Retatrutide

What it is

Retatrutide is a lab-made peptide built on a GIP-hormone backbone with a fatty acid chain attached, which lets it cling to albumin in the blood so it lasts about a week instead of minutes - the same trick semaglutide uses. What makes it different is that it does not just copy one gut hormone, it activates three receptors at once: GLP-1, GIP, and glucagon. The GLP-1 activity quiets appetite, slows stomach emptying, and boosts insulin release. The GIP activity adds extra appetite suppression on top of that and appears to blunt some of the nausea GLP-1 alone tends to cause. The glucagon receptor is the unusual third piece: instead of raising blood sugar the way glucagon normally does on its own, in this three-way combination it appears to raise energy expenditure and push the liver to burn fat rather than store it. Activating all three at once is the reason Eli Lilly's Phase 2 obesity trial saw weight loss well beyond what earlier single- or dual-receptor drugs produced. It remains investigational - not approved anywhere in the world - and is currently working through Phase 3 trials for obesity, type 2 diabetes, sleep apnea, and knee osteoarthritis.

Dose ranges

Study-backed ranges carry a source you can open. Community ranges are widely reported but not clinically established - treat them as what people do, not as advice.

Reconstitution & storage

Retatrutide is investigational - there is no FDA-approved product and therefore no official vial size or reconstitution instructions. These figures come from peptide-vendor and community guides only. Common charts list 5-10 mg vials mixed with 1-3 mL bacteriostatic water (roughly 2.5-10 mg/mL), and some vendors sell larger 15-30 mg (occasionally 60 mg) vials to match the higher weekly doses used in trials, mixed with proportionally more BAC water. Let the vial reach room temperature, inject the bacteriostatic water slowly down the inside wall rather than directly onto the powder, and swirl gently rather than shaking. Use bacteriostatic water made for injection, never plain or sterile water. Because no legitimate manufacturer sells retatrutide for human use, anything labeled as a research vial is unregulated and its actual contents and purity cannot be verified.

Common stacks

Interactions & cautions

Retatrutide is investigational, so there is no FDA label and no official drug-interaction list. What follows comes from its own trial protocol and published safety data, plus the pattern it shares with other GLP-1/GIP medicines. The sponsor's Phase 2 protocol lists 'safety topics of special interest' carried over from other GLP-1 and GIP/GLP-1 receptor agonist programs - pancreatic safety, cardiovascular events, hypoglycemia, hypersensitivity reactions, and thyroid C-cell effects - while noting that most of these had not actually been observed with retatrutide at that stage of development. That same protocol excludes anyone with a personal or family history of medullary thyroid carcinoma or MEN2, an elevated screening calcitonin level, a history of acute or chronic pancreatitis, significant gastroparesis or other conditions/drugs that slow gastric emptying, or an eGFR under 45 mL/min/1.73m2. Because retatrutide, like other GLP-1 drugs, slows stomach emptying, it can plausibly change how fast oral medications are absorbed, which is part of why the trial excluded people already on drugs that directly affect GI motility. Dose-dependent increases in heart rate and decreases in blood pressure showed up consistently across the Phase 1 and Phase 2 studies, generally easing over time. A 2026 review also flags a caution specific to triple agonists: the glucagon-receptor component increases protein breakdown, so its long-term effect on muscle mass, especially in anyone already at risk of sarcopenia, is not yet fully worked out. Long-term cardiovascular and kidney outcome data are still pending, so that same review suggests people with existing cardiovascular or kidney disease may currently be better served by a GLP-1 drug that already has established outcome data, such as semaglutide.

Questions people ask

Sources

1. [1]Triple-Hormone-Receptor Agonist Retatrutide for Obesity - A Phase 2 Trial PMID 37366315studyConfirms the Phase 2 obesity trial dose arms (1, 4, 8, 12 mg weekly with escalation), 48-week weight-loss results by arm, and that gastrointestinal adverse events were the most common, dose-related effect.
2. [2]A Phase 2 Study of Once-Weekly LY3437943 Compared With Placebo in Participants Who Have Obesity or Are Overweight With Weight-Related Comorbidities (NCT04881760)trial_registryOfficial registry record confirming trial arms/doses, the stepwise titration schedule through week 12, Eli Lilly as sponsor, 338-participant enrollment, and completed status.
3. [3]LY3437943, a novel triple GIP, GLP-1, and glucagon receptor agonist in people with type 2 diabetes: a phase 1b, multicentre, double-blind, placebo-controlled, randomised, multiple-ascending dose trial PMID 36354040studyReports an approximately 6-day, dose-proportional half-life; the 0.5/1.5/3 mg fixed-dose and 3-to-6 mg / 3-to-12 mg titrated cohorts; and gastrointestinal and heart-rate adverse effects.
4. [4]LY3437943, a novel triple glucagon, GIP, and GLP-1 receptor agonist for glycemic control and weight loss: From discovery to clinical proof of concept PMID 35985340studyDescribes the discovery and preclinical pharmacology of LY3437943 as a triple GCGR/GIPR/GLP-1R agonist and early clinical pharmacokinetics supporting once-weekly dosing.
5. [5]A Study of LY3437943 in Participants Who Have Obesity or Are Overweight - Clinical Trial Protocol (Study J1I-MC-GZBF / NCT04881760)trial_protocolThe sponsor's own protocol document: reports a 5-7 day mean terminal half-life from the first-in-human single-ascending-dose study (GZBA), the Phase 1b multiple-ascending-dose cohort structure (GZBB), and exclusion criteria covering personal/family history of medullary thyroid carcinoma or MEN2, elevated calcitonin, pancreatitis history, gastroparesis, and renal impairment (eGFR under 45).
6. [6]What is the mechanism of action of retatrutide? - Lilly MedicalmanufacturerEli Lilly's own medical information page confirms retatrutide is 'an investigational molecule and is not currently approved in any countries or geographies,' describes its mechanism as a GIP/GLP-1/glucagon receptor agonist, states an approximately 6-day half-life with peak concentration at 12-72 hours, and reports 8.9-fold greater potency at the GIP receptor than natural GIP.
7. [7]Triple Agonism Based Therapies for ObesityreviewBreaks down how each receptor (GLP-1, GIP, glucagon) contributes to retatrutide's effect, reports Phase 2 safety data (about 4% serious-adverse-event rate, 6-16% discontinuation across arms), and flags an open caution about the glucagon component's effect on lean mass plus pending long-term cardiovascular outcome data.
8. [8]How to Reconstitute Retatrutide Research Peptide: Easy Step-by-Step for LabscommunityVendor reconstitution guide giving 5 mg and 10 mg vial examples mixed with 1-3 mL bacteriostatic water, plus technique notes (slow wall injection, gentle swirl, refrigerate, never freeze reconstituted solution).
9. [9]Retatrutide (GLP-3) Reconstitution + Free CalculatorcommunityCommunity reconstitution chart covering 5-60 mg vial sizes with matching bacteriostatic water volumes and concentrations, and reports 28-60 days of refrigerated stability once mixed.
10. [10]Retatrutide Storage Guide: Refrigeration & HandlingcommunityCommunity storage guidance: lyophilized powder at 2-8C short-term or -20C (some sources say -80C) for longer archival; reconstituted solution at 2-8C, never frozen, with freeze-thaw cycling flagged as damaging.
11. [11]Retatrutide Reddit Summary: Community Reports vs Phase 2 EvidencecommunitySummarizes Reddit-reported self-dosing between 2 and 12 mg weekly, starting doses clustered around 2 mg, and titration paces typically faster and less structured than the clinical trial protocol.