DOSING RECORD — Study Design Filed
Retatrutide Dosage: What Phase 1 and Phase 2 Trials Actually Studied
Trial doses, pharmacokinetics, and escalation protocols — documented as study-design facts. Retatrutide is investigational and not approved for human use outside clinical trials.
Before the numbers — what this page reports
Retatrutide (LY3437943) is an investigational drug — not approved by the FDA or any regulator. The doses listed on this page are what Eli Lilly's clinical trials administered to study participants. They are published data, reported here as study-design facts for anyone following the trial literature. They are not recommendations, instructions, or suggested dosing for any purpose. The trial doses tell us what was studied and at what level side effects were manageable under clinical oversight; they say nothing about what is safe or appropriate outside that setting. Retatrutide is not commercially available as a prescription drug. This page exists to document what the studies measured — not to guide use.
Retatrutide dosage — what the trials studied
All retatrutide dosing in human trials has been administered as a once-weekly subcutaneous injection (injected into the fat layer under the skin). No other route has been studied in humans.
Phase 1b (first-in-human, 2022): Doses of 0.5, 1.5, 3 mg, and escalating sequences (3/6 mg; 3/6/9/12 mg) once weekly over 12 weeks in adults with type 2 diabetes [4]. This trial established the pharmacokinetics — how the drug behaves in the body.
Phase 2 obesity trial (2023): Doses of 1, 4, 8, and 12 mg once weekly over 48 weeks, using a gradual dose-escalation protocol to manage GI side effects [1]. The 12 mg arm showed -24.2% mean body-weight change at 48 weeks.
Phase 2 type 2 diabetes trial (2023): Step-wise escalation from 0.5 mg up to 12 mg once weekly over 36 weeks [2]. At 12 mg: HbA1c -2.02% at 24 weeks; body weight -16.94% at 36 weeks.
Phase 3 TRIUMPH program: Once-weekly subcutaneous at Phase 3 dosing — specific doses not yet publicly detailed in trial design papers. Results pending.
Half-life and pharmacokinetics
Retatrutide has an approximately 6-day half-life in human plasma, established in the Phase 1b trial [4]. Half-life (the time for blood concentration to fall by half) of ~6 days is what makes once-weekly dosing pharmacologically rational — the drug maintains steady blood levels between weekly injections without daily administration. The C20 fatty-diacid acylation on retatrutide's backbone binds albumin (the most abundant protein in blood plasma), which substantially extends the time the molecule stays in circulation compared to an unmodified peptide. Molecular weight is 4731.33 Da; molecular formula C221H342N46O68. CAS number 2381089-83-2. PubChem CID (sodium salt form) 171934787.
How to reconstitute retatrutide
This is a question the published clinical trial record does not answer for non-trial settings — and intentionally so. Clinical trials use pre-formulated, sterility-tested, endotoxin-assayed vials prepared under Good Manufacturing Practice conditions by Eli Lilly. There is no approved or validated reconstitution standard for any commercial, compounded, or research-labeled retatrutide preparation, because there is no approved retatrutide product. Gray-market research-labeled vials are unregulated, of unverified identity and purity, and have no standardized handling instructions. The FDA's position — reflected in the 50+ warning letters issued in 2025 — is that such material violates the FD&C Act. This site does not provide reconstitution instructions. The question is documented here because it is frequently searched; the honest answer is that the trial literature provides no validated protocol applicable outside a clinical setting.
Dose-escalation and tolerability
All Phase 2 trials used structured dose-escalation protocols — starting at low doses and stepping up over weeks — specifically to manage GI adverse events (nausea, diarrhea, vomiting, constipation) that are dose-dependent with GLP-1/GIP receptor agonism [1][2]. In the Phase 2 obesity trial, discontinuation due to adverse events was 18% at the 12 mg dose, with GI events as the principal reason. In the type 2 diabetes trial, GI AEs occurred in approximately 35% of participants; no severe hypoglycemia was recorded in participants not on background insulin or sulfonylureas. The heart-rate increase (approximately 5-7 bpm at highest doses) was dose-dependent and peaked around 24 weeks in the obesity trial [1]. Long-term cardiovascular implications are under study in the dedicated outcomes trial.
Retatrutide cost
Retatrutide has no commercial price because it is not approved for sale anywhere. Clinical trial participants receive it at no cost as part of the trial protocol. Gray-market research-labeled material is available at varying prices through unregulated vendors, but such sources are unverified for identity, purity, and concentration, and the FDA has taken enforcement action against vendors of this material. No cost comparison to approved compounds is meaningful at this stage of development. When and if retatrutide reaches regulatory approval, pricing will be determined by the manufacturer and healthcare system. This site does not provide pricing guidance and does not link to commercial sources.