Retatrutide dosage: what the clinical trials studied.

Before the numbers

Retatrutide is investigational — it has not been approved by the FDA or any regulator. There is no approved dose, no labeled titration schedule, and no authorized prescription for this compound as of 2026. The figures on this page are study-design facts from published clinical trials: what doses were administered to which participants over what duration. They are reported here as documentation of the research record, not as dosing guidance.

The question "how much retatrutide per week" does not have an approved answer. What the Phase 2 trials studied, and how those study doses were structured, is what this page covers.

Retatrutide dosage: what Phase 1b and Phase 2 trials used

Phase 1b (LY3437943, first-in-human, 2022): Doses of 0.5, 1.5, 3, 3/6, and 3/6/9/12 mg were administered once weekly by subcutaneous injection (injection into the fatty layer beneath the skin) over 12 weeks to 72 adults with type 2 diabetes ^[4]. This was the trial that established the pharmacokinetic (PK — what the body does to the drug) and tolerability profile.

Phase 2 obesity trial (48 weeks, 2023): Participants were randomized to 1, 4, 8, or 12 mg once weekly subcutaneous for 48 weeks. Doses were escalated stepwise over the first several weeks at each arm to reduce GI adverse events ^[1].

Phase 2 type 2 diabetes trial (36 weeks, 2023): Doses ranged from 0.5 to 12 mg once weekly, administered with dose escalation starting at 0.5 mg ^[2].

All Phase 2 trials used once-weekly subcutaneous injection as the sole administration route. No oral, intravenous, or other routes have been studied in published trials.

Retatrutide half life

Retatrutide half life is approximately 6 days in human plasma, established in the Phase 1b pharmacokinetic analysis ^[4]. This extended half-life supports once-weekly dosing — meaning one subcutaneous injection per week maintains stable blood concentrations between doses.

The extended half-life is achieved through a C20 fatty-diacid modification on the peptide's structure. This modification allows retatrutide to bind to albumin — the most abundant protein in blood — which slows the rate at which the kidneys and liver clear it from circulation. Without this modification, a 39-amino-acid peptide would typically clear within hours.

For context: semaglutide has a half-life of approximately 7 days; tirzepatide approximately 5 days. Retatrutide's ~6-day half-life is within the same range, supporting the same once-weekly schedule studied for both.

How to reconstitute retatrutide

How to reconstitute retatrutide is a procedural question that applies only to research-labeled lyophilized (freeze-dried) material, which is neither approved nor verified. This site does not provide reconstitution, dilution, or preparation instructions for any form of retatrutide. The reason is direct: approved clinical-trial retatrutide is administered by trained staff in study sites using a formulation that is not available to the public. Research-labeled gray-market material of unverified identity and purity carries genuine injection safety risks regardless of how it is reconstituted.

The stability notes from the published research state that retatrutide has been studied only as a clinical-trial investigational product — no approved formulation, storage protocol, or reconstitution standard exists for any non-trial preparation.

How to mix retatrutide with bacteriostatic water: not documented in any published Phase 1 or Phase 2 trial; not a procedure this site addresses. How to take retatrutide: in clinical trials, it was administered by subcutaneous injection once weekly by study personnel. How to store retatrutide: trial material was handled under clinical trial conditions. No stability data for gray-market preparations have been published.

Retatrutide cost

Retatrutide cost is not a question that has a clear answer as of 2026 for two reasons. First, retatrutide is not an approved drug, so there is no list price, insurance coverage, or authorized pharmacy price. Second, gray-market research-labeled material circulates at varying prices from unregulated sources, but purchasing, possessing, or self-administering such material carries regulatory, safety, and legal risk and is not something this site facilitates or endorses.

For comparison, approved GLP-1 class drugs for obesity have list prices in the United States ranging from several hundred to over a thousand dollars per month before insurance, though patient programs and out-of-pocket costs vary widely. Retatrutide, if eventually approved, would be priced by Eli Lilly and subject to insurance negotiations — speculating on a price before Phase 3 results are published would not be meaningful.

Retatrutide availability

Retatrutide availability as an approved prescription drug: not available as of mid-2026. Phase 3 trials are ongoing. Regulatory review would follow Phase 3 completion.

When will retatrutide be available? The TRIUMPH Phase 3 program began enrolling in 2023–2024. Typical Phase 3 durations for obesity trials are 2–3 years of treatment plus analysis and regulatory submission. No projected approval date has been announced by Eli Lilly as of mid-2026. The 2025 systematic review of obesity drug pipeline trials identified retatrutide among 14 agents in active Phase 3 development, characterizing the incretin landscape as one of the most rapidly advancing areas in metabolic pharmacology ^[9].

Is retatrutide available through gray-market research channels? Material labeled as retatrutide is available from unregulated vendors, but it has no verified identity, purity, or sterility, and the FDA has issued warning letters citing violations for such sales. This site does not link to, recommend, or facilitate those channels.