Retatrutide is the first triple GLP-1/GIP/glucagon receptor agonist to reach large-scale clinical trials, with a plasma half-life of ~6 days enabling once-weekly dosing. Phase 2 data showed 24.2% mean body weight loss at 48 weeks — a record for any obesity pharmacotherapy at time of publication.[1]
Retatrutide: Halflife Labs records ~144h (6 days) for SC. Evidence classification: Published human or clinical source. Source summary: Jastreboff et al., NEJM 2023.
Limitation: This is a population-level source statement, not a measured concentration or individualized prediction. Scientific review is documented on this page; the limited reviewer scope is defined on the About page.
Stable record ID: hlc:retatrutide · Page revision: 2026-06-11 · Open the primary source
Retatrutide is an investigational triple agonist studied at the GIP, GLP-1, and glucagon receptors. Published clinical research supports an approximately six-day half-life estimate and once-weekly study administration. As of June 11, 2026, Lilly reports Phase 3 TRIUMPH results and ongoing trials; FDA approval is not established by the primary sources reviewed here.
| Statement | Classification | Source basis |
|---|---|---|
| Retatrutide is a GIP/GLP-1/glucagon receptor agonist | Known | Published Phase 2 trial and sponsor trial materials |
| Half-life is approximately six days | Clinical estimate | Population-level clinical research |
| Phase 3 results have been reported | Known sponsor-reported status | Lilly 2026 investor release and trial registry |
| FDA-approved commercial availability | Not established | No approval source identified in this review |
| Exact individual concentration or response | Unknown | Cannot be derived from a consumer dose log |
The peer-reviewed Phase 2 trial is the strongest published foundation for efficacy and safety statements on this page. Sponsor-reported Phase 3 results are current and relevant, but an investor release is not a substitute for a complete peer-reviewed report or an FDA approval decision. Each claim should retain its source type and date.
Using an approximately six-day half-life, five half-lives is about 30 days. That is a simplified estimate for substantial elimination after the last event. Repeated weekly administration produces accumulation in a model, but exact peak, trough, and washout values vary and require more than a generic half-life input.
Long-term post-approval safety, final labeling, approved indications, commercial timing, and product-specific instructions remain unknown until authoritative sources establish them. A model should not be used to imitate a treatment plan for an investigational drug.
Retatrutide's GLP-1R component functions identically to semaglutide and tirzepatide: it drives glucose-dependent insulin secretion from pancreatic beta cells, delays gastric emptying to reduce post-meal glucose excursions, and activates hypothalamic circuits that suppress appetite and reduce caloric intake. The structural basis for retatrutide's extended half-life is a C18 fatty di-acid side chain — the same albumin-binding architecture used in semaglutide — which creates a depot effect after subcutaneous injection and slows renal clearance, achieving a plasma half-life of approximately 6 days (144 hours) based on Phase 2 human PK data.[1] This extended half-life supports once-weekly dosing without the need for depot formulation technologies.
Retatrutide's GIPR agonism is described as "full agonism" — similar in magnitude to tirzepatide, which established the dual GLP-1R/GIPR class. GIP receptor activation potentiates glucose-stimulated insulin secretion through a cAMP-dependent pathway distinct from GLP-1R signaling, providing additive insulinotropic effects that do not appear to substantially increase hypoglycemia risk. At the adipocyte level, GIPR activation may enhance intracellular lipid mobilization and fatty acid oxidation, contributing to the superior weight loss seen with dual and triple agonists compared to GLP-1 monotherapy. The combination of GLP-1R and GIPR agonism in retatrutide appears to produce synergistic weight loss beyond what either mechanism achieves alone, as seen in preclinical models and reflected in the Phase 2 efficacy results.[1]
The glucagon receptor (GCGR) component is what sets retatrutide apart from semaglutide and tirzepatide. In the liver, glucagon receptor activation increases hepatic energy expenditure by upregulating fatty acid beta-oxidation, reduces de novo lipogenesis, and promotes export of triglycerides — collectively reducing hepatic steatosis and improving markers of metabolic dysfunction-associated steatohepatitis (MASH). At the whole-body level, GCGR agonism increases basal metabolic rate beyond what is achieved by caloric restriction alone, creating a caloric deficit that adds to the appetite-suppressive effects of GLP-1R agonism. A theoretical concern is that glucagon normally raises blood glucose; however, in the triple-agonist context the GLP-1R component dominates glucose control, suppressing the hyperglycemic counterregulatory effect. Phase 2 data confirmed that fasting glucose was well-controlled at all retatrutide doses, validating this mechanistic rationale.[1]
The Halflife app plots your continuously updated estimated plasma-remaining curve — see the model's estimate of when your dose peaks, troughs, and clears. All on-device, no account required.
