Supplies You Need
Gather everything before starting. Working from a clean, complete setup is what prevents contamination and measurement mistakes — improvising mid-process is where errors creep in.
- The peptide vial — lyophilized powder, sealed with a rubber stopper and aluminum crimp cap. Leave the crimp cap in place; the stopper is punctured through it.
- Bacteriostatic water (BAC water) — sterile water with 0.9% benzyl alcohol as a preservative, typically supplied in 10 mL or 30 mL multi-dose vials.
- Insulin syringes — a 1 mL (U-100) syringe for adding diluent, since most reconstitutions call for 1–3 mL, and smaller syringes for drawing individual doses.
- Alcohol swabs — one per stopper, per puncture. Non-negotiable.
- A sharps container — for immediate, safe disposal of used syringes.
Choosing a Diluent
Bacteriostatic water is the default diluent for peptide reconstitution, and for good reason: its 0.9% benzyl alcohol content suppresses bacterial growth across repeated punctures, which is what allows a reconstituted vial to be used for multiple doses over roughly 25–30 days rather than a single sitting.
Sterile water, by contrast, contains no preservative. If used, the resulting solution should be treated as short-lived and discarded within 24–48 hours, since bacterial growth becomes a real risk the moment the vial is punctured. For any protocol spanning more than one or two doses, bacteriostatic water is the appropriate choice.
Never substitute tap water, off-the-shelf distilled water, or any liquid that is not labeled sterile and intended for injection. These carry contaminants that pharmaceutical-grade diluents are specifically manufactured to exclude.
Why the Water Volume Sets the Concentration
The amount of diluent added is not a matter of preference — it directly sets the concentration of the resulting solution, and concentration is what every later dose calculation depends on.
Concentration (mg/mL) = total peptide in the vial ÷ volume of diluent added.
Add less water and the solution becomes more concentrated — each dose occupies a smaller syringe volume, which can be harder to measure precisely on a larger-barrel syringe. Add more water and the solution becomes more dilute — each dose takes up more volume, which is easier to read but may not fit a very small syringe. There is no universal correct amount; the right choice is whichever volume produces a dose that lands cleanly on the available syringe's markings. This is exactly what our recipes and calculator are built to solve.
Step-by-Step Reconstitution
- Prepare the workspace. Clean, flat surface. Let a refrigerated vial sit for a few minutes to approach room temperature — reconstituting straight from cold can slow dissolution.
- Sterilize both stoppers. Wipe the BAC water vial's stopper with an alcohol swab, then use a fresh swab for the peptide vial's stopper. Let both air-dry for a few seconds.
- Draw the diluent. Insert the needle into the inverted BAC water vial and pull back slowly to the volume specified in the recipe.
- Add it down the vial wall. Insert the needle through the peptide vial's stopper and aim the stream at the interior glass wall, not directly onto the powder. Depress the plunger slowly, letting the liquid trickle down onto the cake.
- Swirl, don't shake. Remove the syringe and rotate the vial gently between the fingers. Shaking introduces shear forces and foaming that can damage the peptide; a gentle swirl dissolves it just as effectively without that risk.
- Inspect. Hold the vial to light. The solution should turn clear and colorless, typically within 1–3 minutes, occasionally up to 10 for larger or more complex peptides. Persistent cloudiness after extended swirling is a signal to stop and reassess, not to proceed.
- Label and refrigerate. Note the reconstitution date and diluent volume on the vial, then refrigerate immediately.
A Worked Example
Suppose a vial contains 5 mg of peptide and the recipe calls for 2 mL of bacteriostatic water.
Concentration: 5 mg ÷ 2 mL = 2.5 mg/mL.
If the target dose is 250 mcg (0.25 mg), the dose volume is:
Dose volume (mL) = target dose (mg) ÷ concentration (mg/mL) = 0.25 ÷ 2.5 = 0.10 mL.
Converted to a U-100 insulin syringe, where 1 unit = 0.01 mL, that is 10 units. The same vial, at that dose, yields 5 mg ÷ 0.25 mg = 20 total doses. This three-step chain — concentration, then dose volume, then syringe units — is identical for every peptide and every vial size. Our syringe measurement guide covers the conversion in more depth, and the calculator on each protocol page runs this exact math against specific, entered numbers.
After Reconstitution
Once reconstituted, refrigerate the vial at 2–8°C immediately and store it upright — laying it on its side lets solution pool against the stopper, which can degrade the seal over time. Most peptides reconstituted with bacteriostatic water remain usable for roughly 25–30 days under refrigeration; never freeze a reconstituted solution, since ice crystals physically damage peptide structure. For the complete storage rules, before and after reconstitution, see our storage guide.