Dosage — research context only
Retatrutide Dosage: What the Trials Studied
Phase 2 trials studied retatrutide at 1, 4, 8, and 12 mg once weekly. This page covers those study-design facts, the pharmacokinetics, and the important context: retatrutide is not approved, and no dose is a human recommendation.
Before the details
Retatrutide is an investigational drug — it has not been approved by any regulator and is not available as a prescription product. There is no approved dosing schedule. What this page documents is what doses were administered to participants in clinical trials, how the drug behaved in their bodies, and what outcomes those doses produced. That is study-design context, not guidance for anyone. Doses, half-life, injection schedule, and escalation patterns are described in the third person because they are facts about research protocols, not recommendations. If something on this page reads like a recommendation to take a specific amount, that is a mistake — this site does not and cannot provide medical advice. The full retatrutide trial record, including the safety findings that accompany these dose-level data, is on the Retatrutide research page.
Retatrutide dosage — Phase 2 obesity trial
In the 48-week Phase 2 obesity trial (Jastreboff AM, et al., NEJM, 2023), retatrutide was administered by subcutaneous injection once weekly at four fixed doses: 1 mg, 4 mg, 8 mg, and 12 mg [1]. Each arm used a gradual dose-escalation introduction — participants began at a lower starting amount and increased to the target level over the initial weeks — to manage gastrointestinal tolerance.
The dose-response relationship for body-weight reduction was clear: -8.7% (1 mg), -17.3% (4 mg), -22.8% (8 mg), and -24.2% (12 mg) versus -2.1% with placebo at 48 weeks [1]. Gastrointestinal adverse events, particularly nausea, were dose-dependent; the 12 mg group had the highest rate and the highest discontinuation rate (18%, primarily GI-driven).
Heart-rate increase was also dose-dependent, peaking around 24 weeks at approximately 5-7 bpm above baseline at the highest dose [1].
Retatrutide dosage — Phase 2 type 2 diabetes trial
The 36-week Phase 2 diabetes trial (Rosenstock J, et al., Lancet, 2023) used a more graduated scheme: doses of 0.5, 1.5, 3, and 3-to-12 mg once weekly with stepwise escalation [2]. The escalation design was intended to optimize GI tolerability in a diabetic population.
At 24 weeks: HbA1c reduction ranged from -0.79% (0.5 mg) to -2.02% (12 mg) versus -0.01% with placebo [2]. Body weight at 36 weeks ranged from -3.25% (0.5 mg) to -16.94% (12 mg) versus -3.00% with placebo. No severe hypoglycemia and no deaths were recorded; mild-to-moderate GI adverse events occurred in approximately 35% of participants at the highest dose [2].
Phase 1b pharmacokinetics — half-life and dose-response
The first-in-human Phase 1b study (Urva S, et al., Lancet, 2022) characterized the pharmacokinetics (how the drug distributes and clears from the body) that support once-weekly dosing [4].
Half-life: approximately 6 days in human plasma [4]. This 6-day half-life — compared with semaglutide's ~7 days or liraglutide's ~13 hours — is what makes weekly subcutaneous injection feasible. Steady-state plasma concentrations are reached within approximately 4 weeks of weekly dosing.
Dose escalation studied: 0.5, 1.5, 3, and 3/6/9/12 mg once weekly over 12 weeks [4]. The highest-dose group (reaching 12 mg with escalation) showed placebo-adjusted weight loss of -8.96 kg (90% CI -11.16 to -6.75 kg). Daily mean glucose fell by -2.8 mmol/L at 3 mg. Treatment-emergent adverse events occurred in 63% of participants, mostly GI and classified as mild or moderate.
The acylation of retatrutide's 39-amino-acid backbone with a C20 fatty-diacid chain binds the compound reversibly to albumin in plasma — a standard half-life extension strategy in this drug class that prevents rapid renal clearance and enables the extended dosing interval.
Retatrutide side effects — the clinical trial record
Across all completed Phase 1b and Phase 2 trials, the safety profile of retatrutide was consistent [1][2][4]:
Most common: nausea (up to 45% at 12 mg in the obesity trial), diarrhea, vomiting, constipation, and decreased appetite. All were dose-related and most were classified as mild or moderate [1].
Dose-dependent heart-rate increase: mean increases of approximately 5-7 bpm at the highest doses, peaking around 24 weeks [1]. The glucagon receptor component drives this via cAMP/PKA-mediated cardiac chronotropy.
Injection-site reactions: reported in approximately 8% of Phase 2 obesity trial participants [1].
Lean-mass reduction: Phase 2 body-composition data and a dedicated 2025 Lancet Diabetes & Endocrinology substudy confirmed absolute reductions in lean mass alongside fat mass, though the fat-to-lean ratio was more favorable than historic bariatric benchmarks.
No severe hypoglycemia was reported in the Phase 2 diabetes trial when background insulin doses were appropriately reduced [2]. Hypoglycemia risk exists when retatrutide is combined with insulin or sulfonylurea medications in the absence of dose adjustment.
How to take retatrutide: In clinical trials, retatrutide was administered by subcutaneous injection once weekly at a fixed scheduled time, using a supplied injection device. This is a description of the trial protocol. There is no approved instruction set for human use outside a clinical trial.
How often do participants receive retatrutide in trials? Once weekly. All completed trials used a once-weekly subcutaneous dosing interval, enabled by the ~6-day half-life [1][2][4].
Storage — clinical trial context
In clinical trials, retatrutide is supplied as a pre-formulated sterile product manufactured under Good Manufacturing Practice (GMP) conditions, stored and handled according to sponsor specifications — typically refrigerated before use. There is no approved consumer storage standard because there is no approved product.
How to store retatrutide: This question only applies to the trial investigational product, which is stored per sponsor protocol under controlled conditions. No equivalent guidance exists for research-labeled gray-market material, which has no verified composition, sterility, or stability data. This site does not provide storage instructions for such material.
How to mix retatrutide with bacteriostatic water: This question does not apply to retatrutide as studied in trials — the clinical trial preparation is pre-formulated and sterile, not a lyophilized powder requiring reconstitution. The mixing question arises because some research-labeled gray-market products are sold as lyophilized powders; this site does not provide reconstitution guidance for such products.