How to Reconstitute Peptides: Step-by-Step

Reconstituting a peptide means mixing the freeze-dried (lyophilized) powder inside a sealed vial with bacteriostatic water so it becomes an injectable solution. The procedure takes about two minutes once your supplies are out. The math — how much water to add — determines how many syringe units equal one dose, so we cover it in detail below and link to the free calculator.

Supplies you need

• The peptide vial (lyophilized powder, sealed glass).
• Bacteriostatic water (BAC water) — see the BAC water guide for what it is and why.
• One U-100 insulin syringe (0.5 mL or 1 mL barrel, 29G–31G needle) for measuring and adding BAC water.
• Alcohol swabs.
• A sharps container.

Optional: a second syringe per draw if you prefer never to reuse a needle, though many users reuse the same insulin syringe across one to three draws if technique is clean and the needle is still sharp.

The reconstitution procedure

1. Decide how much BAC water to add. The volume of BAC water determines the final concentration. A common default is to choose a BAC volume that makes one dose equal a round number of insulin syringe units — for example, 10 units (0.1 mL) per dose. See "Choosing the BAC water volume" below.
2. Swab both stoppers. Wipe the BAC water vial stopper and the peptide vial stopper with an alcohol swab. Let them air-dry for a few seconds.
3. Draw the BAC water. Pull air into the syringe equal to the BAC volume you plan to inject (this helps equalize pressure). Insert the needle into the BAC water vial, push the air in, invert, and draw the planned volume. Tap any bubbles to the top and push them back out.
4. Add the BAC water to the peptide vial slowly. Insert the needle through the peptide-vial stopper, angle the tip to the inner glass wall, and depress the plunger so the BAC water trickles down the side of the vial. Do not blast it directly onto the powder — fast streams can shear or denature peptide.
5. Swirl gently — do not shake. Hold the vial between thumb and forefinger and roll it in slow circles for ten to fifteen seconds. The powder should dissolve into a clear (sometimes faintly tinted) solution. If a fine flake or residue persists for thirty seconds, let it sit at room temperature for five minutes and swirl again. Shaking creates foam, which makes the solution hard to draw cleanly and can degrade peptide.
6. Inspect the solution. A correctly reconstituted vial is clear or very slightly opalescent. Visible particulates, color, or cloudiness mean something is wrong — discard the vial.
7. Refrigerate. Store at 2–8 °C between doses.

That's it.

Choosing the BAC water volume

The volume determines the concentration:

• Concentration (mg/mL) = vial powder (mg) ÷ BAC water added (mL).

And the concentration determines the dose volume:

• Dose volume (mL) = dose (mg) ÷ concentration (mg/mL).

And the dose volume in mL converts to insulin-syringe units:

• Syringe units = dose volume (mL) × 100 for a U-100 syringe.

The right BAC volume for your dose is the one that makes the per-dose syringe reading land on a number you can read precisely. If you have to dial in 2.3 units repeatedly, your dose accuracy is going to suffer. Most users aim for a per-dose reading between 5 and 25 units.

To skip the arithmetic and validate your choice, run the numbers through the reconstitution calculator. It will tell you if the BAC volume you're considering gives an awkward per-dose reading.

Worked example: BPC-157

You have a 5 mg vial of BPC-157 and you want to dose 250 mcg (0.25 mg) per shot.

• Add 2 mL of BAC water.
• Concentration: 5 mg ÷ 2 mL = 2.5 mg/mL.
• Dose volume: 0.25 mg ÷ 2.5 mg/mL = 0.1 mL.
• Syringe units: 0.1 mL × 100 = 10 units on a U-100 insulin syringe.

That's a clean, easy-to-read draw. Twenty doses come out of one vial.

Worked example: GLP-1 (Semaglutide-class)

You have a 10 mg vial of Semaglutide and you want to dose 0.25 mg per shot to start.

• Add 2 mL of BAC water.
• Concentration: 10 mg ÷ 2 mL = 5 mg/mL.
• Dose volume: 0.25 mg ÷ 5 mg/mL = 0.05 mL.
• Syringe units: 5 units on a U-100 insulin syringe.

For a 0.5 mg titration step, the same vial reads 10 units per dose.

Storage and shelf life

Refrigerate the reconstituted vial at 2–8 °C. Most peptides remain potent for four to eight weeks reconstituted; specific stability profiles vary, so check the relevant page in the peptide library for the compound you're using.

USP labels BAC water itself as safe for up to 28 days post-puncture due to preservative depletion. In practice the limiting factor for most peptide vials is the peptide's own stability, not the BAC water. Either way, discard a vial showing visible particulates, color change, or cloudiness regardless of the date on it.

Common mistakes

A handful of mistakes recur:

• Picking BAC volume by habit instead of math. "Always 1 mL" produces wildly different per-dose readings depending on the vial size. Run the calculation for every new peptide.
• Blasting the BAC water onto the powder. Trickle it down the inner glass wall instead.
• Shaking the vial. Swirl or invert; never shake.
• Using sterile water or saline for a multi-dose vial. Neither has a preservative — see the BAC water guide.
• Reading the syringe wrong. A U-100 insulin syringe shows 100 units = 1 mL. A 0.5 mL barrel still uses U-100 graduations, just with fewer of them. Double-check your barrel before your first draw.

What's next

Once the peptide is reconstituted, the next operational step is administration. See how to inject peptides for the subcutaneous technique and where to inject peptides for site selection and rotation. For dose-level safety considerations and side-effect data, see are peptides safe?.