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How to reconstitute semaglutide
Compounded semaglutide arrives as a freeze-dried pellet, so the vial you have is not yet a dose. The thing that makes semaglutide different from every other peptide on this site is its titration ladder: you start at 0.25 mg and finish at 2.4 mg, a nearly tenfold range from one vial. Pick your water volume badly and the early doses become unmeasurable. This page has the chart that avoids that, plus the mixing steps and storage.
Concentration = vial mg ÷ water mL. Units = (dose mg ÷ concentration) × 100 on a U-100 syringe. For a 5 mg vial in 2 mL that is 2.5 mg/mL, which turns the entire approved ladder into clean whole numbers. Or skip the arithmetic with the reconstitution calculator.
What you need
- • A lyophilized semaglutide vial, most commonly 5 mg or 10 mg
- • Bacteriostatic water (sterile water with 0.9% benzyl alcohol). The preservative is what makes repeated withdrawals from one vial acceptable, and semaglutide is a multi-week vial by definition
- • A U-100 insulin syringe for dosing, and a 3 mL syringe for adding the water
- • Alcohol swabs, clean hands, a clean surface
The steps
Prep. Wash your hands. Swab the rubber stopper of both the compound vial and the bacteriostatic water with alcohol and let them air dry.
Draw your water. Pull the volume you decided on above into a syringe. This number is the single decision that sets everything downstream.
Add it slowly. Insert the needle and let the water run down the inside glass wall, not jetting straight onto the powder. Foam means sheared peptide.
Dissolve gently. Swirl the vial or roll it between your palms. Never shake. Wait until it is completely clear. Cloudiness or floating particles means do not use it.
Draw the dose. Work out your units from the chart above, swab the stopper again, and draw on a U-100 syringe, tapping air bubbles back out.
Label and refrigerate. Write the concentration and the date on the vial. In four weeks you will not remember either.
Dose-to-units chart
Semaglutide's approved weight-management ladder is 0.25 → 0.5 → 1.0 → 1.7 → 2.4 mg weekly. Here is what each rung costs you in units at four common reconstitutions:
| Vial + water | Concentration | 0.25 mg | 0.5 mg | 1.0 mg | 1.7 mg | 2.4 mg |
|---|---|---|---|---|---|---|
| 5 mg + 2 mL | 2.5 mg/mL | 10 u | 20 u | 40 u | 68 u | 96 u |
| 5 mg + 1 mL | 5 mg/mL | 5 u | 10 u | 20 u | 34 u | 48 u |
| 10 mg + 2 mL | 5 mg/mL | 5 u | 10 u | 20 u | 34 u | 48 u |
| 10 mg + 1 mL | 10 mg/mL | 2.5 u | 5 u | 10 u | 17 u | 24 u |
Red = the graduation is too fine to draw accurately. A U-100 syringe is marked in whole units; half a unit is a guess.
Which water volume to actually use
5 mg vial with 2 mL of bacteriostatic water is the setup worth defaulting to, and it is not arbitrary. At 2.5 mg/mL every rung of the ladder lands on a round, easily-read number, the starting 0.25 mg dose is a comfortable 10 units rather than a squint, and the top 2.4 mg dose is 96 units, which still fits inside a single U-100 syringe with room to spare.
Go more concentrated and the low end falls apart. A 10 mg vial in 1 mL gives 10 mg/mL, where your first dose is 2.5 units. There is no honest way to draw 2.5 units on a syringe marked in single units, and a half-unit error at that concentration is a 20% dosing error. If you are handed a 10 mg vial, put 4 mL in it and you are back to 2.5 mg/mL.
The one reason to go the other way is vial life. Semaglutide is dosed weekly, so a 5 mg vial at the 0.25 mg starting dose contains twenty weeks of medication, far beyond any sensible beyond-use date. Mix the smaller vial, not the bigger one, and accept that you will discard some.
How this compares to the pen
Prefilled Ozempic and Wegovy pens are already in solution and are dosed by clicking to a marked dose, not by drawing units, which is why pen instructions are no help here. The pens also sit at concentrations chosen by the manufacturer rather than by you. If you are moving from a pen to a compounded vial, the only number that carries over is the dose in mg. Everything about how you measure it changes, so recompute rather than assuming your old click count means anything.
