Retatrutide Dosage Guide: Chart, Schedule & Reconstitution

How retatrutide was dosed in the phase 2 trial

Retatrutide was administered once weekly by subcutaneous injection, with dosing continuing for 48 consecutive weeks in the phase 2 trial that produced its published dosing data. Researchers led by Ania Jastreboff of Yale School of Medicine, with co-author Kaplan of Harvard Medical School, randomized 338 adults (51.8% men) to one of six active-dose arms or placebo, publishing the results in the New England Journal of Medicine in 2023 (DOI: 10.1056/NEJMoa2301972).

The trial was double-blind, randomized and placebo-controlled, registered as ClinicalTrials.gov NCT04881760, with participants assigned across the 1 mg arm, two separate 4 mg arms, two separate 8 mg arms, the 12 mg arm and placebo. The two 4 mg arms shared the same eventual target but reached it from two different starting doses, and so did the two 8 mg arms: that pairing is what let researchers separate the effect of the starting dose from the effect of the target dose, the comparison the “why the starting dose matters” section below covers in detail. Every active arm was titrated: the weekly dose was stepped up every 4 weeks until each participant reached their assigned target, rather than starting at the full target dose on day one. Subcutaneous simply means injected under the skin, the same injection type used by approved GLP-1 medications such as semaglutide and tirzepatide, rather than into muscle or a vein. Retatrutide itself is a once-weekly triple-hormone-receptor agonist, acting on the GLP-1, GIP and glucagon receptors rather than on GLP-1 alone.

The weight-loss figures reported throughout this page are least-squares means, a statistical adjustment that accounts for small baseline differences between trial arms rather than a simple average of raw results. That is the standard reporting method for a randomized trial and the number the New England Journal of Medicine published, so it is the number reproduced here rather than an unadjusted average.

Because retatrutide remains investigational, there is no FDA-approved patient label and no official manufacturer dosing chart for it. Every number on this page traces back to the Jastreboff trial protocol, not to a prescribing guideline, and is provided so readers can understand what the published research actually measured.

The retatrutide dose escalation chart

The retatrutide dose escalation chart below reflects how the phase 2 trial moved each arm from its starting dose to its target dose in 4-week steps, not a recommendation for self-administration. Six active-dose arms were tested, and four of the six began below their eventual target.

Two starting doses were tested for both the 4 mg and 8 mg targets because the trial was designed to separate the starting dose’s effect on tolerability from the target dose’s effect on weight loss, the comparison the next section covers. All titration happened once weekly under clinical supervision for the full 48-week study; the schedule above is trial history, not a self-dosing guide.

Reading the table as a timeline rather than a single number helps explain why “retatrutide dosage” searches so often land on a range instead of one figure. The 12 mg arm spent its first 4 weeks at 2 mg, then moved to a higher weekly dose at each 4-week mark after that until reaching 12 mg, the longest escalation path the trial used. The 1 mg arm and the 4 mg (4 mg start) arm are the two exceptions in the table: both were assigned directly to their target with no step-up phase at all, because a target that low did not require gradual escalation under the trial protocol.

Why the starting dose matters more than the target dose

Retatrutide’s gastrointestinal side effects, nausea, diarrhea, vomiting and constipation, were dose-related and partially mitigated by starting at 2 mg rather than 4 mg, according to the phase 2 trial’s own safety findings. That single design choice, not the eventual target dose, is what made the higher-dose arms tolerable enough for participants to complete 48 weeks.

The practical read: two people can share the same 8 mg target and have very different early weeks. One started at 2 mg and spent 4 weeks adjusting before the first step-up; the other started at 4 mg and reached the same target through fewer, larger jumps. The trial links the slower on-ramp to milder gastrointestinal complaints, which is why three of the six active arms used a 2 mg starting dose instead of jumping straight to a higher number.

Heart rate was the other dose-dependent measure the trial tracked closely. Increases were dose-dependent and peaked at 24 weeks, then declined thereafter, meaning the cardiovascular signal did not simply keep climbing the longer someone stayed on the drug. For the full breakdown of what side effects were reported, and how often, see our retatrutide side effects guide.

Weight loss by retatrutide dose

Retatrutide produced dose-dependent weight loss in the phase 2 trial: the 12 mg arm reached a 24.2% mean reduction in body weight at 48 weeks, versus 2.1% on placebo. The table below reports the least-squares mean percentage change in body weight at 24 and 48 weeks for every dose the trial measured, placebo included.

The 4 mg and 8 mg rows above combine both starting-dose subgroups into a single figure for each target dose, since it is the target, not the starting dose, that drives the eventual weight-loss ceiling; the starting dose instead drives tolerability, which is what the previous section’s gastrointestinal-side-effect comparison covers.

Two patterns stand out. First, weight loss kept increasing at every dose between 24 and 48 weeks rather than leveling off: the 12 mg arm alone gained another 6.7 percentage points (17.5% to 24.2%) in the second half of the trial. Second, the jump from 1 mg to 4 mg (combined) at 48 weeks, 8.7% to 17.1%, an 8.4-point gain, dwarfs the jump from 8 mg to 12 mg, 22.8% to 24.2%, a 1.4-point gain, showing diminishing returns above the middle doses.

Reaching a weight-loss threshold, not just the average, is what most people searching this topic actually care about. At 48 weeks, 100% of participants on 8 mg or 12 mg had lost at least 5% of body weight, and 83% of the 12 mg group had lost 15% or more, the highest responder rate the trial reported.

