Retatrutide
| Category | Metabolic & GLP-1 |
| Goals | Fat Loss |
| Evidence level | Clinical (Phase 2 complete; Phase 3 reporting — investigational) |
| Legal status | Investigational — not approved for any use |
| FDA status | Not approved; Phase 3 TRIUMPH program |
| Half-life | ~6 days (once-weekly) |
| Routes | Subcutaneous |
| CAS / MW / Sequence | 2381089-83-2 · ~4731 g/mol (approx) · triple-agonist peptide (complex) |
| Last reviewed | 2026-06-07 |
In one line
An investigational once-weekly “triple-G” GIP/GLP-1/glucagon receptor agonist showing the largest weight-loss figures yet seen in obesity trials — up to ~30% mean body weight.
Evidence at a glance
Retatrutide is investigational and not FDA-approved. It has strong but still-maturing human data: a completed Phase 2 obesity trial and the Phase 3 TRIUMPH program (TRIUMPH-1 topline results reported up to ~30% weight loss). Long-term safety and final regulatory status are not yet established. See Evidence Grading Explained and the Disclaimer.
Key Takeaways
- A first-in-class triple agonist — activates the GIP, GLP-1, and glucagon (GCGR) receptors simultaneously.
- Phase 2 (48 wks): up to ~24% mean weight loss at the highest dose, with no apparent plateau.
- Phase 3 TRIUMPH-1 (n=2,339): ~28.3% mean loss at 12 mg over 80 weeks, with 45.3% of that arm losing ≥30% — bariatric-surgery territory; up to ~30.3% at 104 weeks in a baseline-BMI-≥35 extension subgroup.
- The glucagon component may add energy expenditure and liver-fat reduction beyond GIP/GLP-1 agents.
- Not available as an approved medicine; anything sold now is gray-market/research material with no quality assurance.
What Is It
Retatrutide (development code LY3437943, Eli Lilly) is a synthetic peptide engineered to activate three metabolic receptors at once — GIP, GLP-1, and glucagon. Adding glucagon-receptor agonism to the dual-incretin approach is intended to raise energy expenditure and reduce hepatic fat, on top of the appetite-suppression and glycemic effects of GIP/GLP-1. It is administered as a once-weekly subcutaneous injection and is currently in late-stage (Phase 3) development for obesity, type 2 diabetes, osteoarthritis-related outcomes, and metabolic liver disease.
Mechanism of Action
Retatrutide is a triple receptor agonist (clinical):
- GLP-1 receptor — glucose-dependent insulin secretion, glucagon suppression, slowed gastric emptying, appetite reduction.
- GIP receptor — additional insulinotropic effect; proposed contributions to weight loss and GI tolerability.
- Glucagon (GCGR) receptor — increases energy expenditure and promotes hepatic fat oxidation, a mechanism absent from mono- and dual-incretin agonists.
Why add glucagon?
Glucagon raises metabolic rate and mobilizes liver fat. Balancing it against the incretin arms (which improve glycemia) is the design challenge; retatrutide is engineered to harness glucagon’s energy-expenditure benefit without worsening glucose control.
Evidence by Outcome
| Outcome | Evidence | Notes |
|---|---|---|
| Weight loss (obesity) | Clinical | Phase 2: up to ~24% at 48 wks; TRIUMPH-1: ~28.3% at 80 wks (12 mg) |
| Extended weight loss | Clinical | TRIUMPH-1 extension (baseline BMI ≥35): ~30.3% mean loss at 104 weeks |
| Glycemic control (T2D) | Clinical | Phase 3 reported significant A1C and weight reductions |
| Osteoarthritis / function | Clinical | TRIUMPH-4: large weight loss plus pain/physical-function improvement |
| Cardiovascular risk markers | Clinical | Improved waist circumference, lipids, BP, hsCRP in trials |
| MASLD / liver fat | Clinical/Preclinical | Marked hepatic-fat reduction reported; glucagon-driven mechanism |
| Long-term safety | Clinical (incomplete) | Not yet established; dose-dependent heart-rate increase noted |
Reported Dosing
Not medical advice
Retatrutide is investigational — there is no approved or established therapeutic dose. The figures below are trial doses only, not a protocol. See Reconstitution & Dosing Math.
| Context | Dose (trials) | Frequency | Notes |
|---|---|---|---|
| Phase 2/3 escalation | Started low, titrated upward | Once weekly | Slow escalation to limit GI effects |
| Highest trial arms | up to 12 mg (obesity) | Once weekly | Highest doses gave greatest weight loss |
Pharmacokinetics
Retatrutide shows dose-proportional pharmacokinetics with a half-life of ~6 days, supporting once-weekly subcutaneous dosing. Detailed human PK parameters beyond this are still being characterized in trials. See Half-Life & Pharmacokinetics.
