What you need
- The peptide vial (lyophilized powder)
- Bacteriostatic (BAC) water
- Alcohol swabs
- A U-100 insulin syringe
- A pen or label for the vial
Step-by-step reconstitution
- Wash your hands. Wash and dry your hands before you open anything.
- Swab both stoppers. Wipe the rubber stopper on the peptide vial and the rubber stopper on the BAC water vial with a fresh alcohol swab, and let them air dry for a few seconds.
- Draw the BAC water. Decide the volume of BAC water you're adding, then draw exactly that amount into the syringe. This volume is what sets the concentration, so pull it carefully to the marking.
- Add the water down the inside wall of the vial. Insert the needle into the peptide vial at an angle and let the water run slowly down the inside glass wall, so it pools at the bottom, rather than spraying it directly onto the powder.
- Swirl gently. Don't shake. Tilt and roll the vial gently in your hand so the liquid moves over the powder. Shaking introduces air and foam, which is unnecessary and makes the vial harder to read.
- Let it dissolve completely. Give it a little time until the solution is clear, with no powder or clumps left on the glass or the stopper.
- Label the vial. Write the date you reconstituted it and the resulting concentration (for example, "5 mg in 2 mL, 2,500 mcg/mL") on the vial or its box. This one habit prevents most of the mix-ups described below.
Calculating the draw
Once the vial is mixed, the amount of BAC water you added and the amount printed on the vial together set the concentration. From there, working out how much to draw for a given amount is arithmetic, not guesswork. Doing it by hand every time is where mistakes creep in, which is the whole reason a peptide reconstitution calculator is useful: it does the same three steps below without letting a misplaced decimal point through.
concentration (mcg/mL) = vial amount (mcg) ÷ BAC water added (mL) volume to draw (mL) = amount you want (mcg) ÷ concentration (mcg/mL) units on a U-100 syringe = volume to draw (mL) × 100Worked example. A 5 mg vial is 5,000 mcg. Add 2 mL of BAC water and the concentration is 5,000 ÷ 2 = 2,500 mcg/mL. To draw an example amount of 250 mcg, divide: 250 ÷ 2,500 = 0.10 mL, which is 10 units on a U-100 syringe. The whole vial holds 5,000 ÷ 250 = 20 draws of that size. Plug your own vial size, water and target amount into the calculator to skip the arithmetic.
Storage: how long a reconstituted vial lasts
Once a peptide is in solution, keep the vial refrigerated, roughly 36–46°F (2–8°C), and wipe the stopper with a fresh alcohol swab before every single draw.
How long it stays usable depends on the specific compound, so there isn't one number that fits every peptide. As a reference point, PeptidesAI's own in-app guidance describes most reconstituted peptides as stable for roughly 2 to 6 weeks under refrigeration, and describes some peptides as more fragile, recommending they be used within about 30 days. The app's built-in vial-expiry reminder defaults to 28 days after you log a reconstitution, which is a general-purpose default rather than a figure specific to any one compound. For the number that applies to your vial, check the supplier's documentation for that peptide rather than relying on a single rule of thumb.
Common mistakes
- Mixing up mg and mcg. 1 milligram (mg) is 1,000 micrograms (mcg). A vial labeled in mg and a target amount written in mcg are easy to confuse, and because the conversion factor is 1,000, the resulting error is large, not a small rounding slip. Convert everything to mcg before you do any other math.
- Using the wrong syringe type. The math above, and the calculator, assume a U-100 insulin syringe, where 100 units equal 1 mL. A U-40 syringe holds the same kind of markings but on a different scale, so reading a U-100 volume off a U-40 barrel (or the reverse) gives you the wrong draw.
- Not recording the concentration. If you don't label the vial with the date and the resulting mcg/mL, you're left guessing later, especially once you've combined more than one vial in a stack. Writing it down once at reconstitution is faster than recomputing it from memory every time.
Frequently asked questions
Can I spray the BAC water directly onto the powder?
It's better not to. Letting the water run down the inside wall of the vial so it pools at the bottom is gentler on the powder than a direct stream.
Why can't I shake the vial?
Shaking introduces air into the liquid and creates foam. A slow, gentle swirl mixes the powder without doing that.
How long does a reconstituted vial last?
It depends on the specific peptide, so there is no single number that applies to all of them. As a general reference, PeptidesAI's own guidance describes most reconstituted peptides as stable for roughly 2 to 6 weeks under refrigeration, with some described as more fragile and best used within about 30 days, and the app defaults its vial-expiry reminder to 28 days after reconstitution. Check the specific compound's supplier documentation for the number that applies to your vial.
Do I need to refrigerate a reconstituted vial?
Yes. Once a peptide is in solution it should be kept refrigerated, roughly 36–46°F (2–8°C), and the stopper should be wiped with alcohol before every draw.
What is the biggest reconstitution math mistake?
Mixing up milligrams and micrograms. 1 mg equals 1,000 mcg, so an error here is a 1,000-fold error, not a rounding difference.
Do I need a special syringe?
Use a U-100 insulin syringe, where 100 units equal 1 mL. A U-40 syringe uses a different scale and will give you the wrong volume if you read U-100 numbers off it.
Do this math once, not every time
PeptidesAI saves each vial's concentration, tells you the units for every draw, tracks how much is left and reminds you before it expires. Free to download on iPhone.
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