The gap between 8 mg and 12 mg is widest at the hardest bar (75% versus 83% for 15%+ loss, an eight-point spread that is zero at the 5% bar), which is the responder-rate evidence behind the “is the extra dose worth it” question further down this page. Even the 4 mg group, the lowest dose in this responder analysis, comfortably separated from placebo at every threshold: 92% of it lost at least 5% of body weight against 27% on placebo, more than three times the placebo rate at the entry-level responder bar.

Reconstitution: how much bacteriostatic water

How much bacteriostatic water for 10 mg of retatrutide depends entirely on the concentration you’re solving for, since reconstitution is arithmetic, not a fixed rule: concentration in mg per mL equals the total milligrams in the vial divided by the milliliters of bacteriostatic water added. This section explains the math researchers and lab technicians use to describe a reconstituted vial; it is not an instruction to prepare or administer anything.

Take a 10 mg vial mixed with 1 mL of bacteriostatic water: the concentration works out to 10 mg divided by 1 mL, or 10 mg/mL. A 2 mg amount at that concentration is 2 mg divided by 10 mg/mL, which equals 0.2 mL, and on a U-100 insulin syringe (100 units per mL), 0.2 mL reads as 20 units. The same two-step math, concentration first, then volume to draw, applies to any vial size and any water volume.

The same arithmetic scales to larger vials. A 20 mg vial mixed with 2 mL of bacteriostatic water also yields 10 mg/mL (20 mg divided by 2 mL), so a 4 mg amount at that concentration is 4 mg divided by 10 mg/mL, or 0.4 mL, which is 40 units on a U-100 syringe. A 30 mg vial mixed with 3 mL likewise yields 10 mg/mL, so a 6 mg amount works out to 0.6 mL, or 60 units. Matching the water volume to the vial size this way keeps the resulting concentration the same across vial sizes, which is why 10 mg/mL shows up repeatedly in the table below.

Volume to draw is always the desired dose divided by the concentration in that row, and units on a U-100 syringe are that volume in mL multiplied by 100. Diluting further, adding more bacteriostatic water to the same vial, lowers the concentration and raises the volume needed for any given dose, which is why the 3 mL column above produces larger draw volumes than the 1 mL column for the same milligram amount: a lower concentration always means more liquid to measure the same dose, not less. For a live version of this arithmetic that does the division for you, use our retatrutide dosage calculator, built for exactly this math.

Storing reconstituted retatrutide

Because retatrutide has no FDA approval, there is no manufacturer storage label for a reconstituted vial, and any specific figure quoted online (a refrigeration temperature, a shelf-life in days) is not sourced from an approved product insert. Published handling guidance for reconstituted peptides in general points toward refrigeration rather than room temperature once bacteriostatic water has been added, because introducing water and a preservative to a lyophilized powder starts a slow degradation process that heat accelerates.

Does retatrutide need to be refrigerated? For a reconstituted, unapproved research peptide, the cautious and consistent answer drawn from handling guidance for comparable peptides is yes: refrigerated, protected from light, and used within the timeframe stated on the vial’s own documentation, since no clinical trial has published its own stability data for at-home storage. Before reconstitution, lyophilized (freeze-dried) peptide powder is comparatively stable and is typically kept refrigerated or frozen, per general peptide-handling literature.

General handling literature for reconstituted peptides also points to a few practices that are not specific to any single compound: mix by gently swirling or rolling the vial rather than shaking it, since vigorous agitation can physically damage a protein structure; keep the vial away from direct light, which is why amber or foil-wrapped packaging is common; and avoid repeated freeze-thaw cycles, each of which stresses the dissolved peptide more than a single, stable refrigeration period. A solution that has turned cloudy or changed color from its original appearance is a standard discard signal across peptide-handling guidance generally, not a retatrutide-specific finding.

None of this is dosing or handling instruction for a specific product. It explains the general chemistry and terminology behind the storage questions people search, because retatrutide itself carries no approved label to point to instead.

What you can actually be prescribed today

Retatrutide cannot legally be prescribed or bought for weight loss because it remains investigational, still moving through the clinical-trial process that produced every number on this page. Two other GLP-1-class medications, semaglutide and tirzepatide, are FDA-approved and available through licensed telehealth providers right now.

Both approved options use the same titrate-slowly principle discussed above for retatrutide: a clinician starts at a low dose and raises it over several weeks to manage gastrointestinal side effects, under real medical supervision rather than a self-directed schedule. Semaglutide and tirzepatide each carry an FDA-approved label with a defined starting dose, a defined titration interval and defined missed-dose guidance, the exact documentation retatrutide cannot have while it remains investigational. A licensed telehealth provider or in-person clinician evaluates eligibility, prescribes the approved medication, and adjusts the schedule based on how an individual tolerates each step, the same clinical oversight the retatrutide trial itself relied on.

Sources

Jastreboff AM, Kaplan LM, Frías JP, et al. “Triple-Hormone-Receptor Agonist Retatrutide for Obesity, A Phase 2 Trial.” New England Journal of Medicine, 2023;389(6):514–526. DOI: 10.1056/NEJMoa2301972. PMID 37366315. Registered as ClinicalTrials.gov NCT04881760. This is the primary source for every dosing and weight-loss figure on this page.

Rosenstock J, Frías J, et al. reported retatrutide’s effect in people with type 2 diabetes in a separate trial published in The Lancet in 2023. DOI: 10.1016/S0140-6736(23)01053-X.

Bajaj HS, et al. published newer retatrutide trial data in The Lancet on 13 June 2026. DOI: 10.1016/S0140-6736(26)00967-0, more recent than the sources most pages on this topic currently cite.