How to Reconstitute Peptides: The Complete Guide

Written and reviewed by Evan Marlow, developer of DosePlot · Updated 2026-08-27

Reconstituting a peptide means dissolving a freeze-dried powder in liquid so you can draw and inject it. You add a measured amount of bacteriostatic water to the vial, and the amount you choose sets the concentration — which decides how many units you draw for each dose. Everything else in this guide is detail on those two choices: which water, and how much.

What does reconstituting a peptide actually involve?

Four steps, in order. None of them is difficult; the judgment is all in step 2.

1. 1. Pick your water

   For a vial you'll draw from more than once, bacteriostatic water — it contains a preservative that lets you make repeated withdrawals over days or weeks.^[1] Plain sterile water has no preservative and is single-use.

2. 2. Choose how much water to add

   This is the only real decision. More water spreads the same peptide across a larger volume, so each dose is a larger, easier-to-read draw; too little water can leave the powder undissolved and make each dose an unreadably tiny number of units.

3. 3. Add the water and let it dissolve

   Run the water gently down the inside of the vial onto the powder, then let it dissolve on its own or swirl slowly. Don't shake hard — foaming and shear can damage some peptides.

4. 4. Draw your dose and store the vial

   Read the draw in units on a U-100 insulin syringe, then refrigerate the mixed vial. A punctured multi-dose vial is dated and used within about a month, and never past the printed expiry.^[2]

Why the water volume is the whole game

The peptide amount is fixed — it's whatever the vial holds. All the water changes is how concentrated the solution is, and therefore how big each draw is. Same 5 mg vial, two different water volumes:

Illustrative arithmetic only — not a dose. Concentration = peptide mass ÷ water added; units = draw volume × 100 on a U-100 syringe. Your compound and dose are your own; the calculator does your exact numbers.

The full guide

Reading the dose on the syringe

Reconstituted peptides are drawn on a U-100 insulin syringe, where 100 units equal 1 mL. Once you know your concentration, the draw in units is just the dose divided by the concentration, times 100. The insulin-syringe units guide covers reading the barrel without mistakes, and the peptide needle guide covers which syringe to use.