How to Reconstitute Semaglutide (Step by Step)

By DoseGauge Editorial · Updated 2026-06-12 · 5 min read

Reconstituting semaglutide means adding a liquid (bacteriostatic water) to a vial of dry powder so the medication can be drawn into a syringe. The volume of water you add decides the concentration, the concentration decides how many units equal your dose, and a calculator does that conversion from your two inputs. The approved semaglutide pens (Ozempic and Wegovy) ship as ready-to-use solutions. Reconstitution applies to lyophilized (freeze-dried) semaglutide powder supplied in a vial.

What you need

Three things. A vial of lyophilized semaglutide of a known strength in milligrams. A vial of bacteriostatic water, which is sterile water for injection containing benzyl alcohol as a preservative so the vial can be used for repeated withdrawals. And a U-100 insulin syringe, which is marked in units where 100 units equal 1 mL. For more on the diluent and why a preservative matters, see what is bacteriostatic water.

Work on a clean surface, wipe both vial stoppers with an alcohol swab, and use a new sterile syringe.

You also need one decision before you touch the vial: how much water to add. That single choice fixes the concentration of the whole vial, and the concentration is what turns your milligram dose into a number of syringe units. Semaglutide doses are small (often a fraction of a milligram), so concentration choice has a large effect on how readable the resulting unit count is. More water gives a lower concentration and larger unit counts. Less water gives a higher concentration and smaller draws.

Step by step

1. Decide how much bacteriostatic water to add. This sets your concentration, so pick the volume before you start. The calculator can show you the units that result from each volume.
2. Draw your chosen volume of bacteriostatic water into the syringe.
3. Insert the needle into the powder vial and inject the water slowly against the inside glass wall, letting it run down rather than splashing onto the powder.
4. Remove the needle and swirl the vial gently. Do not shake it. Peptides are fragile, and shaking can foam or stress the molecule.
5. Let it sit until the solution is fully clear with no visible particles. This can take a few minutes.
6. Store the vial in the refrigerator. Label it with the date and concentration so you know what you have.

The reconstitution math

Three formulas turn the vial and water into a number of units to draw:

concentration (mg/mL) = vial strength (mg) / water added (mL)
draw volume (mL)       = dose (mg) / concentration (mg/mL)
units (U-100 syringe)  = draw volume (mL) x 100

Worked semaglutide example. Take a 5 mg vial and add 2 mL of bacteriostatic water. The concentration is 5 / 2 = 2.5 mg/mL. For a 0.25 mg dose, the draw volume is 0.25 / 2.5 = 0.10 mL, which is 10 units on a U-100 syringe. That vial holds 5 / 0.25 = 20 doses of 0.25 mg. Add 1 mL of water instead and the concentration doubles to 5 mg/mL, so the same 0.25 mg dose becomes 0.05 mL, or 5 units.

Rather than redo this arithmetic by hand each time you change a vial or water amount, enter your numbers and read the units directly. The full method and rounding behavior are documented on the methodology page.

A short word on reading the syringe. A U-100 insulin syringe is graduated so that 100 units equal 1 mL, which means 1 unit equals 0.01 mL. When the calculator returns 10 units, you draw to the 10 mark. Small semaglutide doses can land on low unit counts, so a more dilute mix often makes the dose easier to measure accurately.

Storage and handling

Keep the reconstituted vial refrigerated and protected from light, and use it within the period your pharmacy or supplier specifies for the product you have. The benzyl alcohol in bacteriostatic water inhibits microbial growth, which is what makes a multiple-dose vial reasonable in the first place, but it is not a substitute for clean technique. Discard the vial if the solution turns cloudy, changes color, or shows particles.

Frequently asked questions

How much bacteriostatic water do you add to semaglutide?

There is no single correct volume. It depends on the concentration you want and the number of units you find comfortable to measure. Because semaglutide doses are small, a more dilute mix often gives larger, easier-to-read unit counts. Enter your vial strength and a candidate water volume in the calculator to see the resulting units before you commit.

Can you shake the vial?

The standard guidance for reconstituting lyophilized peptides is to swirl gently and avoid shaking. Inject the water down the glass wall and rotate the vial slowly until the powder dissolves.

Does the powder need to dissolve completely before use?

Yes. Wait until the solution is fully clear with no visible particles before drawing a dose. If particles remain after several minutes of gentle swirling, do not use the vial.

What happens if you add the wrong amount of water?

The amount of drug does not change, but the concentration does, so every unit count you calculated becomes wrong. More water than planned makes the solution more dilute and each dose takes more units. Less water makes it more concentrated and each dose takes fewer units. Recompute from the actual milligrams in the vial and the actual milliliters you added.

Informational and educational only. Not medical advice. DoseGauge computes from the values you enter and does not recommend a dose. Talk to a licensed clinician before using any peptide or GLP-1 medication.