Retatrutide

The Retatrutide evidence base cited here is 17 sources — 9 clinical, 1 preclinical, 4 review, 1 regulatory. Its strongest evidence is human — 9 clinical studies, most recently 2026 ("TRIUMPH-1 Pivotal Phase 3 Obesity Trial — 28.3% Weight Loss at 12 mg (To…"). Regulatory status: Not FDA-approved (Phase III).

Cross-trial comparison only — these drugs have not been tested head-to-head, and the populations, durations, and endpoints differ.

*The 28.3% figure is company-reported topline from the pivotal Phase 3 TRIUMPH-1 trial (12 mg, 80 weeks) and is pending peer-reviewed publication. The 24.2% figure is the peer-reviewed Phase 2 result (NEJM 2023). All three drugs are built on the same His-Aib-Glu-Gly-Thr-Phe… N-terminal incretin backbone — what differs is the receptor targets (GLP-1 → +GIP → +glucagon), the fatty-acid chain and half-life (~7 / ~5 / ~6 days), and the peak efficacy shown above.

• Retatrutide (LY3437943) is an investigational triple-receptor agonist from Eli Lilly that activates the GLP-1, GIP, and glucagon receptors simultaneously — a mechanism no approved drug shares.
• The strongest peer-reviewed result is a 24.2% mean body-weight reduction at 48 weeks in the Phase 2 obesity trial (Jastreboff et al., NEJM 2023).
• The pivotal Phase 3 obesity trial TRIUMPH-1 (n=2,339, 80 weeks) reported even larger topline results: 28.3% mean weight loss at the 12 mg dose vs 2.2% placebo, with 45% of participants losing ≥30% of body weight — putting it in bariatric-surgery territory. A BMI≥35 subset reached 30.3% at 104 weeks. Company-reported topline, pending peer-reviewed publication.

Retatrutide is an experimental peptide that Eli Lilly is developing for obesity, type 2 diabetes, and related metabolic disease. What sets it apart from the GLP-1 drugs already on the market is that it engages three metabolic receptors at once — GLP-1, GIP, and glucagon — rather than one or two.

In the peer-reviewed Phase 2 obesity trial, the top dose produced a 24.2% mean reduction in body weight at 48 weeks. Reported Phase 3 topline data describe even larger effects, but those figures have not yet been published in a peer-reviewed journal and should be read as preliminary. In cross-trial terms the Phase 2 result already exceeds the published ceilings for semaglutide (~15%) and tirzepatide (~22.5%), though no head-to-head trial has been run, so those comparisons carry the usual caveats about differing populations and endpoints.

Because it is still investigational, there is no FDA-approved label, no commercial formulation, and no approved dosing. Everything below is drawn from clinical-trial data and is presented for research context only — not as medical guidance.

Retatrutide (development code LY3437943) is a 39-amino-acid peptide built on a GIP-peptide backbone and conjugated to a C20 fatty-diacid chain that lets it bind albumin and circulate for days. Substitutions such as 2-aminoisobutyric acid (Aib) at positions 2 and 13 protect it from DPP-4 degradation, which is what makes once-weekly dosing possible (half-life ≈ 6 days; steady state reached in roughly 4–5 weeks at each dose level). By mass it is a ~4,731 Da peptide; after a subcutaneous dose plasma levels peak at about 1 day and the compound is largely cleared within roughly 30 days.

Its receptor activity is GIP-primary. Reported EC50 values are about 0.064 nM at the GIP receptor (its most potent target), 0.78 nM at GLP-1, and 5.8 nM at glucagon. Combining all three signals in one molecule is the central bet of the program: each receptor contributes a different metabolic lever, and together they appear to do more than single- or dual-agonists can.

There is no FDA-approved dosing for retatrutide. The figures below are the doses studied in trials, included for research context only.

Phase 2 used a dose-ranging design from 0.5 mg up to 12 mg once weekly, with escalation every 4 weeks. Even the 1 mg arm produced clinically meaningful loss (-8.7% at 48 weeks), while the 4, 8, and 12 mg arms scaled up from there. The Phase 3 TRIUMPH program standardized a 4-week step titration (2 → 4 → 6 → 8 → 10 → 12 mg), reaching the top dose by about week 20.

• 1 mg / week — low-dose Phase 2 arm: −8.7% body weight at 48 weeks
• 4 mg / week — −17.1% at 48 weeks
• 8 mg / week — Phase 2 high-dose arm
• 12 mg / week — maximum dose studied: −24.2% at 48 weeks

Across the program, slow escalation from the lowest dose is the consistent strategy for limiting gastrointestinal side effects. Weight-loss curves had not plateaued at 48 weeks, suggesting effects continue with longer treatment.

Mean body-weight reduction by dose, from the NEJM 2023 Phase 2 obesity trial:

• Week 24 — 12 mg: −17.5% · 8 mg: −17.3% · 4 mg: −12.9%
• Week 48 — 12 mg: −24.2% · 8 mg: −22.8% · 4 mg: −17.1%

The profile is typical of incretin-based therapies, dominated by gastrointestinal effects that appear during dose escalation and are mostly mild to moderate.

Dysesthesia is the safety signal worth watching as the program advances — at ~21% it is not rare, though most cases are mild and self-limiting, and whether titration can reduce it without losing efficacy is an open question for the NDA.

Published data on combining retatrutide with other compounds is limited. Because it already engages three metabolic pathways, it is designed to work as a standalone agent rather than part of a stack. The notes below are research context, not protocol advice.

