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Metabolic and fat loss
Retatrutide: How the Triple Agonist Works, What the Trials Show, and Where It Stands
The short answer
Retatrutide is an investigational weekly injection from Eli Lilly that activates three hormone receptors at once: GLP-1, GIP and glucagon. In the Phase 3 TRIUMPH-1 trial, people on the highest dose lost an average of 28.3% of body weight at 80 weeks. It is not FDA approved as of September 2026.
Questions people ask about Retatrutide
- What is retatrutide?
- Is retatrutide FDA approved?
- Is retatrutide a GLP-1?
- How much weight do people lose on retatrutide?
- Is retatrutide better than tirzepatide?
- What are the side effects of retatrutide?
- How does retatrutide work for weight loss?
- Is retatrutide made from venom?
- Is retatrutide legal to buy?
- When will retatrutide be available?
Retatrutide at a glance
| Also called | LY3437943; nicknamed “Reta” or informally “GLP-3” |
|---|---|
| What it is | Synthetic peptide; GLP-1, GIP and glucagon receptor triple agonist |
| Main system | Metabolic: appetite, insulin, energy expenditure |
| Evidence level | Late-stage human trials (Phase 3) |
| FDA status (Sept 2026) | Not approved; investigational |
| Developer | Eli Lilly and Company |
What is retatrutide?
Retatrutide is a lab-made peptide designed to hit three receptors involved in appetite and metabolism. The first generation of these drugs (semaglutide) targets one receptor. Tirzepatide targets two. Retatrutide adds a third, the glucagon receptor, which is why people call it a triple agonist.
It is taken as a once-weekly injection because its structure lets it bind to albumin in the blood, stretching its half-life to roughly six days (The Longevity Map, p. 89).
How does retatrutide work?
Each receptor does a different job, and the combination is the point (Metabolic Precision, pp. 105–106):
- GLP-1: boosts insulin release when blood sugar is high, slows stomach emptying and signals fullness to the brain.
- GIP: adds to insulin release and acts on how fat tissue handles energy.
- Glucagon: the new piece. It raises energy use in the liver, increases fat breakdown and burning. On its own glucagon would push blood sugar up, but the GLP-1 and GIP activity is designed to balance that.
The result is a drug that both lowers how much you eat and raises how much energy you burn, rather than only suppressing appetite.
Retatrutide trial results
Phase 2 (2023). In a 48-week trial published in the New England Journal of Medicine, participants on the highest dose lost an average of 24.2% of body weight (reference 1). A separate Phase 2 trial in people with type 2 diabetes showed large improvements in blood sugar and weight (reference 2).
Phase 3, TRIUMPH-1 (May 2026). In 2,339 adults with obesity or overweight and at least one weight-related condition, but without diabetes, the highest dose produced an average weight loss of 28.3% at 80 weeks, against 2.2% on placebo. In a group with a starting BMI of 35 or more, weight loss reached 30.3% at 104 weeks (reference 3).
Those are among the largest average weight-loss figures reported for any drug. They come from trials with medical supervision, gradual dose increases and monitoring, which is not the same thing as using an unregulated product.
Retatrutide side effects
The side effects look like the rest of the incretin class, mostly digestive and worst while the dose is being increased. At the highest dose in TRIUMPH-1 (reference 3):
- Nausea: 42.4%
- Diarrhoea: 32.0%
- Constipation: 26.1%
- Vomiting: 25.3%
- Stopped because of side effects: 11.3%, vs 4.9% on placebo
Because it is newer and adds glucagon signalling, its long-term safety record is shorter than that of semaglutide or tirzepatide. The books flag the same cautions as for the class, including thyroid precautions and the need to protect muscle during rapid weight loss (Metabolic Precision, p. 107; The Longevity Map, pp. 89–90).
Retatrutide vs tirzepatide vs semaglutide
Semaglutide (Ozempic, Wegovy) activates GLP-1 only. Tirzepatide (Mounjaro, Zepbound) activates GLP-1 and GIP; in its pivotal obesity trial, the top dose produced about 21% average weight loss at 72 weeks (reference 4). Retatrutide adds glucagon and has shown larger average losses in its trials.
