From Phase 1b to Phase 3: The Retatrutide Trial Archive

Before the data

This page covers what the clinical and laboratory studies on retatrutide have actually measured — doses administered, outcomes recorded, and limitations noted. Retatrutide is investigational, meaning every number here comes from a trial, not approved medical use. The compound has not been approved by any regulator. Its developer is Eli Lilly, and its Phase 3 TRIUMPH program is ongoing as of mid-2026.

The cardiometabolic angle is the focus of this site: weight, blood sugar, liver fat, blood pressure, lipids, and the kidney and cardiovascular outcome trials that will determine whether retatrutide's metabolic signal translates to reduced events in real-world populations. Think of this as the instrument readout — every figure logged to its source, every gap noted in plain view.

If you are new to this compound and want a plain-English overview before the data, the Retatrutide effects page and the index plain-language summary are the right starting point.

Phase 1b: first-in-human PK and tolerability

The Phase 1b first-in-human trial enrolled 72 adults with type 2 diabetes and established the foundational pharmacokinetics. Key findings:

• Half-life: approximately 6 days. The extended half-life — enabled by the C20 fatty-diacid albumin-binding acylation — supports once-weekly subcutaneous dosing and allows gradual dose escalation over weeks ^[4].
• Weight loss at highest dose: -8.96 kg (placebo-adjusted) over 12 weeks ^[4]. At an absolute -8.96 kg in 12 weeks with a first-in-human tolerability-focused design, the metabolic signal was clear early.
• Daily glucose reduction: -2.8 mmol/L at 3 mg ^[4].
• Tolerability: treatment-emergent adverse events (TEAEs) in 63% of participants, predominantly GI in character; no severe hypoglycemia; acceptable safety profile supporting Phase 2 advancement ^[4].

The Phase 1b established the dose-escalation feasibility and PK parameters — half-life, once-weekly schedule — that structured every subsequent trial design.

Phase 2 obesity trial: the -24.2% benchmark

The pivotal Phase 2 obesity trial (Jastreboff et al., N Engl J Med, 2023) enrolled 338 adults with obesity or overweight with comorbidity. Participants received once-weekly subcutaneous injections at 1, 4, 8, or 12 mg, with stepwise escalation. Key outcomes at 48 weeks:

• 12 mg arm: mean body-weight change -24.2% vs -2.1% with placebo ^[1].
• 8 mg arm: -22.8%; 4 mg arm: -17.3%; 1 mg arm: -8.7% ^[1].
• Nearly 20 cm waist circumference reduction at the highest dose ^[10].
• GI adverse events: dose-related, predominantly mild to moderate; nausea affected approximately 45% at 12 mg; 18% discontinued at that dose ^[1].
• Heart rate: dose-dependent increase peaking at 24 weeks, approximately 5-7 bpm at highest dose ^[1].

A 2025 review in Biomolecules described the -24.2% figure as a step-change relative to prior incretin therapies, situating retatrutide at a magnitude approaching bariatric surgery weight loss in a pharmacological vehicle ^[6]. A separate Cell review of multi-receptor drug advancement contextualized the triple-agonist architecture as the mechanism enabling the 20-30% weight-loss band that single and dual agonists had not reached ^[11].

The 2026 CKM syndrome review in Cardiology in Review added: 63% of participants reached ≥20% total body weight loss; systolic blood pressure fell by 8.79 mmHg ^[12].

Phase 2 type 2 diabetes trial: glycemic and metabolic outcomes

The Lancet Phase 2 diabetes trial (Rosenstock et al., 2023) enrolled 281 adults with type 2 diabetes. Retatrutide was administered at 0.5-12 mg once weekly with stepwise escalation versus placebo and active comparator. Key outcomes:

• HbA1c reduction at 12 mg: -2.02% vs -0.01% with placebo at 24 weeks ^[2]. HbA1c (glycated hemoglobin — a marker reflecting average blood glucose over three months) falling by over two percentage points represents a meaningful glycemic improvement.
• Body weight reduction: -16.94% vs -3.00% placebo at 36 weeks ^[2].
• Safety: mild-to-moderate GI AEs in 35%; no severe hypoglycemia; no deaths ^[2].

A 2025 analysis of lipid and metabolite profiles (Pearson et al., J Clin Endocrinol Metab, 2026) found higher retatrutide doses associated with reductions in triglycerides and insulin-resistance biomarkers. Changes in fatty acid oxidation cluster mediated 23.2% of the weight-reduction response in non-diabetic participants ^[13].