• Other GLP-1 agonists — not advisable; overlapping mechanisms raise GI-side-effect risk with little added benefit.
• Metformin — trials included participants on stable metformin, and the combination was well tolerated.
• Lifestyle (diet, resistance training, adequate protein) — trials paired the drug with diet and activity guidance; resistance training plus higher protein intake is the evidence-based way to limit the lean-mass loss seen with rapid weight reduction.

No retatrutide-specific interaction studies are published; the considerations below are inferred from GLP-1-class pharmacology and are research context, not medical guidance.

• Insulin and sulfonylureas — additive hypoglycemia risk; trials reduced background doses and monitored glucose closely.
• Oral medications, including oral contraceptives — delayed gastric emptying can slow or reduce absorption; timing and effectiveness monitoring are the standard precautions.
• Warfarin and other narrow-therapeutic-index drugs — changing food intake and weight can shift dosing requirements; INR/levels warrant monitoring.
• Other GLP-1 / incretin agonists (semaglutide, tirzepatide) — overlapping mechanisms; combining is not advisable.

No commercial formulation exists, so the following reflects general lyophilized-peptide handling for laboratory research only.

• Lyophilized powder: store at −20°C long-term; stable at 2–8°C for shorter periods; protect from light.
• Reconstitute by adding bacteriostatic water down the vial wall and swirling gently (do not shake); inspect for full dissolution.
• Reconstituted solution: refrigerate at 2–8°C, use within ~28–30 days, protect from light, do not freeze.

The retatrutide evidence base spans peer-reviewed publications and company-reported topline readouts. Peer-reviewed results are the higher-confidence tier; topline figures are preliminary until published.

• Phase 2 obesity — Jastreboff et al., NEJM 2023 (n=338, 1–12 mg, 48 wk): 24.2% mean weight loss at 12 mg, no plateau at 48 weeks. Peer-reviewed.
• Phase 2 type 2 diabetes — Rosenstock et al., Lancet 2023 (n=281, 0.5–12 mg, 36 wk): ~16.9% weight loss and roughly two-point HbA1c reductions. Peer-reviewed.
• MASLD / liver-fat substudy — Nature Medicine 2024 (8–12 mg, 24 wk): large reductions in liver fat (reported on the order of ~80%+), with most higher-dose participants reaching normalization. Peer-reviewed substudy.
• Phase 1 pharmacokinetics — Cell Metabolism 2022 (single ascending dose): established the ~6-day half-life that supports once-weekly dosing. Peer-reviewed.
• TRIUMPH-1 (pivotal obesity, n=2,339, 80 wk): 28.3% at 12 mg — company-reported topline, pending publication.
• TRIUMPH-4 (obesity + knee osteoarthritis, 68 wk): ~28.7% weight loss with substantial osteoarthritis pain reduction — company-reported topline, pending publication.
• TRIUMPH-Outcomes (cardiovascular, ~10,000 participants with established ASCVD, ~5-year): assessing major adverse cardiovascular and kidney events — ongoing.

Cross-trial figures are not head-to-head and differ in population, dose, and duration. Treat any unpublished topline number as provisional.

Retatrutide is not approved by the FDA or any regulatory agency. It is in active clinical development by Eli Lilly across three program families — TRIUMPH (obesity), TRANSCEND (type 2 diabetes), and SYNERGY (liver disease) — spanning roughly 19 trials and ~19,700 participants.

• TRIUMPH-1 (pivotal obesity, no diabetes, n=2,339): reported topline May 2026 — 28.3% mean weight loss at 12 mg over 80 weeks vs 2.2% placebo; pending publication
• TRIUMPH-4 (obesity + knee osteoarthritis): completed Dec 2025 — reported topline ~28.7% at 68 weeks, pending publication
• TRANSCEND-T2D-1 (type 2 diabetes): completed Mar 2026 — reported topline, pending publication
• TRIUMPH-2/3 and cardiovascular- and liver-outcome trials: ongoing through 2026 and beyond
• Projected NDA filing: ~Q4 2026–Q1 2027
• Most-cited approval estimate: late 2027 or 2028

Research-grade retatrutide sold by peptide suppliers is for laboratory research only and is not intended for human use.

Retatrutide is not explicitly named on the 2026 WADA Prohibited List. However, GLP-1-class drugs have been on WADA's monitoring program since 2024, and an investigational metabolic agent like this could plausibly fall under metabolic-modulator or peptide-hormone categories. Athletes subject to testing should clear any use with their governing body first.

On the Huberman Lab podcast, Dr. Abud Bakri placed retatrutide in the GLP-1 family that he believes could help relieve a strained medical system — while repeatedly asking 'is there a free lunch?' He emphasized that these drugs raise GLP-1 signaling on the order of 1000-fold (versus 2–4× for older diabetes drugs), with unknown effects on neuroplasticity and learning, especially in young people losing large amounts of weight.

On the widely-discussed 'anhedonia / loss of drive' reports (e.g. Sam Altman's account), his view was that much of it may be misuse confounders — over-dosing, eating one meal a day, low blood sugar and blood pressure, and the loss of eating's social/pleasure role — rather than a direct receptor effect, and that clinician-guided dosing matters.

Expert clinical opinion; retatrutide is not FDA-approved, and the trial-efficacy figures elsewhere on this page are company-reported topline, pending peer review.

All citations link to the original source (PubMed, journal site, or regulatory filing). Independent research database — no vendor influence on what's cited.