Retatrutide Results in the Clinical Trials

The brief version on results

Retatrutide results from Phase 2 and Phase 3 trials are the reason this compound has attracted more clinical-development attention than any other investigational injectable compound in the obesity space. In Phase 2, it produced weight losses of up to -24.2% in 48 weeks ^[1] — a number that exceeds every prior approved once-weekly injectable in controlled trials. It cut liver fat by over 80% in fatty liver disease ^[5] and lowered blood sugar substantially in type 2 diabetes ^[2].

The first Phase 3 data confirmed the Phase 2 picture at larger scale and longer follow-up in a diabetes population ^[12]. Multiple outcome trials — for heart disease, kidney disease, and active comparison versus tirzepatide — are still running.

All the numbers are below, organized by trial. Retatrutide is not approved; these results are from controlled clinical studies, not commercial use.

Phase 1b results: pharmacokinetics and early weight loss

Trial: Phase 1b, multiple-ascending-dose (MAD), n=72 adults with type 2 diabetes, 12 weeks ^[4].

Primary finding: Half-life approximately 6 days, supporting once-weekly dosing. This PK result was the pharmacokinetic proof-of-concept for the entire weekly-dosing strategy.

Weight loss (placebo-adjusted): At the highest dose group, -8.96 kg over 12 weeks (90% CI -11.16 to -6.75 kg).

Glucose: Daily glucose reduced by -2.8 mmol/L at 3 mg.

Safety: Treatment-emergent adverse events in 63%, predominantly GI, mostly mild. No serious adverse events related to the compound. Acceptable safety profile confirmed for Phase 2 entry.

Phase 2 obesity results: -24.2% body weight at 48 weeks

Trial: Phase 2, randomized double-blind placebo-controlled, n=338 adults with obesity or overweight with comorbidity, 48 weeks, published NEJM 2023 ^[1].

Primary endpoint — mean body-weight change at 48 weeks:

| Dose | Mean weight change | vs Placebo (-2.1%) | |------|-------------------|--------------------| | 1 mg | -3.7% | -1.6 pp | | 4 mg | -8.7% | -6.6 pp | | 8 mg | -17.3% | -15.2 pp | | 12 mg | -24.2% | -22.1 pp |

Responder analysis at 12 mg:

• ≥5% weight loss: 100% of completers
• ≥10% weight loss: 91%
• ≥20% weight loss: 75%
• ≥30% weight loss: 26%

Adverse events:

• GI events (nausea, diarrhea, vomiting, constipation): dose-related, mostly mild to moderate
• Discontinuation due to AEs at 12 mg: 18%
• Dose-dependent resting heart rate increase peaking at week 24: mean +5–7 bpm at highest doses
• Injection-site reactions: ~8%

Phase 2 type 2 diabetes results: HbA1c -2.02%, weight -16.94%

Trial: Phase 2, randomized double-blind placebo and active-controlled, n=281 adults with type 2 diabetes, 36 weeks, published The Lancet 2023 ^[2].

Glycemic endpoint — HbA1c change at 24 weeks:

• 12 mg: -2.02% vs -0.01% placebo
• 8 mg: -1.83%

Weight endpoint at 36 weeks:

• 12 mg: -16.94% vs -3.00% placebo

Safety: Mild-to-moderate GI adverse events in 35%. No severe hypoglycemia in participants not on background insulin. No deaths. This trial confirmed the mechanism's dual glycemic-plus-weight profile is reproducible in a diabetes population.

Phase 2 MASLD results: liver fat -82.4% at 24 weeks

Trial: Phase 2a, randomized, n=98 adults with obesity/overweight and MASLD (≥10% liver fat by MRI-PDFF, no type 2 diabetes), 48 weeks, published Nature Medicine 2024 ^[5].

Liver fat change at 24 weeks (relative to baseline by MRI-PDFF):

• 12 mg: -82.4%
• 8 mg: -81.4%
• 4 mg: -57.0%
• 1 mg: -42.9%
• Placebo: +0.3%

Responders reaching normal liver fat (<5%) at 12 mg: 86%

Sustained to 48 weeks: -86.0% relative reduction at 12 mg.

This is the most striking single-endpoint result in the retatrutide dataset. The glucagon receptor arm's direct hepatic lipid metabolism effect, additive to weight-loss-driven fat clearance, accounts for the depth of the response — a mechanism absent from pure GLP-1 agents.

Phase 3 TRANSCEND-T2D-1 results: first Phase 3 readout (2026)

Trial: Phase 3, randomized double-blind placebo-controlled, n=537 adults with type 2 diabetes, 40 weeks, published The Lancet 2026 ^[12].

Primary endpoint — HbA1c reduction at 40 weeks:

• 12 mg: -1.94% vs -0.81% placebo

Secondary endpoint — body weight change:

• 12 mg: -15.3% vs -2.6% placebo

Safety:

• Discontinuation due to AEs: 8.5% at 12 mg vs 2.2% placebo
• No severe hypoglycemia
• Adverse events: predominantly mild-to-moderate GI

This is the first Phase 3 data for retatrutide. It confirms Phase 2 efficacy at Phase 3 scale in a diabetes population. TRIUMPH obesity trials and cardiovascular/kidney outcomes trials remain ongoing.

What the retatrutide results mean in context

The -24.2% weight loss at 48 weeks in Phase 2 is the headline. For comparison, the most efficacious approved once-weekly injectable compounds produced approximately 20–22% weight loss in their Phase 3 pivotal trials at highest doses. Retatrutide's Phase 2 data exceed that; Phase 3 obesity data are still pending.

The 86% normal-liver-fat responder rate at 12 mg in MASLD is equally striking — liver fat below 5% is the diagnostic threshold for normal liver, and clearing that in 86% of trial participants at 24 weeks is a result with no near precedent in the pharmacological literature.

A 2025 expert review of the obesity pipeline concluded that retatrutide achieves weight reduction currently unmatched by any approved oral or injectable agent and characterized it as approaching bariatric surgery outcomes ^[8]. A 2026 review identified weight regain on discontinuation as the class-level limitation shared with other GLP-1-based therapies — not yet studied specifically for retatrutide long-term ^[14].

All these figures are from controlled trials under clinical supervision. Retatrutide results in a research-labeled, unmonitored context cannot be assumed to replicate these numbers.