Retatrutide (LY3437943)

Overview and Mechanism of Action

Retatrutide (LY3437943) is an investigational therapeutic compound developed by Eli Lilly and Company. Pharmacologically, it is classified as a triple agonist targeting three separate receptors involved in metabolic regulation:

• Glucagon-like peptide-1 (GLP-1) receptor
• Glucose-dependent insulinotropic polypeptide (GIP) receptor
• Glucagon receptor

This multi-receptor mechanism is designed to engage multiple metabolic pathways simultaneously. Incretin hormones such as GLP-1 and GIP play known roles in insulin secretion and metabolic signaling, while glucagon receptor activation contributes to energy expenditure and hepatic metabolic pathways. Retatrutide remains an investigational drug, meaning its efficacy and safety profile are under evaluation in controlled clinical studies and it has not received regulatory marketing authorization. For detailed updates on the regulatory pathway, see the [regulatory status tracking page](/retatrutide/fda-approval).

Regulatory Status and Phase 3 Development

Retatrutide has reached Phase 3 development, with Eli Lilly and Company sponsoring global clinical trial programs designed to evaluate its effects across several clinical conditions, including obesity, overweight, type 2 diabetes mellitus, chronic kidney disease (CKD), and atherosclerotic cardiovascular disease (ASCVD).

In addition to randomized clinical trials, an expanded access program exists under identifier [NCT07629401](/trials/pre-approval-expanded-access-of-retatrutide-ly3437943-nct07629401) ("Pre-approval Expanded Access of Retatrutide (LY3437943)"), which is listed as available for patients with obesity and obesity-related complications.

Clinical Trial Programs

The clinical evaluation of retatrutide spans two major Phase 3 clinical trial families: the TRIUMPH program (focused primarily on weight management, knee osteoarthritis, obstructive sleep apnea, and cardiovascular/kidney outcomes) and the TRANSCEND program (focused on glycemic control and type 2 diabetes management).

TRIUMPH Clinical Trials

• [TRIUMPH-1 (NCT05929066)](/trials/triumph-1): Enrolled 2,335 adults with obesity or overweight, alongside subsets for knee osteoarthritis and obstructive sleep apnea. The primary endpoints measure percent change in body weight, changes in the Apnea-Hypopnea Index (AHI), and changes in the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) pain subscale score. Additional progress is noted in the [TRIUMPH-1 topline readout summary](/news/triumph-1-topline-readout).
• TRIUMPH-4 (NCT05931367): Completed trial evaluating retatrutide versus placebo in 445 participants with obesity, overweight, and knee osteoarthritis, measuring WOMAC pain scores and percent body weight changes.
• TRIUMPH-5 (NCT06662383): An active, non-recruiting study comparing retatrutide directly against the dual GIP/GLP-1 receptor agonist tirzepatide in 800 adults with obesity.
• [TRIUMPH-9 (NCT07357415)](/trials/triumph-9-nct07357415): Evaluates percent change in body weight in 600 participants living with obesity or overweight.
• [TRIUMPH-Outcomes (NCT06383390)](/trials/triumph-outcomes): A large-scale trial with 10,000 enrolled participants living with obesity and atherosclerotic cardiovascular disease or chronic kidney disease. Primary endpoints include time to composite cardiovascular endpoints and a composite kidney endpoint comprising end-stage kidney disease (ESKD), a sustained decline in estimated glomerular filtration rate (eGFR) of 40% or greater, cardiovascular death, or renal death.

TRANSCEND Clinical Trials

• TRANSCEND-T2D-1 (NCT06354660): Completed Phase 3 study evaluating change in glycated hemoglobin (HbA1c) versus placebo in 537 adults with type 2 diabetes managed with diet and exercise alone.
• TRANSCEND-T2D-2 (NCT06260722): Active, non-recruiting study comparing retatrutide to the GLP-1 receptor agonist semaglutide in 1,250 adults with type 2 diabetes inadequately controlled on metformin with or without an SGLT2 inhibitor.

Preclinical and Mechanistic Research

Beyond Phase 3 clinical studies, preclinical research has evaluated retatrutide in animal and cell models across several domains:

• Renal Fibrosis: Preclinical work published in *iScience* (PMID: 42630988) investigated the comparative effects of semaglutide, tirzepatide, and retatrutide in unilateral ureteral obstruction (UUO) and aged mouse models of non-diabetic renal fibrosis. Further details can be found in the [renal fibrosis research summary](/research/comparative-effects-of-semaglutide-tirzepatide-and-retatrutide-on-renal-fibrosis-42630988).
• Central Nervous System and Cognition: Research published in *Behavioural Brain Research* (PMID: 42385950) evaluated the effects of retatrutide on learning and memory pathways in streptozotocin-induced diabetic rat models, as documented in the [learning and memory research report](/research/effects-of-retatrutide-on-learning-and-memory-in-streptozotocin-induced-male-dia-42385950).
• Cardio-Kidney-Metabolic Disease: Primary clinical and review literature (e.g., PMID: 42682157; PMID: 42673585) contextualizes multi-receptor agonist therapies within broader management strategies for metabolic and cardio-renal dysfunction. See the [systematic review on receptor co-agonists](/research/efficacy-and-safety-of-glucagon-like-peptide-1-receptor-agonists-and-co-agonists-42673585) for broader context on co-agonist trials.

Unregulated Sourcing and Black Market Issues

Because retatrutide remains an investigational compound without regulatory approval, legitimate access is restricted exclusively to sanctioned clinical trials and authorized expanded access programs.

On August 12, 2026, Eli Lilly and Company announced the filing of six lawsuits against entities involved in the illegal black market distribution of unapproved products sold as retatrutide. Furthermore, scientific commentary published in *Drug and Alcohol Review* (PMID: 42559975) evaluated the composition and labelling accuracy of unregulated products sold under the name retatrutide in Australia, underscoring ongoing regulatory and clinical concerns surrounding unauthorized products.

For a general index of development updates, refer to the [Retatrutide Overview](/retatrutide).

Sources

• ClinicalTrials.gov: NCT07629401, NCT06383390, NCT07357415, NCT05929066, NCT05931367, NCT06662383, NCT06260722, NCT06354660.
• Eli Lilly and Company regulatory and corporate announcements (July 23, 2026; August 5, 2026; August 12, 2026).
• PubMed: 42385950 (*Behavioural Brain Research*), 42630988 (*iScience*), 42673585 (*Annals of Internal Medicine*), 42559975 (*Drug and Alcohol Review*), 42682157 (*Kidney Research and Clinical Practice*), 42556625 (*Pharmacological Research*), 42683980 (*Indian Journal of Pharmacology*), 42649514 (*Cardiovascular Diabetology*).