Peptide Dosage: How to Reconstitute & Dose Correctly
Reconstituting a peptide comes down to one relationship between three numbers: how much peptide is in the vial, how much water you add, and the dose you want. Get those straight and the “units to draw” falls out automatically. Here’s exactly how it works, with a worked example.
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The one formula you need
After you mix a freeze-dried (lyophilized) vial with bacteriostatic water, its concentration is simply:
concentration = vial amount (mg) ÷ water added (mL)
To turn a dose into insulin-syringe units, convert everything to the same unit (micrograms), divide the dose by the concentration to get the volume, and multiply by 100 — because on a U-100 syringe, 100 units = 1 mL. That’s the whole thing. The calculator runs it instantly, but it helps to see it once.
A worked example: BPC-157
Say you have a 5 mg vial of BPC-157 and you want a 250 mcg dose. Watch what happens to the units as you change only the water — the dose never changes:
| Water added | Concentration | Draw for 250 mcg |
|---|---|---|
| 1 mL | 5 mg/mL | 5 units |
| 2 mL | 2.5 mg/mL | 10 units |
| 3 mL | 1.67 mg/mL | 15 units |
All three deliver the exact same 250 mcg. More water just spreads that dose across more units, which makes it easier to measure accurately on the syringe. A 5 mg vial at 250 mcg also gives you 20 doses (5,000 mcg ÷ 250), whatever water you chose.
mcg vs mg — the mistake that matters most
Vials are labelled in milligrams; doses are frequently written in micrograms. Since 1 mg = 1,000 mcg, confusing the two is a thousand-fold error — the difference between a 250 mcg dose and a 250 mg one. Before you calculate anything, make sure the dose unit you enter matches what you actually intend. The calculator lets you pick mcg or mg per field for exactly this reason.
How much water should I add?
It’s your choice, and it doesn’t change your dose — only how many units you draw. 1–3 mL is typical. Two practical rules of thumb:
- Small doses → more water. If a dose comes out to only 1–2 units, add more water so it lands on a larger, easier-to-read number.
- Watch the syringe limit. If a dose needs more units than your syringe holds (e.g. over 100 on a 1 mL barrel), use less water or a larger syringe. The calculator flags this automatically.
What to reconstitute with
For almost all peptides, the right solvent is bacteriostatic water — sterile water with 0.9% benzyl alcohol. That preservative is what lets you enter the vial repeatedly over several weeks without it spoiling, which is why it’s the default for multi-dose peptide vials.
- Bacteriostatic water — the standard choice; good for roughly 28 days refrigerated once mixed.
- Sterile water — no preservative, so it’s meant for single use; a mixed vial should be used quickly rather than stored for weeks.
- Dilute acetic acid — occasionally used first for peptides that don’t fully dissolve in water, then diluted with bacteriostatic water to the working volume. Follow the specific peptide’s handling notes.
Add the water slowly against the vial wall and let the powder dissolve on its own — don’t shake it hard. Whatever you use, the volume you add is what sets your concentration, so measure it.
Blends and stacks
Some vials contain more than one peptide premixed in the same water — a “blend,” like BPC-157/TB-500. Because they share the water, every unit you draw contains a fixed ratio of each compound, so you can’t dose them separately. Our blend calculator shows exactly how much of each peptide is in a given draw.
Common mistakes to avoid
- Sloppy reconstitution. Adding a different amount of water than you calculated for changes the concentration and throws off every dose. Measure the water.
- Unit mix-ups. mcg vs mg, and insulin “units” vs millilitres — keep them straight.
- Ignoring the syringe cap. A dose that needs 150 units won’t fit a 100-unit syringe; re-mix with less water.
- Contamination. Swab the stopper with alcohol and don’t touch needle tips — see aseptic technique.
Storing a reconstituted vial
Lyophilized (freeze-dried) powder is stable and can sit in the freezer until you need it. Once you’ve added water, though, the clock starts. A reconstituted vial is generally kept refrigerated (about 2–8 °C) and used within roughly 28 days, though the exact window varies by peptide.
- Refrigerate after mixing — don’t leave a reconstituted vial at room temperature for long.
- Don’t freeze the reconstituted liquid — repeated freeze-thaw cycles can degrade many peptides. Freeze the dry powder, not the solution.
- Keep it out of direct light, and swab the stopper with alcohol before each draw.
- Label the vial with the contents, concentration, and the date you reconstituted it, so you can track the 28-day window.
Peptide dosage FAQ
What is the difference between micrograms (mcg) and milligrams (mg)?
1 milligram (mg) equals 1,000 micrograms (mcg). Vials are usually labelled in mg while doses are often written in mcg, so converting both to the same unit is the first thing any calculation does — and mixing them up is a 1,000× error.
Does adding more or less bacteriostatic water change my dose?
No. Water only changes the concentration — and therefore how many units you draw — not the amount of peptide in each dose. More water means you draw more units for the same dose, which makes small doses easier to measure.
How often should I administer my peptide?
It depends on the specific peptide and its half-life. Some are dosed several times a day, others once daily or weekly. Follow the schedule your prescriber or the manufacturer specifies rather than a generic rule.
What should I do if I miss a dose?
Follow the guidance from your healthcare provider or the manufacturer. Generally you either take it when you remember or skip it and resume your normal schedule — you do not double up to make up for a missed dose.
Put it into practice
You don’t have to do any of this by hand. Open the calculator, use the guided step-by-step version if you’re new, reach for the blend calculator for premixed vials, and keep the glossary handy for any term you’re unsure about.