# Retatrutide Dosage: Trial Doses, Half-Life, and Pharmacokinetics > Retatrutide dosage data from Phase 1b and Phase 2 trials: doses of 1–12 mg once weekly studied, ~6-day half-life, subcutaneous route. Context from the published trial record, not medical guidance. Trial dose ranges, pharmacokinetic parameters, and route of administration as reported in the primary literature. ## The short version Retatrutide is an investigational drug studied by subcutaneous injection — meaning a shot under the skin — given once weekly. Clinical trials tested doses ranging from 0.5 mg to 12 mg, typically starting low and increasing over several weeks to reduce side effects. The drug stays in the body for roughly six days before half of it is cleared, which is why once-weekly dosing works. This page describes what doses were used in which trials and what pharmacokinetic properties the researchers measured. It is not a guide to self-administering retatrutide — the compound is not approved, and no standard formulation, reconstitution protocol, or storage condition exists outside the clinical-trial investigational product. The trial data on retatrutide dosage are summarized here as research context only. ## Retatrutide dosage Across the published clinical program, retatrutide has been studied at the following dose ranges: **Phase 1b (Urva et al., *Lancet* 2022):** Once-weekly subcutaneous doses of 0.5, 1.5, 3, 3/6, and 3/6/9/12 mg over 12 weeks in 72 adults with type 2 diabetes [4]. The stepped notation (e.g., 3/6/9/12) indicates progressive dose escalation — participants started at the lower value and stepped up through the sequence at scheduled intervals to manage tolerability. **Phase 2 obesity (Jastreboff et al., *N Engl J Med* 2023):** Once-weekly doses of 1, 4, 8, or 12 mg, or placebo, for 48 weeks in 338 adults with obesity [1]. No intermediate escalation between the fixed assigned doses was reported in the primary paper, though a gradual run-in was included. **Phase 2 type 2 diabetes (Rosenstock et al., *Lancet* 2023):** Stepwise dose escalation from 0.5 to 12 mg once weekly over 36 weeks in 281 adults with T2D [2]. These are study design facts — doses administered to specific trial populations under clinical oversight. They are not instructions for use. No approved formulation or indication exists. ## Half-life and pharmacokinetics **Half-life: approximately 6 days.** This parameter, established in the Phase 1b trial [4], is what enables once-weekly subcutaneous dosing. Retatrutide's extended half-life is engineered into its structure: the molecule is a 39-amino-acid peptide acylated (chemically attached) with a C20 fatty-diacid chain that promotes binding to albumin (the most abundant protein in blood plasma). Albumin binding extends circulation time substantially — from the hours a non-acylated peptide would persist to days, analogous to the mechanism used by related approved drugs in this class. Route of administration studied: subcutaneous injection, once weekly. No intravenous, intramuscular, or oral formulations have been studied in humans or reported in the published literature. **Absorption and distribution:** Subcutaneous injection delivers the compound into the hypodermis (the fatty layer beneath the skin), from which it is absorbed into systemic circulation. Albumin binding substantially extends the volume of distribution relative to an unmodified peptide. **Dose-response relationship:** The Phase 1b and Phase 2 data together establish a clear dose-response: both efficacy (weight loss, glycemic control) and the most common adverse events (GI events, heart-rate increase) scale with dose [1][2][4]. This relationship underlies the clinical trial convention of starting low and escalating to manage tolerability. ## How to reconstitute retatrutide There is no published or standardized reconstitution protocol for retatrutide. In clinical trials, the compound is provided as a clinical-trial investigational product by the sponsor under GMP (Good Manufacturing Practice) conditions, already formulated, qualified for sterility and endotoxin, and administered by trained clinical staff under a monitored protocol. Gray-market vials sold as research-labeled retatrutide are lyophilized (freeze-dried) powders. The reconstitution question commonly refers to these. Several points are relevant from a research-context perspective: - No analytical confirmation of identity or purity is available for gray-market material. - No stability data specific to retatrutide under research-vial conditions have been published. - The FDA has issued warning letters to vendors of research-labeled retatrutide citing FDCA violations [6]. This site does not provide reconstitution instructions and does not link to vendors. Any practical handling of a peptide in a research context requires identity confirmation by analytical methods (HPLC, MS), sterility and endotoxin testing, and appropriate physical containment — none of which gray-market supply chains provide. ## Retatrutide side effects Adverse events in the Phase 1b and Phase 2 trials were predominantly gastrointestinal. The full safety picture is documented on the [Retatrutide effects](/effects) page; the trial-documented adverse event profile is summarized here for pharmacological context. **Gastrointestinal:** Nausea, diarrhea, vomiting, and constipation were dose-dependent and occurred most frequently in the first weeks of treatment or following dose escalations. In the Phase 2 obesity trial, nausea affected up to 45% of participants at 12 mg; the 18% discontinuation rate at that dose was primarily GI-driven [1]. **Cardiovascular — heart rate:** A dose-dependent increase in resting heart rate was observed in Phase 2, peaking at approximately week 24 at 5–7 bpm above baseline at the highest doses. The mechanism is glucagon receptor-mediated: glucagon receptor activation increases cardiac chronotropy (the rate of the heart's contractile cycle) via cAMP/PKA intracellular signaling [1]. **Injection-site reactions:** Observed in approximately 8% of Phase 2 participants; mostly transient local reactions [1]. **No severe hypoglycemia** was reported in the Phase 2 obesity or Phase 2 T2D trials in the absence of background insulin or sulfonylurea therapy [1][2]. The combination of retatrutide with insulin or sulfonylureas carries a distinct hypoglycemia risk (see effects page). **Lean-mass reduction:** Phase 2 body-composition data confirmed reductions in lean body mass alongside fat mass, a finding common to the GLP-1-class but quantified specifically for retatrutide in a 2025 Lancet Diabetes & Endocrinology substudy [8]. ## Retatrutide cost Retatrutide has no commercial price because it is not an approved or commercially available drug. There is no retail price, no insurance pricing, and no compounding pharmacy cost — because there is no approved product. Gray-market research-labeled vials are sold at prices that vary widely by vendor; this site does not list, compare, or link to vendors. The FDA has issued warning letters to vendors of such material, and the products are unverified as to identity, purity, and concentration. When and if retatrutide receives regulatory approval, commercial pricing will be set by the developer and subject to payer negotiations. No public pricing commitment has been made. --- A cold-light reading of the investigational retatrutide trial record — Phase 1 through Phase 2 results logged to their primary sources, the long-term unknowns stated plainly, and no clinic, product, or prescription behind the page.