Storage & beyond-use dating
Dry, unreconstituted semaglutide is comparatively robust. Once it is in solution it is not. The working default is about 28 days refrigerated at 2-8 °C, which for weekly dosing is roughly four doses out of one mix. Keep it cold and out of light, never freeze it, minimise the time it spends on the counter while you draw, and discard on the date you wrote on the label rather than the date you think you remember. If a vial looks cloudy, has particles, or has been through a warm car, it goes in the bin regardless of what the calendar says. See the peptide storage guide for the full stability picture.
Common mistakes
- • Reconstituting a 10 mg vial in 1 mL and then starting at 0.25 mg. That is a 2.5-unit draw. Use more water.
- • Copying a units number off a forum without checking their vial size and water volume. Units are meaningless without a concentration attached.
- • Confusing mg with units. 2.4 mg is not 2.4 units. At 2.5 mg/mL it is 96 units, forty times the number.
- • Mixing the whole 10 mg vial while on a starting dose. You will not use it before the beyond-use date.
- • Shaking to speed dissolution. Swirl. Foam damages the peptide.
This page explains the mechanics of reconstitution. It is not medical advice, a prescription, or an endorsement of compounded semaglutide over an approved product. Compounded and research-use vials are not subject to the quality control that approved pens are, and stated strength, purity and sterility can all be wrong, which no amount of careful mixing corrects. The FDA has warned specifically about dosing errors with compounded semaglutide drawn from vials. Any decision about using it belongs with a licensed clinician.
Skip the arithmetic
OptiPin's free reconstitution calculator takes your vial size, water volume and target dose and returns the exact units, flagging the draws that will not fit a syringe. The app then logs every injection, tracks what is left in the vial and warns you before it runs out or expires. iOS, on-device, no account.
Open the calculatorFrequently asked questions
How much bacteriostatic water for 5 mg of semaglutide?
Two millilitres is the most useful default. That gives 2.5 mg/mL, which turns the entire 0.25 to 2.4 mg titration ladder into clean whole-unit draws: 10, 20, 40, 68 and 96 units respectively. One millilitre also works and halves those numbers, but it makes the 0.25 mg starting dose a 5-unit draw where a one-unit error is a 20% dose error.
How many units is 0.25 mg of semaglutide?
It depends entirely on your concentration. With a 5 mg vial in 2 mL of bacteriostatic water (2.5 mg/mL), 0.25 mg is 10 units on a U-100 syringe. With a 10 mg vial in 2 mL (5 mg/mL) the same dose is 5 units. Recompute from your own vial rather than reusing anyone else's figure.
How do I reconstitute a 10 mg semaglutide vial?
Use 4 mL of bacteriostatic water to land at 2.5 mg/mL, matching the 5 mg + 2 mL setup and keeping the whole ladder readable. Two millilitres gives 5 mg/mL, which is workable but makes the early doses small. Avoid 1 mL, which produces 10 mg/mL and an unmeasurable 2.5-unit starting dose.
How long does reconstituted semaglutide last?
About 28 days refrigerated is the common working figure, though it depends on the diluent, the storage conditions and the product itself. At weekly dosing that is roughly four doses per mix. Keep it at 2-8 °C, out of light, never frozen, and discard on your labelled date.
Can I use sterile water instead of bacteriostatic water?
Not for a multi-dose vial. Plain sterile water has no preservative and is intended for a single withdrawal, whereas semaglutide vials get punctured weekly for a month. Bacteriostatic water contains 0.9% benzyl alcohol precisely so that repeated entries do not turn the vial into a culture medium.
Sources & further reading
- Bacteriostatic Water for Injection, USP - DailyMed label (0.9% benzyl alcohol; the standard multi-dose diluent).
- FDA - concerns with unapproved GLP-1 drugs used for weight loss (documented dosing errors from compounded vials).
- USP General Chapter <797> - Sterile Compounding (aseptic technique and beyond-use dating).
U-100 syringe: 100 units = 1 mL. Vial strengths and fill volumes vary between suppliers, so always verify the stated strength on your own vial before calculating. This page is educational and is not medical advice.
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