reviewed april 2026|next review october 2026|88 physicians psi has verified|131 published studies
Retatrutide
Retatrutide is an investigational triple-receptor agonist developed by Eli Lilly that activates GLP-1, GIP, and glucagon pathways simultaneously, with the first Phase III result reporting the largest weight loss ever recorded in a controlled clinical trial.
Evidence landscape: 131 published studies
131 published items: 38 animal studies and 12 human studies including the first Phase III trial result. An active commercial development program sponsored by Eli Lilly under the TRIUMPH Phase III program.
- 12 Human
- 38 Animal
- 81 Reviews
Investigational. Not FDA-approved and not approved by any major regulatory body. The first Phase III trial result is published. Eli Lilly is expected to file for FDA approval after the remaining Phase III trials read out.
Not available outside clinical trials. The TRIUMPH Phase III program is the only access route. A doctor cannot write a prescription for it through any pharmacy.
Three receptor pathways activated at once: GLP-1, GIP, and glucagon. The glucagon component drives energy expenditure and liver-fat oxidation, mechanisms not present in semaglutide or tirzepatide.
PSI Assessment
The first Phase III readout for retatrutide reported a 28.7% mean body weight reduction over 68 weeks. It is the largest weight loss outcome ever recorded in a controlled clinical trial. The compound is investigational, developed by Eli Lilly, and not available outside the TRIUMPH Phase III program. Six additional Phase III trials in the same program have not yet reported. An FDA submission has not been filed. A new safety signal of dysesthesia, an abnormal skin sensitivity, appeared at the highest dose. Whether it holds across the full program is the open question.
The strongest weight loss signal ever recorded in a clinical trial. And the program that produced it is not finished.
Retatrutide combines agonism at three receptors that current weight-loss medications target one or two of: GLP-1 (appetite suppression), GIP (insulin sensitivity and adipose tissue effects), and glucagon (energy expenditure and liver-fat oxidation). The glucagon arm is what no approved compound provides. It is the mechanistic reason results have been larger than the previous generation of GLP-1 and dual-agonist therapies.
What the evidence supports
The first Phase III trial of retatrutide reported 28.7% mean body weight reduction over 68 weeks. Phase II had reported 24.2%. The triple-receptor mechanism is pharmacologically validated, and the glucagon component adds energy expenditure that dual-agonist therapies do not provide.
What is not yet established
Six of the seven planned Phase III trials in the TRIUMPH program have not yet reported. FDA approval has not been filed. Long-term safety beyond Phase III trial duration is unstudied. The dysesthesia signal observed at higher doses in TRIUMPH-4 is new and not yet understood. Cardiovascular outcomes for retatrutide are entirely unstudied.
Research Evidence
Findings below add the comparative, safety, and diabetes context that the headline number does not carry.
Evidence by condition
Evidence dimensions across the conditions retatrutide is being studied for. Weight loss has the deepest evidence (Phase II + Phase III). Type 2 diabetes has Phase II only. Fatty liver disease (NAFLD/NASH) and muscle effects remain investigational or unstudied.
| Condition | Mechanism | Animal evidence | Human evidence | Replication |
|---|---|---|---|---|
| Weight loss | ||||
| Type 2 diabetes | ||||
| Fatty liver disease (NAFLD/NASH) | ||||
| Muscle growth |
The Jastreboff Phase II reported larger weight loss for retatrutide than published Phase III results for semaglutide or tirzepatide in their respective trials. No head-to-head trial of the three has been run.
Cross-trial comparisons are imperfect because populations and protocols differ. They are the best frame available until a head-to-head trial is funded and completed.
A new safety signal appeared in the TRIUMPH-4 Phase III. Dysesthesia, an abnormal skin sensitivity or tingling, was reported in up to 20.9% of patients at the highest dose, versus 0.7% on placebo. This signal was not present in Phase II.
Why dysesthesia appears at higher doses or in a larger sample is not yet understood. It will be tracked closely across the remaining six Phase III trials in the TRIUMPH program.
A separate Phase II trial in adults with type 2 diabetes reported substantial HbA1c reduction. The cohort was small and the result has not been replicated in a Phase III diabetes-specific trial.
If the diabetes signal holds in Phase III, retatrutide could land in the same metabolic-medicine category as semaglutide for both weight and glycemic control.
Lean mass preservation during rapid weight loss is an open question for the entire GLP-1 class. Retatrutide has not been specifically studied for muscle preservation, and the larger weight loss magnitude makes the question more pressing.
Whether the dramatic weight loss is accompanied by proportional lean mass loss will be a clinically important read-out from the remaining Phase III trials.
12 Human|38 Animal|81 Reviews
View all 131 indexed studiesHow Retatrutide Works
Retatrutide is a synthetic peptide engineered to activate three different hormone receptors simultaneously: GLP-1, GIP, and glucagon. Eli Lilly developed it as the first triple-receptor agonist to enter Phase III clinical development.
If semaglutide presses one button and tirzepatide presses two, retatrutide presses three. Simultaneously activating GLP-1, GIP, and glucagon receptors. That third receptor adds energy expenditure on top of appetite suppression, which may explain why weight loss results have been dramatically higher than previous generations.
For a more detailed view of the biology, here is what researchers have observed at the molecular level.
GLP-1 receptor agonism reduces appetite via hypothalamic signaling and enhances glucose-dependent insulin secretion from pancreatic beta cells. GIP receptor agonism improves insulin sensitivity and modifies adipose tissue metabolism. Glucagon receptor agonism, the distinguishing feature of retatrutide, increases hepatic fat oxidation and stimulates thermogenesis, raising energy expenditure. Tirzepatide adds GIP to a GLP-1 backbone. Retatrutide adds glucagon on top of both. The triple activation is the pharmacological basis for the larger weight-loss magnitude observed in Phase II and Phase III.
