Gathering the record
Relay is organizing the evidence and source boundaries.
GIP / GLP-1 / glucagon triple receptor agonist
Retatrutide is an investigational once-weekly triple agonist being studied for obesity, type 2 diabetes, and related complications. Human trials show substantial group-level effects on weight and metabolic outcomes, but it is not an approved medicine.
60-Second Overview
Start with what it is, why it matters, what research has shown, and what remains unknown. The science follows after the orientation.
Start here. These four answers explain why the compound matters before the page introduces the deeper science.
Retatrutide is an investigational medicine designed to influence three hormone signals involved in appetite, blood-sugar regulation, and energy use.
Researchers want to know whether addressing all three signals can change weight and metabolic health differently from medicines that address one or two. They are also examining liver fat, diabetes risk, cardiovascular outcomes, and whether findings persist across different groups.
Controlled human trials have reported substantial average weight reduction and improvements in blood-sugar measures in the populations studied. A smaller substudy also found large reductions in liver fat.
Retatrutide is not approved. Long-term cardiovascular outcomes, rare harms, durability after treatment ends, and complete results from the large confirmatory obesity program remain unresolved.
The research depth, routes, studies, and primary sources below explain how Relay knows—and where the evidence stops.
Research context
Published research has investigated this compound using the following study designs.
These records explain what researchers did. They are not instructions, recommendations, or a transferable protocol.
A randomized Phase 2 trial evaluated sponsor-controlled retatrutide in adults with obesity or overweight and a weight-related condition, without diabetes.
Reported study administration—not a recommendation.
Research at a glance
Evidence depth, confidence, and route context explain how Relay knows—not what anyone should do.
Phase 1 through Phase 3 research across several metabolic outcomes.
Research depth describes how large and mature the overall record is. It does not tell you whether the results were positive.
Controlled trials are consistent, while long-term outcomes and full pivotal reporting remain incomplete.
Confidence describes how reliable and consistent the conclusions are. It can be high for one outcome and low for another.
The strongest evidence type shows what the best-supported conclusions are actually based on.
Human findings are more directly relevant than animal or laboratory results, but they still apply only to the populations and outcomes studied.
Route-specific record
These are exposures used in cited research for a specific route and population—not an instruction for an individual.
Half-life describes how long it takes the measured amount in the body to fall by half. It is not a dosing recommendation.
Evidence can change by administration method. Findings from one route should not automatically be applied to another.
Evidence boundary: The study describes randomized trial arms; it does not select an amount for an individual. The publications do not establish a bacteriostatic-water volume, final concentration, post-reconstitution stability period, or equivalence to independently sourced material. Amounts shown describe cited research exposure—not a dosage recommendation.
Detailed evidence
Start with the strongest supported conclusion and its main uncertainty. Claim-level records below show how the evidence changes by question, population, route, formulation, and study design.
A 537-participant, randomized, double-blind Phase 3 trial in type 2 diabetes was published in The Lancet in June 2026. Multiple larger obesity Phase 3 trials have positive topline results, but full peer-reviewed reports were not yet located at the cutoff.
This is the strongest supported conclusion in the current human evidence—not a summary of every claim made about the compound.
Long-term cardiovascular, renal, and rare-event safety; durability after discontinuation; and full peer-reviewed reporting from the pivotal obesity program.
Keeping the main uncertainty visible prevents an early or promising finding from looking more settled than it is.
Questions people bring to the evidence
Research questions—not promises of benefit.
It is a triple agonist, not “GLP-3.” Each receptor pathway has different metabolic effects, but a receptor mechanism alone does not prove a clinical outcome.
Peer-reviewed Phase 2 trials and a peer-reviewed Phase 3 diabetes trial reported group-level changes in weight and glucose-related outcomes.
In 98 participants with at least 10% liver fat, all studied retatrutide groups had greater mean liver-fat reduction than placebo at week 24.
Across controlled studies, nausea, diarrhoea, constipation, and vomiting were commonly reported, often during escalation.
Positive trial results do not equal approval. Lilly states that a U.S. application is planned for Q1 2027.
Published trial arms describe study administration, not instructions for unsupervised use. Trial material is sponsor-controlled.
Mechanisms
Retatrutide (LY3437943) is a 39-amino-acid, long-acting single peptide with agonist activity at the GIP, GLP-1, and glucagon receptors. The clinical program spans obesity, type 2 diabetes, knee osteoarthritis pain, obstructive sleep apnoea, cardiovascular and renal outcomes, and MASLD. As of July 24, 2026, the evidence base includes peer-reviewed Phase 1b and Phase 2 trials, one full peer-reviewed Phase 3 diabetes trial, and multiple sponsor-reported Phase 3 topline readouts awaiting full publication.
A plausible mechanism can explain why a study was attempted. It does not prove that the compound improves a human outcome.
Studies
Study arms are reported for transparency. They describe what researchers did in a defined record and do not transfer across identities, routes, formulations, or populations.
A later trial phase can ask a more mature question, but it does not guarantee a positive result, regulatory approval, or relevance outside the studied population.
Randomized, double-blind, placebo-controlled, multicenter trial
Adults with type 2 diabetes inadequately controlled by diet and exercise; HbA1c 7.0–9.5%; BMI at least 23 kg/m²
Mean HbA1c fell 1.69–1.94 percentage points with retatrutide versus 0.81 with placebo. Mean body-weight change was −11.5% to −15.3% versus −2.6% with placebo.
Study administration: Once-weekly subcutaneous retatrutide 4 mg, 9 mg, or 12 mg, or placebo (trial arms; not prescribing guidance)
Limitations: Monotherapy population with relatively short diabetes duration; 40 weeks does not establish long-term cardiovascular or renal outcomes. Sponsor funded, with several authors employed by the sponsor.
