What the trials administered — and what no trial can authorize outside a clinic.

The brief version

This page documents the dose figures from published retatrutide clinical trials. It is not dosing guidance — retatrutide is an investigational compound, not an approved drug, and no prescription exists for it outside clinical trial enrollment.

The trials studied doses of 1, 4, 8, and 12 mg, given as subcutaneous (under-the-skin) injections once a week. The compound has a half-life of approximately 6 days, which is why once-weekly dosing works — it stays in the bloodstream long enough to maintain effect between injections. The highest dose studied (12 mg) produced the largest weight and liver-fat reductions in Phase 2.

People asking about reconstitution or mixing are asking about gray-market research vials — a context entirely outside clinical oversight, with no verified purity, no approved storage standard, and no pharmaceutical-grade formulation. That context is addressed in this page's section on the subject.

Retatrutide dosage

Phase 1b (first-in-human, Lancet 2022 ^[4]): Escalating subcutaneous doses of 0.5, 1.5, 3, 3/6, and 3/6/9/12 mg once weekly over 12 weeks in 72 adults with type 2 diabetes. This study established the pharmacokinetic profile and safety baseline for the compound.

Phase 2 obesity (NEJM 2023 ^[1]): 1 mg, 4 mg, 8 mg, and 12 mg subcutaneous once weekly over 48 weeks. Weight loss was dose-dependent across all four arms.

Phase 2 type 2 diabetes (Lancet 2023 ^[2]): 0.5–12 mg once weekly with stepwise escalation over 36 weeks, with most patients reaching 12 mg by the final weeks of the study.

Phase 2a MASLD substudy (Nature Medicine 2024 ^[5]): 1 mg, 4 mg, 8 mg, and 12 mg once weekly, 48 weeks, in participants with at least 10% liver fat.

All dose figures above are study-design facts drawn from published trial protocols. They are not a prescription, a protocol, or a recommendation for any use outside those trials.

Retatrutide half life

The Phase 1b study established a plasma half-life of approximately 6 days for retatrutide ^[4]. This extended half-life is engineered into the molecule's design: retatrutide is a 39-amino-acid peptide acylated with a C20 fatty-diacid chain that allows it to bind reversibly to albumin (the most abundant protein in blood plasma). Albumin binding acts as a depot, slowly releasing the free peptide over time and substantially extending circulation relative to unmodified GLP-1 analogs.

The ~6-day half-life means steady-state plasma concentrations are reached after approximately 4–5 doses under weekly dosing, and the compound clears over several weeks after discontinuation. This pharmacokinetic profile was specifically engineered to match the once-weekly convenience of the Phase 2/3 trial schedule.

How to reconstitute retatrutide

This question applies to research-labeled peptide vials sold through gray-market channels — not to any approved pharmaceutical product, which does not yet exist.

Retatrutide is studied only as a clinical-trial investigational product administered by trained clinical-trial staff. There is no approved formulation, storage standard, or reconstitution protocol for any non-trial preparation. Clinical trial vials are not available outside enrollment, and the investigational drug product used in TRIUMPH trials is not the same as unregulated peptide vials.

For gray-market research vials: peptide manufacturers conventionally supply lyophilized (freeze-dried) powder reconstituted with bacteriostatic water for injection (water preserved with benzyl alcohol to inhibit microbial growth), but this represents a general peptide chemistry convention, not an approved or authorized procedure for retatrutide specifically. No stability data, endotoxin limits, or sterility specifications exist in the public domain for non-trial retatrutide preparations. The FDA cited gray-market retatrutide vendors more than 50 times in 2025 for FD&C Act violations.

This section documents the question as it appears in search data; it does not authorize, instruct, or endorse any reconstitution of unapproved retatrutide outside a clinical trial.

Retatrutide side effects

The following adverse events are drawn from published Phase 2 trial data — not community reports.

Gastrointestinal: Nausea was the most common adverse event, affecting up to 45% of participants at 12 mg in the obesity trial. Vomiting, diarrhea, and constipation were also dose-related ^[1]. GI adverse events drove the 18% discontinuation rate at the highest dose.

Heart rate: Dose-dependent heart-rate increase, mean approximately 5–7 bpm at highest doses, peaking around week 24. The glucagon receptor arm drives this effect via cAMP/PKA cardiac signaling ^[1].

Hypoglycemia: No severe hypoglycemia was observed in the Phase 2 obesity trial (non-diabetic population). In the type 2 diabetes trial, participants on insulin required dose-reduction to avoid hypoglycemia ^[2].

Injection site reactions: Documented in approximately 8% of Phase 2 participants.

Lean mass loss: The body-composition substudy confirmed absolute lean-mass reduction alongside fat-mass reduction in the type 2 diabetes trial population.

See Retatrutide effects for the community-report layer and full safety cautions.

Retatrutide cost

No approved commercial product exists, so no approved pricing exists. Eli Lilly has not announced list pricing for retatrutide; any such announcement would follow FDA approval, which has not occurred.

Gray-market research vials are sold at widely varying prices through unregulated peptide vendors, but those prices are not relevant to what an approved drug would cost — they reflect an unregulated supply chain selling unverified material, not a pharmaceutical pricing decision.

For reference, approved GLP-1 class agents in the obesity indication have had US list prices in the range of $900–$1,400 per month before insurer negotiation and manufacturer discounts; retatrutide's pricing, should it reach approval, would be set by Eli Lilly and negotiated with payers independently. No published guidance exists.