How to Reconstitute a Peptide
To reconstitute a peptide, slowly add bacteriostatic water down the side of the vial, let it dissolve without shaking, then divide the vial strength by the water volume to get a mg/mL concentration. Divide your dose by that concentration to find the volume, and multiply by 100 for units on a U-100 syringe.
For educational and research purposes only. Not medical advice. Always consult a licensed healthcare professional before starting any protocol.
What reconstitution actually does
Most research peptides and compounded GLP-1 medications ship as a lyophilized (freeze-dried) powder. Reconstitution is the process of dissolving that powder in a sterile diluent so it becomes an injectable liquid. It does not change how much peptide you have; it only changes the concentration, which is the amount of peptide per millilitre of liquid.
This matters because your dose is always an amount of peptide in milligrams or micrograms, but what you actually measure on a syringe is a volume. The concentration is the bridge between the two, so getting the reconstitution right is what makes every later dose accurate.
Step by step
First, let both the vial and the bacteriostatic water reach room temperature. Wipe the rubber stoppers with an alcohol swab. Draw your chosen volume of bacteriostatic water into a syringe, then insert the needle into the peptide vial at an angle so the water runs slowly down the inside wall rather than blasting directly onto the powder.
Do not shake the vial. Swirl it gently or let it sit until the powder fully dissolves into a clear solution. Shaking can damage fragile peptide chains and create foam that makes measuring harder. Once dissolved, store the reconstituted vial in the refrigerator.
Turning the mix into a dose
Concentration equals vial strength divided by the water you added. A 5 mg vial reconstituted with 2 mL of bacteriostatic water is 2.5 mg/mL. To find the volume for a dose, divide the dose by the concentration: a 0.25 mg dose at 2.5 mg/mL is 0.1 mL. On a U-100 insulin syringe, multiply the volume in mL by 100 to get units, so 0.1 mL is 10 units.
Choosing how much water to add is a trade-off. Less water gives a stronger solution and a smaller, harder-to-read draw; more water gives a weaker solution and a larger, easier-to-read draw. The peptide amount never changes, only how many units you pull for the same dose.
Frequently asked questions
How much bacteriostatic water should I add?
There is no single correct amount. Pick a volume that makes your dose land on an easy-to-read mark. Adding 2 mL to a 5 mg vial gives 2.5 mg/mL, where a 0.25 mg dose is a clean 10 units. Use the bacteriostatic water calculator to solve for the exact volume that hits the units you want.
Can I shake the vial to dissolve it faster?
No. Shaking can degrade the peptide and introduces foam that makes accurate measuring difficult. Add the water slowly down the vial wall and swirl gently or wait for it to dissolve on its own.
How long does a reconstituted vial last?
Once mixed, keep the vial refrigerated. Bacteriostatic water contains benzyl alcohol that inhibits bacterial growth, which is why it is preferred for multi-dose vials, but shelf life still depends on the specific peptide and storage conditions.
Does adding more water lower my dose?
No. Adding more water only dilutes the solution, so you draw a larger volume for the same milligram dose. The amount of peptide you inject is unchanged.
Related tools
Peptide & GLP-1 Dose Calculator
Free lab-grade calculator for peptide reconstitution and GLP-1 dosing. Calculate your exact dose and see it rendered on a to-scale insulin syringe — semaglutide, tirzepatide, BPC-157 and more.
Bacteriostatic Water Calculator
Free bacteriostatic water calculator: enter your vial strength and dose, then get the exact amount of bac water to add so your dose lands on the units you want, shown on a to-scale insulin syringe.