase 3 TRANSCEND-T2D-1.

5Positive Phase 3 trials disclosed by Lilly by July 2026.

0Completed public head-to-head trials proving superiority to tirzepatide as of this review.

How to read the numbers: An “efficacy estimand” estimates what might happen if assigned participants stayed on treatment without prohibited rescue treatment. A “treatment-regimen estimand” includes outcomes regardless of adherence or discontinuation and is usually closer to a real-world treatment-policy question. Headlines commonly quote the larger efficacy estimate.

Peer-reviewed research

Published human trial results

These studies underwent journal peer review. Peer review raises confidence; it does not erase sponsor influence, design limitations or unanswered long-term questions.

2023

Peer reviewed

Phase 2 obesity trial — New England Journal of Medicine

Design: 338 adults with obesity, or overweight plus a weight-related condition, without diabetes; randomized to weekly retatrutide or placebo for 48 weeks.

Result: Mean weight change at week 48 was −24.2% with 12 mg, −22.8% with 8 mg, −17.1% with 4 mg and −8.7% with 1 mg, compared with −2.1% for placebo. In the 12 mg group, 83% lost at least 15% of baseline weight.

Limit: Forty-eight weeks cannot establish multi-year safety or durability. Gastrointestinal events were dose-related, and heart rate increased in a dose-dependent pattern before declining after week 24.

Open source #1 →

2023

Peer reviewed

Phase 2 type 2 diabetes trial — The Lancet

Design: 281 adults with type 2 diabetes; placebo, dulaglutide 1.5 mg or several retatrutide regimens; primary A1C endpoint at 24 weeks and weight follow-up at 36 weeks.

Result: The 12 mg group had a −2.02 percentage-point mean A1C change at 24 weeks and −16.94% mean body-weight change at 36 weeks. The 8 mg and 12 mg A1C reductions exceeded dulaglutide 1.5 mg in specified comparisons.

Limit: This was a dose-finding Phase 2 trial, not a comparison with current higher-potency incretin options. Mild-to-moderate gastrointestinal events were the most frequent adverse effects.

Open source #2 →

2024

Peer reviewed

MASLD liver-fat substudy — Nature Medicine

Design: A 98-person substudy of the Phase 2 obesity trial among participants with at least 10% liver fat.

Result: At 24 weeks, mean relative liver-fat change was −82.4% with 12 mg and −81.4% with 8 mg, versus +0.3% with placebo. Liver fat below 5% was reached by 86% of the 12 mg group and 79% of the 8 mg group.

Limit: This was a small, imaging-based substudy. It does not by itself prove improved fibrosis, fewer liver complications or long-term liver outcomes.

Open source #3 →

2025

Peer reviewed

Body-composition substudy — The Lancet Diabetes & Endocrinology

Design: 189 participants enrolled; 103 completed treatment with baseline and week-36 DXA scans.

Result: Total fat mass fell 23.2% with 12 mg and 26.1% with pooled 8 mg. Investigators reported that the proportion of lean-mass loss relative to total weight loss was similar to other obesity treatments.

Limit: The substudy was modest in size and had substantial missing paired scans. “Similar proportion” does not mean no lean-mass loss; nutrition and resistance exercise remain clinically relevant during major weight reduction.

Open source #4 →

2026

Peer reviewed

Phase 3 diabetes trial — TRANSCEND-T2D-1 in The Lancet

Design: 537 adults with early type 2 diabetes inadequately controlled by diet and exercise; retatrutide 4, 9 or 12 mg versus placebo for 40 weeks.

Result: At 12 mg, mean A1C changed −1.94 percentage points and body weight changed −15.3%; placebo changes were −0.81 points and −2.6%. No severe hypoglycemia was reported.

Limit: Participants were not taking background glucose-lowering medicine, average diabetes duration was 2.5 years, and follow-up was 40 weeks. Findings may not transfer directly to longer-standing or more complex diabetes.

Open source #5 →

Phase 3 topline announcements

Important data awaiting full peer-reviewed reports

Topline releases can accurately report major endpoints, but they provide less detail than a full paper and come directly from the sponsor.

Company topline

TRIUMPH-1: obesity without diabetes

At 80 weeks, the efficacy estimate for mean weight change was −28.3% with 12 mg and −2.2% with placebo. The treatment-regimen estimate was −25.0% and −3.9%, respectively. Adverse-event discontinuation at 12 mg was 11.3% versus 4.9% with placebo.

Company topline

TRIUMPH-2: obesity plus type 2 diabetes

At 80 weeks, the reported efficacy estimate reached −20.8% weight change with 12 mg versus −4.0% with placebo, with A1C reductions up to 1.6 percentage points. Full peer-reviewed results were still pending at this review.

Company topline

TRIUMPH-3: severe obesity and cardiovascular disease

At 80 weeks, the reported efficacy estimate reached −22.6% with 12 mg versus −3.2% with placebo. Cardiovascular events were fewer than expected, leaving wide confidence intervals that did not establish cardiovascular benefit or harm.

Company topline

TRIUMPH-4: obesity and knee osteoarthritis pain

The sponsor reported substantial weight reduction and improvement in knee-pain scores over 68 weeks. The study generated unusually large efficacy estimates in some analyses, but a full journal report is needed to evaluate missing data, discontinuation and pain outcomes in detail.

Company topline

Sleep-apnea and related cohorts

TRIUMPH program announcements reported improvements in moderate-to-severe obstructive sleep apnea and other obesity complications. These findings are promising but should be evaluated in the full reports, including baseline severity and adherence to PAP therapy.

Ongoing trial

TRIUMPH-5: retatrutide vs tirzepatide

This active head-to-head study is designed to answer the comparison that cross-trial headlines cannot. Until results are available, statements that retatrutide “beats” tirzepatide remain unproven.

Open source #6 →

What the total evidence supports

Retatrutide produces large average weight reductions in controlled trials, with larger effects generally seen at higher doses and longer treatment durations.
It improves glucose control in type 2 diabetes and has shown substantial reductions in liver fat in a small MASLD substudy.
Gastrointestinal side effects are common, and dysesthesia has emerged as an additional dose-related tolerability issue in Phase 3 reports.
The benefit-risk balance may differ by population. People with diabetes generally lost less weight than trial participants without diabetes.
Results are averages. Individual responses and tolerability vary, and stopping treatment may change outcomes.

What the evidence does not yet settle

Long-term safety across years of routine use.
Weight maintenance after discontinuation.
Head-to-head superiority over tirzepatide.
Definitive reductions in heart attacks, strokes, cardiovascular death or kidney failure.
Safety in pregnancy, breastfeeding, children and many high-risk clinical groups excluded from trials.
Final FDA indications, prescribing warnings, contraindications, dosing, price or insurance coverage.

Funding and conflicts matter

The major retatrutide trials were funded by Eli Lilly, and several papers include Lilly employees and shareholders as authors. Industry-sponsored randomized trials can be rigorous and informative, but readers should still distinguish journal articles from sponsor news releases and look for independent replication, regulatory review and post-approval surveillance.

Editorial rule used here: we quote trial numbers with the population, duration, dose and evidence status attached. We do not turn a trial average into a promise.

Next: put the benefits beside the risks.

See the adverse events reported so far, the unknowns and why gray-market products add risks the trials cannot measure.

Read safety and side effects Open all 15 sources

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