Download on App StoreUnderstanding retatrutide's pharmacokinetics requires thinking in three nested timeframes that each have distinct clinical relevance:
The following table assumes a single terminal dose. Each row represents one additional half-life (~6 days) of clearance. At 5 half-lives (~30 days), plasma concentration is below 3% of peak — considered clinically negligible.
| Days After Last Dose | Half-Lives Elapsed | Approximate % Remaining | Clinical Note |
|---|---|---|---|
| 6 days | 1 | ~50% | Next scheduled dose window; full GI effects persist |
| 12 days | 2 | ~25% | Partial activity; appetite suppression still present |
| 18 days | 3 | ~12.5% | Reduced efficacy; GI side effects mostly resolved |
| 24 days | 4 | ~6% | Clinically sub-therapeutic; weight regain may begin |
| 30 days | 5 | ~3% | Effectively cleared — standard washout period |
| Route | Available | Human Data | Notes |
|---|---|---|---|
| SC injection (weekly) | Yes | Phase 2 RCT | Established route; all Phase 3 trials use SC weekly |
| IV | Investigational | Limited | Used in early PK studies only; not a clinical route |
| IM | No | None | No published data; not under investigation |
| Oral | No | None | No oral formulation in development; SC remains the only route |
Retatrutide sits within the GLP-1 agonist class but occupies a distinct mechanistic niche due to GCGR co-agonism. The table below compares pharmacokinetically similar compounds:
| Compound | Receptor Targets | Half-Life | FDA Status | Route |
|---|---|---|---|---|
| Retatrutide (LY3437943) | GLP-1 / GIP / GCG triple | ~6 days | Phase 3 (not approved) | SC weekly |
| Tirzepatide | GLP-1 / GIP dual | ~5 days | FDA approved (Mounjaro/Zepbound) | SC weekly |
| Semaglutide | GLP-1 only | ~7 days | FDA approved (Ozempic/Wegovy) | SC weekly / oral |
| Cagrilintide | Amylin analogue | ~7 days | Phase 3 (with semaglutide) | SC weekly |
The landmark Phase 2 trial by Jastreboff et al. enrolled 338 adults with obesity (BMI ≥27 kg/m²) without diabetes and randomized them to retatrutide or placebo for 48 weeks.[1] Key findings by dose group at Week 48:
| Dose (SC weekly) | Mean % Weight Loss | % Achieving ≥10% Loss | % Achieving ≥15% Loss |
|---|---|---|---|
| Placebo | ~2.1% | 16% | 5% |
| 1 mg | ~8.7% | 45% | 27% |
| 4 mg | ~17.3% | 82% | 64% |
| 8 mg | ~22.8% | 92% | 83% |
| 12 mg (max tested) | ~24.2% | — | ~90% |
Figures are approximate from the published Phase 2 obesity trial (PMID 37366315). The maximum tested dose was 12 mg weekly. Complete peer-reviewed Phase 3 reporting, any FDA decision, and final product labeling remain pending or unknown from the sources reviewed here.
| Parameter | Source | Evidence Level |
|---|---|---|
| Half-life, Tmax, PK parameters | Jastreboff AM et al. NEJM 2023 (PMID 37366315) | Human PK Study — Phase 2 RCT |
| Protein binding / albumin mechanism | Structural analogy to semaglutide (C18 fatty acid); class inference | Mechanistic extrapolation |
| FDA status / Phase 3 | ClinicalTrials.gov; Eli Lilly public disclosures | Regulatory / sponsor communication |
The most common adverse events observed in Phase 2 were gastrointestinal in nature — nausea (up to 42%), vomiting, and diarrhea — consistent with the GLP-1 drug class. These events were dose-dependent and typically peaked during dose escalation, then attenuated with continued use. At higher doses (≥8 mg), GI burden appeared more pronounced than historically reported for semaglutide 2.4 mg, though cross-trial comparisons should be interpreted cautiously.[1]
A modest, dose-dependent elevation in resting pulse rate was noted across retatrutide groups in Phase 2, consistent with effects observed with other GLP-1 and dual agonists. The clinical significance of this finding at the Phase 3 scale and in patients with pre-existing cardiovascular disease is under evaluation. Retatrutide is investigational — do not use outside clinical trial settings and consult a physician before considering any GLP-1 class agent.
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