# Retatrutide Dosage: Trial Doses, Half-Life, and Reconstitution Context > Retatrutide dosage in clinical trials: Phase 1b, Phase 2, and Phase 3 trial doses, ~6-day half-life, subcutaneous route, and why no approved dosing standard exists. The doses studied in Phase 1b, Phase 2 obesity, and Phase 2 diabetes trials. No approved dosing standard exists. No prescription guidance is given here. ## The short version Retatrutide has been studied at doses ranging from 0.5 mg to 12 mg once weekly by subcutaneous (under-the-skin) injection. Those are study-design facts from published clinical trials — not a recommended dose for any individual. Retatrutide is not an approved drug. There is no FDA label, no approved dose range, and no prescription standard. The half-life is approximately 6 days, which is why trials used once-weekly injections. This page summarizes what doses were used in which trials and what outcomes were observed at those doses. It does not give reconstitution instructions, titration schedules, or guidance on how to use retatrutide outside a clinical trial. ## Retatrutide dosage: trial-administered doses by program **Phase 1b — LY3437943 first-in-human (Urva et al., Lancet 2022):** Participants: 72 adults with type 2 diabetes. Duration: 12 weeks. Route: subcutaneous once weekly. Dose cohorts studied: 0.5 mg, 1.5 mg, 3 mg, 3/6 mg (stepwise escalation), and 3/6/9/12 mg (stepwise escalation) [4]. Key PK finding: half-life approximately 6 days, supporting once-weekly dosing. **Phase 2 obesity (Jastreboff et al., NEJM 2023):** Participants: 338 adults with obesity or overweight-plus-comorbidity. Duration: 48 weeks. Route: subcutaneous once weekly. Dose arms studied: 1 mg, 4 mg, 8 mg, 12 mg [1]. Weight outcomes by dose arm at 48 weeks: dose-dependent, largest effect at 12 mg (-24.2% mean body weight change vs -2.1% placebo). **Phase 2 type 2 diabetes (Rosenstock et al., Lancet 2023):** Participants: 281 adults with T2DM. Duration: 36 weeks. Route: subcutaneous once weekly. Dose range studied: 0.5 mg to 12 mg with stepwise escalation [2]. Glycemic and weight outcomes reported at 24 and 36 weeks. ## Half-life and pharmacokinetics Retatrutide's half-life in humans is approximately 6 days, as established in the Phase 1b PK trial (Urva et al., 2022) [4]. This is significantly longer than native GLP-1 (half-life: minutes) or GIP (half-life: minutes) because retatrutide is acylated with a C20 fatty-diacid chain that binds to albumin — the most abundant protein in blood — acting as a slow-release depot. The ~6-day half-life means: - Once-weekly subcutaneous dosing achieves stable plasma concentrations. - After stopping, the compound takes several weeks to clear. - Accumulation with weekly dosing reaches steady state around 4-5 weeks. Route studied: subcutaneous injection only. No oral, intranasal, or intravenous form has been studied in published clinical trials. ## How to reconstitute retatrutide This site does not provide reconstitution instructions for retatrutide obtained outside a clinical trial. In clinical trials, retatrutide was administered as a pre-formulated investigational drug product prepared under GMP (Good Manufacturing Practice) conditions by the trial sponsor and delivered to clinical sites in ready-to-use vials. Participants did not reconstitute the compound themselves. The stability note from the published data: retatrutide was studied only as a clinical-trial investigational product administered as a once-weekly subcutaneous injection. No approved formulation, storage standard, or reconstitution protocol exists for any non-trial preparation [dosage_research_context]. Gray-market research-labeled retatrutide powder would require reconstitution with bacteriostatic water or a similar sterile diluent before subcutaneous injection — but the identity, purity, and potency of such products cannot be verified, and the FDA has issued warning letters to vendors of such products. This site is a research digest; it does not instruct on preparation of unapproved injectable compounds. ## Dose-dependent outcomes: what the numbers show Across all Phase 2 arms, retatrutide's effects were clearly dose-dependent — larger doses produced larger effects, but also more adverse events. The following is a study-attributed summary: **Weight loss (Phase 2 obesity, 48 weeks) [1]:** - 1 mg: modest weight loss, not reported in detail - 4 mg: significant vs placebo - 8 mg: substantial vs placebo - 12 mg: -24.2% mean body weight change vs -2.1% placebo **GI adverse events:** dose-related frequency increase across all arms. Nausea up to 45% at highest dose [1]. **Heart-rate increase:** dose-dependent, peaking at week 24, approximately 5-7 bpm at highest doses [1]. A 2024 analysis summarized dose-dependent weight and metabolic effects (glycemia, lipids, blood pressure) across the entire Phase 2 retatrutide program [7]. --- Trial data on one investigational compound — published, cited, and held by no clinic and no vendor.