Randomized, double-blind, placebo-controlled MRI substudy nested in the Phase 2 obesity trial
Participants with at least 10% liver fat by MRI-PDFF within the Phase 2 obesity trial
At week 24, mean relative liver-fat change was −42.9%, −57.0%, −81.4%, and −82.4% across the four retatrutide groups versus +0.3% with placebo.
Study administration: Once-weekly subcutaneous retatrutide 1 mg, 4 mg, 8 mg, or 12 mg, or placebo
Limitations: Small imaging-defined substudy; fewer MRI observations at week 48; not a biopsy-based liver-outcomes trial; population was 98% White.
Randomized, double-blind, placebo- and active-controlled parallel-group trial
Adults aged 18–75 with type 2 diabetes
Retatrutide produced dose-dependent improvements in glycaemic control and body weight. At week 36, mean weight change reached about −16.9% in the highest-dose groups versus −3.0% with placebo and −2.0% with dulaglutide.
Study administration: Multiple once-weekly subcutaneous retatrutide trial arms, placebo, and dulaglutide 1.5 mg active control
Limitations: Phase 2 duration and size; the active comparator dose and design do not support broad cross-drug ranking.
Phase 2, multicenter, randomized, double-blind, placebo-controlled, parallel-group, dose-ranging trial.
Adults with obesity (BMI ≥30) or overweight (BMI 27 to <30) with at least one weight-related condition, without type 2 diabetes.
In this 338-participant Phase 2 trial, every retatrutide maintenance-dose group had greater average weight reduction than placebo at 24 weeks. At 48 weeks, average weight change ranged from −8.7% in the 1 mg group to −24.2% in the 12 mg group, compared with −2.1% with placebo. Gastrointestinal adverse events were the most commonly reported and occurred primarily during dose escalation. Dose-dependent increases in heart rate were also observed.
Study administration: Once-weekly subcutaneous retatrutide maintenance doses of 1, 4, 8, or 12 mg, using different dose-escalation schedules in some groups, compared with placebo. All groups received standardized diet and physical-activity counseling.
Limitations: This was a sponsor-funded Phase 2 trial lasting 48 weeks. The individual treatment groups were relatively small, and the study was not designed to establish uncommon or long-term safety outcomes. Participants did not have type 2 diabetes, so the findings should not automatically be generalized to every population. Study interventions describe the trial design and are not dosing recommendations.
Multicenter, double-blind, randomized, placebo-controlled multiple-ascending-dose trial
Adults with type 2 diabetes using metformin
The study established early human pharmacology, dose-proportional exposure, a half-life compatible with weekly study administration, and signals for glucose and weight change.
Study administration: Multiple once-weekly subcutaneous ascending-dose regimens, placebo, and dulaglutide
Limitations: Small, short, early-phase study designed primarily for safety and pharmacology, not durable clinical outcomes.
Two randomized, double-blind, placebo-controlled trials
TRIUMPH-2: adults with obesity or overweight and type 2 diabetes. TRIUMPH-3: adults with severe obesity and established cardiovascular disease, with or without type 2 diabetes.
On July 23, 2026, Lilly reported up to 20.8% mean weight loss in TRIUMPH-2 and up to 22.6% in TRIUMPH-3 at 80 weeks.
Study administration: Retatrutide trial arms versus placebo
Limitations: Sponsor-reported topline release issued one day before this review cutoff; detailed results and peer-reviewed reports were not yet available.
Randomized, double-blind, placebo-controlled master trial
Adults with obesity or overweight plus at least one weight-related comorbidity, without diabetes
Sponsor-reported efficacy-estimand results showed mean weight changes of −19.0%, −25.9%, and −28.3% across retatrutide doses versus −2.2% with placebo at week 80.
Study administration: Once-weekly subcutaneous retatrutide 4 mg, 9 mg, or 12 mg, or placebo
Limitations: Sponsor-reported topline results presented at a meeting; a full peer-reviewed report was not located by the July 24, 2026 evidence cutoff.
Randomized, double-blind, placebo-controlled trial
Adults with obesity or overweight and knee osteoarthritis, without diabetes
Sponsor-reported results showed mean weight change up to −28.7% and mean WOMAC pain-score reduction up to 4.5 points at 68 weeks.
Study administration: Once-weekly retatrutide 9 mg or 12 mg, or placebo
Limitations: Topline sponsor report without a peer-reviewed full publication located by the cutoff. The sponsor release appears to print an incorrect NCT number; registry and Lilly trial records identify NCT05931367.
Safety snapshot
Gastrointestinal adverse events are the most consistently reported tolerability finding.
Controlled human evidenceEvent rates vary by population, regimen, duration, and analysis method. Long-term safety characterization remains incomplete.
Open sourceGastrointestinal adverse events are the most consistently reported tolerability finding.
Controlled human evidenceThe stated frequency is source-, product-, population-, route-, dose-, comparator-, and duration-specific; it is not a universal incidence estimate.
Open sourceNo source-qualified compound-specific warning or contraindication is encoded in the current record.
Evidence boundaryInvestigational; not approved by the FDA or any regulatory agency Long-term cardiovascular, renal, and rare-event safety; durability after discontinuation; and full peer-reviewed reporting from the pivotal obesity program.
The current record does not identify a reliable compound-specific pattern of events that caused study discontinuation.
Evidence boundaryThis is an evidence gap, not proof that discontinuations did not occur.
No compound-specific patient-facing urgent-action threshold is established in the current Relay record.
Evidence boundaryRelay does not infer emergency guidance from study discontinuations, mechanism, or incomplete adverse-event reporting.
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