Side Effects & Risks
- Gastrointestinal — nausea, diarrhea, vomiting, constipation; dose-dependent, most common during escalation (consistent with the incretin class).
- Increased heart rate — a dose-dependent rise has been observed, likely related to the glucagon component; under active monitoring in trials.
- Possible transient effects on glucose — the glucagon arm theoretically opposes glycemic lowering; balanced by the incretin arms in trial data.
- Long-term safety is unknown — no approval, no post-marketing surveillance; durability and rare-event risks not yet established.
- Sourcing risk is severe — because there is no approved product, all material on the gray market is unverified “research” peptide with no identity/purity guarantee. See Sourcing, Red Flags & Scams.
- See Side Effects & Risk Management and Bloodwork & Monitoring.
Cycling
There is no established clinical use, and therefore no evidence-based cycling guidance. As an investigational chronic metabolic therapy, any “cycling” framing is unsupported. See Cycling.
Stacks It Appears In
- None established. Retatrutide is studied as monotherapy in trials; combining an unapproved investigational agent with other compounds has no safety basis.
Comparisons
Sourcing & Quality
There is no FDA-approved retatrutide product, so no quality-assured legitimate source exists outside a clinical trial. Material sold online as “retatrutide” is gray-market research peptide of unverified identity and purity, carrying the highest sourcing risk in this category. Learn to evaluate quality and recognize scams before trusting any product: How to Read a CoA, Red Flags & Scams, Sourcing. Reconstitution/storage references: Reconstitution & Dosing Math, Storage & Handling. No vendors are endorsed here.
Legal & Regulatory Status
(As of 2026-06-07.) Not FDA-approved for any indication. Retatrutide is an investigational drug in Eli Lilly’s Phase 3 TRIUMPH program (obesity, type 2 diabetes, osteoarthritis, and related outcomes). Positive topline Phase 3 results (TRIUMPH-1) have been reported via investor release, and Lilly has indicated a regulatory submission anticipated in late 2026/early 2027 as the data package matures — but there is no marketing authorization yet. Because it is unapproved, it is not a lawful compounding substance and is not legally available as a medicine. Status in tested sport and across jurisdictions should be assumed restricted. See Regulatory & Legal Status.
FAQ
Is retatrutide approved? No. It is investigational and in Phase 3 trials; it is not approved for sale or prescription.
When might it be approved? Lilly has signaled a regulatory submission is anticipated in late 2026/early 2027 as the full data package matures. Any approval would follow FDA review after that — so it is not expected to be a marketed medicine in the near term. Timelines are estimates and can change.
How much weight loss does it cause? In Phase 3 TRIUMPH-1, the 12 mg dose produced ~28.3% mean loss at 80 weeks and ~30.3% in a 104-week extension — the largest figures reported for an obesity drug to date.
How is it different from tirzepatide? Retatrutide adds a third target — the glucagon receptor — to the GIP/GLP-1 mechanism, which may add energy expenditure and liver-fat reduction. See Tirzepatide vs Retatrutide.
Where can I get it legally? Only via participation in an authorized clinical trial. There is no approved product; online “research” sources are unverified.
References
- Jastreboff A.M. et al. (2023). “Triple–Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial.” New England Journal of Medicine.
- Rosenstock J. et al. (2023). “Retatrutide, a GIP/GLP-1/glucagon receptor agonist, in type 2 diabetes: a Phase 2 trial.” The Lancet.
- Eli Lilly and Company (2025–2026). TRIUMPH-1 Phase 3 topline results — n=2,339; 28.3% mean loss at 12 mg/80 wks, 45.3% achieving ≥30%; investor release. investor.lilly.com
- Structural and pharmacology reviews of retatrutide triple agonism at GLP-1R/GIPR/GCGR (e.g., Nature Communications, 2024).
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