A 2025 study found ANGPTL3/8 reductions (proteins that inhibit fat-clearing enzymes) at 8 and 12 mg in type 2 diabetes and across all doses in the obesity cohort, with reductions paralleling decreases in triglycerides and LDL-C ^[15]. The glucagon receptor component is mechanistically implicated in this lipid-clearing pathway.

Phase 2 MASLD substudy: liver fat elimination

A dedicated substudy enrolled 98 participants with obesity or overweight and MASLD (metabolic dysfunction-associated steatotic liver disease — formerly called NAFLD, or non-alcoholic fatty liver disease) confirmed by MRI-PDFF (magnetic resonance imaging proton density fat fraction, a non-invasive measure of liver fat content) at ≥10% at baseline.

Key outcomes at 24 weeks:

• 12 mg: -82.4% relative liver-fat reduction; 8 mg: -81.4%; 4 mg: -57.0%; 1 mg: -42.9% vs +0.3% placebo ^[5].
• 86% of participants at 12 mg reached normal liver fat (<5%) at 24 weeks ^[5].
• Reductions were sustained to 48 weeks: -86.0% at 12 mg ^[5].

Sanyal et al. published these results in Nature Medicine in 2024. The liver-fat clearance rate is among the most striking single-organ findings in the retatrutide Phase 2 program — it suggests the glucagon-receptor-driven hepatic lipid metabolism arm is active at doses already producing maximal weight loss. A 2024 review in npj Metabolic Health and Disease positioned retatrutide among incretin-based therapies showing broad efficacy across MASLD, type 2 diabetes, obstructive sleep apnea, and cardiovascular risk factors ^[9].

Structural biology: cryo-EM confirmation of triple binding

Li et al. (Cell Discovery, 2024) resolved the cryo-EM structures of retatrutide bound to GLP-1R, GIPR, and GCGR in active signaling complexes, providing near-atomic confirmation of simultaneous triple-receptor engagement ^[3].

The structures revealed a key detail: the extracellular loop 1 (ECL1) of each receptor adopts different conformations when bound to retatrutide — a rigid alpha-helix at GLP-1R and GCGR, but a flexible loop at GIPR. This structural asymmetry helps explain the differential potency profile: retatrutide is approximately 8.9 times more potent at GIPR than native GIP (the endogenous hormone), but 0.3x at GCGR and 0.4x at GLP-1R versus their respective native ligands ^[3].

The result is a finely tuned pharmacological profile — high GIPR engagement for insulinotropic and adipose effects, with controlled GCGR activation to add thermogenic energy expenditure without hyperglycemia.

Cardiometabolic outcomes meta-analysis context

A 2025 meta-analysis of 29 randomized controlled trials (n=37,348 non-diabetic adults with overweight or obesity) examined GLP-1-based therapies across cardiovascular endpoints ^[7]. Across the class:

• Total cardiovascular events: RR 0.81 (19% relative reduction).
• MACE (major adverse cardiovascular events): RR 0.80.
• Myocardial infarction: RR 0.72.
• All-cause mortality: RR 0.81.

Retatrutide was specifically highlighted as most effective among agents at improving lipid profiles within the meta-analysis ^[7]. This is a class-level finding — retatrutide's own dedicated cardiovascular outcomes trial (NCT06383390) is ongoing and has not reported results. These meta-analysis findings are background context, not retatrutide-specific outcomes.

A 2026 systematic review and meta-analysis (Basile et al., Eur J Prev Cardiol) found triple agonists reduced systolic blood pressure by 6.6 mmHg and diastolic blood pressure by 2.1 mmHg, with all-cause mortality reduced by 18% (RR 0.82) and no excess hypoglycemia or pancreatitis observed ^[14].

Phase 3 TRIUMPH program: what remains unknown

The TRIUMPH Phase 3 program is the definitive test. Ongoing trials as of mid-2026:

• TRIUMPH-1/2/3 (obesity and T2D efficacy, primary endpoints expected 2026-2027)
• NCT06383390 (cardiovascular outcomes)
• NCT05929066 / TRANSCEND-CKD (chronic kidney disease outcomes)
• NCT05931367, NCT05882045 (active-comparator head-to-head with tirzepatide)

Unanswered questions the trials are designed to address: Does retatrutide reduce cardiovascular events in high-risk populations? What are the kidney effects at scale? What is the long-term durability of weight loss — and what happens when the compound is discontinued? How does it compare head-to-head with the current standard of care? This site will track published findings from these trials as they emerge.