Two cautions before calling it “better.” No head-to-head trial has compared retatrutide directly with tirzepatide, and trials with different lengths and populations can’t be compared precisely. And semaglutide and tirzepatide are approved medicines with years of real-world safety data. Retatrutide is not yet.
Is retatrutide legal? When will it be available?
Retatrutide is an investigational drug. In the U.S., the only legitimate way to receive it today is through a clinical trial. Products sold online as “research” retatrutide are not the Lilly drug, are not approved for human use and carry unknown quality risks.
Availability depends on FDA review of Lilly’s application after the Phase 3 program. No approval date has been set. This page will be updated when that changes.
Retatrutide: frequently asked questions
What is retatrutide?
Retatrutide is an investigational once-weekly injection from Eli Lilly that activates three hormone receptors: GLP-1, GIP and glucagon. It is being developed for obesity and related conditions.
Is retatrutide FDA approved?
No. As of September 2026 it is still investigational, although Phase 3 trials have reported strong results.
Is retatrutide a GLP-1?
Partly. It activates the GLP-1 receptor, but also GIP and glucagon receptors, which makes it a triple agonist. “GLP-3” is an informal nickname, not a medical term.
How much weight do people lose on retatrutide?
In the Phase 3 TRIUMPH-1 trial, the highest dose produced 28.3% average weight loss at 80 weeks, compared with 2.2% on placebo.
Is retatrutide better than tirzepatide?
Its trials have shown larger average weight loss, but no head-to-head trial exists, and tirzepatide is approved with far more real-world safety data.
What are the side effects of retatrutide?
Mostly digestive: nausea, diarrhoea, constipation and vomiting, most common while the dose is being increased. About 11% stopped for side effects at the highest dose in TRIUMPH-1.
How does retatrutide work for weight loss?
It reduces appetite and slows stomach emptying through GLP-1 and GIP, while glucagon activity raises energy use and fat burning, so it acts on both intake and expenditure.
Is retatrutide made from venom?
No. Retatrutide is a synthetic engineered peptide. The link to venom comes from exenatide, an earlier GLP-1 drug based on a hormone found in Gila monster saliva.
Is retatrutide legal to buy?
Not as an approved medicine. In the U.S. the legitimate route today is a clinical trial. Online “research” products are unapproved and of unknown quality.
When will retatrutide be available?
It depends on the FDA’s review of Lilly’s application following the Phase 3 program. No approval date has been announced.
Where Retatrutide appears in our books
This page is the plain-language overview. The books go further: mechanism detail, evidence tiers, how Retatrutide fits a full protocol, and the cautions that go with it. Page numbers refer to the print editions.
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Open the Protocol BuilderSee the book seriesReferences
- Jastreboff AM, Kaplan LM, Frías JP, et al. Triple-Hormone-Receptor Agonist Retatrutide for Obesity: A Phase 2 Trial. N Engl J Med. 2023;389(6):514–526. View sourceCited in Targeted Peptide Systems (p. 349), The Cognitive Advantage (p. 408), Metabolic Precision (p. 353) and The Longevity Map (p. 197)
- Rosenstock J, Frias J, Jastreboff AM, et al. Retatrutide, a GIP, GLP-1 and glucagon receptor agonist, for people with type 2 diabetes: a randomised, double-blind, placebo and active-controlled, parallel-group, phase 2 trial. Lancet. 2023;402(10401):529–544. View sourceCited in Metabolic Precision (p. 353)
- Eli Lilly and Company. Lilly’s triple agonist, retatrutide, delivered powerful weight loss in pivotal Phase 3 obesity trial. May 21, 2026. View source
- Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide Once Weekly for the Treatment of Obesity. N Engl J Med. 2022;387(3):205–216. View sourceCited in Metabolic Precision and The Longevity Map
How this page is maintained. Regulatory status and trial results change. We review this page against current sources and update it as new information becomes available; the date at the top shows the last review.
Educational information only, not medical advice. Retatrutide is discussed here for education. Nothing on this page is a recommendation to use it or a dosing guide. Talk to a qualified clinician before starting, stopping or combining any compound.