How to reconstitute peptides
Reconstitution is the step where freeze-dried peptide powder becomes an injectable solution. Done well, it takes about ten minutes and keeps the peptide intact. Done badly, it ruins a vial or turns every dose you draw afterwards into a guess. Here is the whole process, the maths behind it, and the mistakes that cost people vials.
The numbers below assume a 5 mg vial and 2 ml of bacteriostatic water. Run your own vial, water volume and dose through the calculator before you draw anything.
Calculate your unitsWhat you need
Everything below is ordinary pharmacy supply. Have it out and open before the needle comes off anything.
- Lyophilized peptide vialThe freeze-dried powder, usually 2–10 mg per vial.
- Bacteriostatic waterSterile water with 0.9% benzyl alcohol — the preservative that lets a vial be used more than once.
- U-100 insulin syringes0.3, 0.5 or 1 ml. Marks in units, where 100 units = 1 ml.
- Alcohol wipesFor the rubber tops of both vials.
- Sharps containerA rigid, puncture-proof bin for used needles.
- Label and markerTo write the concentration and the day you mixed it.
The maths, in one line each
Three formulas decide every dose you draw from this vial. They are the same three the calculator uses.
Notice what this means practically: the water volume is the number you are choosing, and it sets the concentration for the life of the vial. Change the water and every unit mark you were using is wrong.
The process, step by step
- 1
Wash your hands and clear a space
Wash with soap for 20 seconds and wipe the surface you will work on. Open the alcohol wipes, the syringes and the vials so nothing has to be hunted for mid-way. Everything that touches the inside of a vial should stay sterile — caps off, hands off.
- 2
Work out your concentration first
Decide how much bacteriostatic water you will add before you add it, because that number sets every dose you draw afterwards. Concentration in mcg/ml = vial mg × 1000 ÷ water ml. A 5 mg vial with 2 ml of water gives 2500 mcg/ml, so a 250 mcg dose is 0.1 ml, which is 10 units on a U-100 syringe. The calculator does this for you in one tap.
- 3
Clean both rubber tops
Swab the peptide vial top and the bacteriostatic water top with an alcohol wipe and let both dry on their own — about 30 seconds. Blowing on them or fanning them re-contaminates the surface you just cleaned.
- 4
Draw the air, then the water
Pull the plunger back to your target volume (say 2 ml) so the syringe is full of air, puncture the bacteriostatic water vial, and push the air in first — it equalises the pressure so the water draws back easily. Pull the water down to the line you want, then take the needle out. Do not touch the needle to anything.
- 5
Aim the water at the glass, not the powder
Pierce the peptide vial and push the plunger slowly while holding the needle against the inside wall of the glass, near the top. A steady stream landing straight on the powder can shear the peptide and leave it foamed and clumped. Let the water run down the glass and pool over the powder.
- 6
Let it dissolve — do not shake
Take the needle out, then roll the vial gently between your fingertips or tilt it slowly side to side. Never shake it and never flick it; turbulence and bubbles damage the peptide. Fully clear powder usually disappears in 1–5 minutes. A cold vial straight from the fridge dissolves more slowly, and some peptides take 15–30 minutes; that is normal, so keep waiting rather than adding more water.
- 7
Check the solution before you use it
Hold the vial up to the light. It should be clear and colourless to faintly straw-coloured. Cloudiness, flakes, strings, a yellow-brown tint or powder that never clears are all reasons not to use that vial. Note the colour you started with, so you can spot a change later.
- 8
Label it and refrigerate
Write the peptide name, the concentration (mg/ml or mcg/ml) and the date you mixed it on the vial, then put it in the fridge at 2–8 °C — not the door, where the temperature swings. Most reconstituted peptides are kept for roughly 20–30 days in the fridge; bacteriostatic water only stays effective for about 28 days after the vial is first pierced. Draw each dose from the same vial with a fresh sterile syringe.
- 9
Draw your dose
Wipe the top, invert the vial, and pull back to the unit mark the calculator gave you, keeping the needle tip in the liquid so no air is drawn. Expel any bubble by pointing the needle up, tapping the barrel and pushing the plunger to the correct line. Use the syringe once and put it straight into the sharps container.
Mistakes that ruin a vial
- Shaking or flicking the vialMechanical stress unfolds the peptide. Roll it gently and give it time instead.
- Using plain sterile water for a multi-use vialWithout benzyl alcohol there is no preservative, so the vial is single-use only. Bacteriostatic water is the default for anything drawn more than once.
- Guessing the water volumeThe water amount is the divisor in every dose you draw later. Pick it deliberately and write it on the vial.
- Leaving the vial on the counterHeat and sunlight degrade peptides. Fridge, in the back, away from the door.
- Reusing a syringeThe needle dulls and the hub is no longer sterile after one pass.
- Pushing water straight into the powderAimed at the cake of powder it foams and clumps. Angle it at the glass.
Storage after mixing
Common questions
Do I have to use bacteriostatic water?
For anything you draw from more than once, yes — the 0.9% benzyl alcohol keeps the vial from growing bacteria between uses. Sterile water for injection has no preservative, so a vial mixed with it should be used once and discarded. Plain drinking water, distilled water or saline are not substitutes.
How much water should I add to a vial?
Whatever makes your dose easy to measure — commonly 1, 2 or 3 ml. More water means a weaker solution, so each dose needs more units on the syringe and reads more accurately; less water means a stronger solution and tiny, hard-to-read marks. There is no single right answer, but the number you choose has to be written down and used consistently.
How long does a reconstituted peptide last?
Most are kept about 20–30 days refrigerated at 2–8 °C, and the bacteriostatic water itself is only reliable for roughly 28 days after the vial is first pierced. Some peptides are noticeably less stable than that, so the storage note on the individual peptide page is the one to follow.
Why is my vial cloudy or full of flakes?
Either the powder has not finished dissolving — wait, and roll it gently — or it has degraded or been contaminated. If it stays cloudy, has visible particles, or has changed colour, do not use it.
Can I reconstitute without a syringe?
Not safely. Drawing and injecting need a sterile, graduated syringe to both keep the vial uncontaminated and measure the dose. A syringe is also what lets you add an exact water volume, which is what makes every later dose correct.
Does the water hurt more than the powder?
Reconstituted peptide is usually less stingy than the powder re-solubilised in alcohol, and benzyl alcohol itself has a mild numbing effect. Let the alcohol on the skin dry fully before injecting — that, not the peptide, is what causes most of the sting.
Go deeper
Educational information only, not medical advice. Reconstitution and injection should be taught to you in person by a licensed professional who can confirm your vial, your diluent and your dose. Last reviewed October 2026.