What is Retatrutide being studied for?
Researchers are studying Retatrutide across several health conditions. Each condition below is labeled with the strength of evidence that exists for that specific use, not for Retatrutide overall. This means a compound can have human studies for one condition but only animal data for another.
Weight loss
·Human TrialsFirst Phase III result reported 28.7% body weight reduction over 68 weeks. Phase II had reported 24.2% over 48 weeks. The trend is consistent and strengthening as the program advances.
Limitations: One Phase III trial in a single population (knee osteoarthritis cohort). Six additional Phase III trials in the TRIUMPH program are still reading out. Long-term weight maintenance after stopping treatment is not yet characterized.
Type 2 diabetes
·Human TrialsPhase II in adults with type 2 diabetes reported substantial HbA1c reduction with a dose-dependent response. Weight outcomes in the diabetes cohort were consistent with the obesity Phase II.
Limitations: Phase II sample size only. No Phase III diabetes-specific trial has reported. Long-term cardiovascular outcomes are entirely unstudied for retatrutide.
Fatty liver disease (NAFLD/NASH)
·PreclinicalThe glucagon receptor component is mechanistically expected to reduce liver fat. Sub-analysis of the obesity Phase II reported reductions in liver fat content, but no dedicated NASH trial has been published.
Limitations: Liver outcomes were secondary endpoints in a weight-loss trial. No dedicated hepatology Phase II or Phase III has been run.
Muscle growth
·PreclinicalRetatrutide is not studied for muscle growth. As with the broader GLP-1 class, lean mass preservation during rapid weight loss is an open clinical concern.
Limitations: No published data on muscle-specific outcomes. The question is open for the entire GLP-1 class.
Safety and Regulatory Status
FDA Status: Investigational. Not approved by the FDA or any major regulatory body. Eli Lilly is the sponsor. The TRIUMPH Phase III program is currently reading out across multiple indications.
Availability: Not available for prescription. The only access route is enrollment in an active TRIUMPH Phase III trial. Approval is expected to be filed after the remaining Phase III trials report results.
Class context: Retatrutide is the first triple-receptor (GLP-1, GIP, glucagon) agonist to reach Phase III. Tirzepatide and semaglutide, which are FDA-approved, target one or two of the same receptors but not all three.
Side effects in trials so far are dominated by gastrointestinal complaints (nausea, vomiting, diarrhea, constipation), consistent with the broader incretin drug class and typically dose-dependent. The TRIUMPH-4 Phase III introduced a new finding: dysesthesia, an abnormal skin sensitivity or tingling, in up to 20.9% of patients on the highest dose. This signal was not present in the Phase II program and is being tracked closely. Long-term safety beyond Phase III duration is not yet established.
Peptide Structure
Technical molecular data for researchers and clinicians.
Questions and Comparisons
Questions the evidence raises for a Retatrutide discussion.
Comparison and Related Research
Retatrutide is most often compared with the FDA-approved metabolic peptides semaglutide (single GLP-1) and tirzepatide (dual GLP-1 + GIP). Retatrutide's triple-receptor mechanism is mechanistically novel; the comparisons below outline how each differs.
Head-to-head comparisons
Full research comparisons covering Retatrutide and another peptide side by side.
Retatrutide vs Tirzepatide
Evidence-based comparison of tirzepatide (FDA-approved dual GIP/GLP-1 agonist) and retatrutide (investigational triple-receptor agonist in Phase III). SURMOUNT-1, TRIUMPH-4, head-to-head magnitude analysis, dysesthesia safety signal, and PSI assessment.
View full comparisonRetatrutide vs Semaglutide
Three-way comparison of semaglutide, tirzepatide, and retatrutide for metabolic health. Evidence levels, receptor mechanisms, clinical data, and research maturity analyzed.
View full comparisonRetatrutide vs Survodutide
The two most anticipated next-gen weight loss peptides. Retatrutide targets three receptors. Survodutide targets two. Both in Phase 3. Evidence compared.
View full comparisonRelated compounds
Frequently Asked Questions
References
Each citation links to the original study on PubMed, the U.S. National Library of Medicine database.
- 1.Phase II trial of retatrutide in 338 adults with obesity over 48 weeks. Reported up to 24.2% mean body weight reduction at the 12 mg dose, the strongest weight-loss signal published for a peptide therapeutic at that point.Jastreboff AM et al., 2023 in N Engl J Med. View on PubMed
- 2.Phase II trial of retatrutide in adults with type 2 diabetes. Reported substantial HbA1c reduction with a dose-dependent response. The first dedicated diabetes-population data for the compound.Rosenstock J et al., 2023 in Lancet. View on PubMed
- 3.Foundational preclinical characterization of retatrutide. Established balanced triple-receptor activity in cell-based assays and animal models, providing the pharmacological basis for the clinical program.Coskun T et al., 2022 in Cell Metab. View on PubMed
- 4.Sub-analysis of the obesity Phase II cohort showing reductions in liver fat content with retatrutide. Hepatic outcomes were a secondary endpoint, not from a dedicated MASLD trial.Sanyal AJ et al., 2024 in Nat Med. View on PubMed
- 5.First Phase III result for retatrutide. 445 participants over 68 weeks. Reported 28.7% mean body weight reduction at the 12 mg dose. Primary and key secondary endpoints met. New dysesthesia safety signal observed at higher doses.Eli Lilly, 2026 in Trial result publication. View on PubMed
Medical Disclaimer
This content is for educational and informational purposes only and does not constitute medical advice. The information presented reflects published research as indexed by PSI and should not be used to make treatment decisions. Always consult a qualified healthcare provider before starting, stopping, or modifying any treatment.