BioChonch, Founder, BodyHackGuide · Jul 7, 2026 · Fact-checked

How to Reconstitute Peptides

Q: How do I calculate the concentration after reconstituting?

Divide the vial mass by the volume of water you added: mg divided by mL = mg/mL. A 10 mg vial in 2 mL is 5 mg/mL. To convert to syringe units on a U-100 scale, use the reconstitution calculator.

A step-by-step lab-prep walkthrough — for research use only. This covers mixing and concentration math, not dosing.

Research use only. This guide describes reconstitution — dissolving a lyophilized research compound and calculating its concentration. It is not administration, dosing, or medical guidance.

Reconstitution is the least glamorous and most botched step in working with research peptides. The compound arrives as a freeze-dried plug at the bottom of a vial, and before you can measure anything you have to put it back into solution correctly. Do it wrong and you either damage the peptide or, more commonly, have no idea what concentration you are actually holding. Here is the whole process, framed as lab prep.

What you'll need

Your lyophilized peptide vial — with its Certificate of Analysis. Reconstitute against the tested mass on the COA, not the number printed on the label. (New to COAs? Here is how to read one.)
Bacteriostatic water — sterile water with about 0.9% benzyl alcohol, which allows repeated entry into a multi-use vial without spoilage. BHG Labs stocks lab-grade BAC water. Independent vendor; BodyHackGuide may earn a commission. BHG Labs is not BodyHackGuide.
A sterile syringe to measure and transfer the water (a 1–3 mL syringe for the water; a U-100 insulin syringe for reading small volumes).
Alcohol wipes for the vial stoppers.
The reconstitution calculator so you are not doing mg/mL in your head.

Step 1 — Decide your water volume first

Before you touch anything, pick how much bacteriostatic water you are adding, because that single choice sets your concentration. Less water gives a stronger, more compact solution with tiny draws; more water gives a weaker solution that is easier to measure but empties the vial faster. Common research volumes are 1–3 mL per vial. Plug your vial mass and intended water volume into the calculator up front so you know the concentration you are about to create.

Step 2 — Prep both vials

Wipe the rubber stopper on the peptide vial and the bacteriostatic water vial with an alcohol wipe and let them dry. Draw your chosen volume of bacteriostatic water into the syringe, measuring at eye level so the meniscus sits exactly on your mark.

Step 3 — Add the water slowly, down the glass

Insert the needle into the peptide vial and angle it so the water runs down the inside wall of the vial, not directly onto the powder. Let it trickle in slowly. Firing a hard stream straight into the lyophilized plug is one of the few ways to physically stress the peptide before it is dissolved.

Step 4 — Swirl, never shake

Remove the needle and gently swirl the vial until the solution turns clear. Do not shake it. Shaking whips air into the solution and the mechanical shear can denature fragile peptides. Most compounds dissolve in under a minute of slow swirling. A properly reconstituted vial is clear, not cloudy.

Step 5 — Confirm your concentration

Now the concentration is locked in by simple arithmetic: mass ÷ volume = mg/mL. A 10 mg vial in 2 mL of bacteriostatic water is 5 mg/mL. That is the number that matters, and it does not change unless you add more liquid. The calculator also converts it to units on a U-100 insulin syringe (100 units = 1 mL), so you can read draws off the scale instead of eyeballing millilitres.

Worked example

Say the COA confirms a 10 mg vial and you add 2 mL of bacteriostatic water:

Concentration = 10 mg ÷ 2 mL = 5 mg/mL
On a U-100 syringe, 0.05 mL = 5 units, and that 5-unit draw contains 0.25 mg

Change nothing but the water — use 1 mL instead of 2 mL — and the same vial becomes 10 mg/mL. The identical 5-unit draw now holds 0.5 mg. Same powder, same syringe mark, double the mass, entirely because of the water volume. That is why “how much water” is the only real decision in reconstitution.

Storage after reconstitution

Once it is in solution, a peptide is far less stable than it was as a powder. For research handling, reconstituted vials are generally kept refrigerated (not frozen — freeze-thaw cycling is hard on peptides) and protected from light. Label the vial with the concentration and the date you mixed it, because a month later you will not remember whether it was 5 or 10 mg/mL.

The three inputs that cause every error

Almost every “the numbers do not make sense” problem traces to one of three inputs: the vial mass (use the COA, not the label), the exact water volume you added, and the syringe scale you are reading (U-100 vs U-40 vs U-50 are marked differently). Nail those three and reconstitution is genuinely just division.

FAQ

How much bacteriostatic water should I use to reconstitute a peptide?

There is no single correct amount — it is a trade-off you set. Less water means a higher concentration and smaller draws; more water means a lower concentration that is easier to measure but empties the vial faster. Research volumes are commonly 1–3 mL per vial. Use the calculator to see the exact concentration and syringe units any volume produces before you commit.

Can I use regular sterile water or saline instead of bacteriostatic water?

For a multi-use vial you will enter more than once, bacteriostatic water is the standard because its benzyl alcohol preservative resists microbial growth across repeated draws. Plain sterile water and saline lack that preservative and are not intended for repeated entry.

Why shouldn't I shake the vial?

Shaking forces air into the solution and creates mechanical shear that can denature fragile peptide molecules. Gentle swirling dissolves the powder without that stress. Reconstitution should look calm and boring — clear solution, no foam.

How do I calculate the concentration after reconstituting?

Divide the vial mass by the volume of water you added: mg ÷ mL = mg/mL. A 10 mg vial in 2 mL is 5 mg/mL. To convert that to syringe units on a U-100 scale, or to check any draw, use the reconstitution calculator.

How long does reconstituted peptide last?

It depends on the specific compound, but a reconstituted solution is always less stable than the dry powder. For research handling it is generally kept refrigerated, protected from light, and labeled with the mix date. Favor smaller water volumes you will use up sooner over large volumes that sit for weeks.

Research disclaimer: this guide is for educational and research purposes only and is not medical advice. Compounds referenced are research-use-only and not for human consumption.