Retatrutide Dosage Calculator
Retatrutide is an investigational once-weekly injection that acts on GLP-1, GIP and glucagon receptors. It is the peptide people most often ask reconstitution questions about, because it ships as a dry powder in vial sizes from 5 mg to 60 mg and every vial size changes the math.
This page does the arithmetic for a retatrutide vial: how much bacteriostatic water gives you a sensible concentration, and how many units on an insulin syringe equal the milligram dose you were given.
Clinical trialDoses come from registered human trials, but no approved product or label exists. · Reviewed by the FormBlends Editorial Standards Team · 2026-09-03
Clinical trialPhase 2 tested 1, 4, 8 and 12 mg once weekly, started at 2 or 4 mg. No approved product or label exists.
Draw to
40 units
0.4 mL
Volume
0.4 mL
1 unit = 0.01 mL on a U-100 syringe
Concentration
5 mg/mL
50 mcg in every unit
Doses per vial
5
about 5 days at this frequency
This draw also fits a 0.5 mL syringe, which has finer marks and is easier to read at this volume.
How much water should I use for this dose?
Volumes that put your dose on a printed mark of the 1 mL syringe, inside the accurate part of the barrel.
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FDA compounding status (2026-09-01): Not eligible. FDA states retatrutide and cagrilintide cannot be used in compounding under federal law; investigational, not a component of any approved drug. Full status table and sources
What the Retatrutide dose evidence actually is
Phase 2 tested 1, 4, 8 and 12 mg once weekly, started at 2 or 4 mg. No approved product or label exists.
The only human dosing data come from registered trials. The phase 2 study published in the New England Journal of Medicine in 2023 randomised adults with obesity to 1 mg, 4 mg, 8 mg or 12 mg once weekly for 48 weeks, with the higher arms started at 2 mg or 4 mg and stepped up over several weeks. Phase 3 programs have used maintenance doses in the same range.
Retatrutide is not an approved drug. FDA has said it is not eligible for compounding, so there is no pharmacy label to follow either. Treat any dose you were given as the number to enter here, and treat the trial figures as context, not instruction.
Retatrutide units at each water volume
The table uses a 10 mg vial. Each cell is the draw on a U-100 insulin syringe for that dose at that water volume. Cells above 100 units do not fit a 1 mL syringe; cells below 10 units sit in the part of a 1 mL barrel where measurement error rises, and a 0.5 mL or 0.3 mL syringe reads them better.
| Dose | 10 mg + 1 mL10 mg/mL | 10 mg + 2 mL5 mg/mL | 10 mg + 3 mL3.333 mg/mL | 10 mg + 5 mL2 mg/mL |
|---|---|---|---|---|
| 2 mg | 20 units | 40 units | 60 units | 100 units |
| 4 mg | 40 units | 80 units | 120 (does not fit) | 200 (does not fit) |
| 8 mg | 80 units | 160 (does not fit) | 240 (does not fit) | 400 (does not fit) |
Worked example: 10 mg with 2 mL is 5 mg per mL, so 2 mg (2 mg, the lowest starting dose used in the phase 2 trial) is 40 units, or 0.4 mL.
Mixing Retatrutide
A 10 mg vial mixed with 2 mL gives 5 mg per mL, so 2 mg is 40 units on a U-100 syringe. The same 10 mg vial mixed with 1 mL gives 10 mg per mL and the same 2 mg dose becomes 20 units.
Large vials are where people get stuck. A 30 mg or 60 mg vial mixed to 10 mg per mL needs 3 mL or 6 mL of water, and many research vials do not hold 6 mL. If your vial cannot take the volume you want, use a stronger concentration and accept a smaller draw. Plan the volume before you open the water.
The trap to avoid is the one-to-one rule. Ten units equals one milligram only when the concentration is exactly 10 mg per mL. Change the water and the rule breaks.
Storing Retatrutide after mixing
Keep the dry powder refrigerated until you mix it. After mixing with bacteriostatic water, keep the vial at 2 to 8 degrees Celsius and treat 28 days after the first puncture as the ceiling, which is the USP multiple-dose container rule, not a potency guarantee.
Retatrutide calculator questions
How much bacteriostatic water for 10 mg of retatrutide?
There is no single correct volume. Two millilitres gives 5 mg per mL, so a 2 mg dose is 40 units and a 4 mg dose is 80 units. One millilitre gives 10 mg per mL, so those doses become 20 and 40 units. Pick the volume that puts your dose between about 10 and 40 units on the syringe you own.
How many units is 2 mg of retatrutide?
It depends entirely on the concentration. At 5 mg per mL it is 40 units. At 10 mg per mL it is 20 units. At 20 mg per mL it is 10 units. Enter your vial size and water volume above and the calculator gives the exact number for your vial.
How much bac water for 30 mg retatrutide?
Three millilitres gives 10 mg per mL, which keeps the arithmetic simple: 10 units per milligram. Two millilitres gives 15 mg per mL, which fits a smaller vial but makes each unit worth 150 mcg. The calculator's water recommendation shows which volumes land your dose on a printed tick mark.
What was the retatrutide starting dose in trials?
In the phase 2 trial, the 4 mg and 8 mg arms started at 2 mg and the 12 mg arm started at 2 mg or 4 mg, then escalated every four weeks. Those are trial protocols for an investigational drug, not a label.
Sources
Retatrutide guide
Evidence, mechanism, side effects and regulatory status.
The full peptide calculator
All peptides, pre-mixed vials, blends, mistakes and concentration changes.
Free downloads built from this calculator's math
Peptide Dosing and Reconstitution Chart 2026
20 pages, 12 peptides, every vial size, units at five water volumes, printable vial labels. PDF.
Bacteriostatic Water Cheat Sheet
How much to add, what one unit holds, the 28-day rule stated correctly, four mistakes to avoid. PDF.
28-Day GLP-1 Injection Tracker
Dose, units drawn, site, weight, side effects and the vial counting down. PDF and spreadsheet.
Other peptide calculators
Arithmetic only. This page converts the dose you enter into units and millilitres. It does not recommend a dose. Retatrutide is not an FDA-approved drug and no human dose-finding trial exists; any dose you enter should come from a prescriber. FormBlends connects patients with licensed providers and pharmacies and does not prescribe or dispense.
