Reconstitution & Dosing Math

The #1 dangerous mistake

Mixing up micrograms (mcg) and milligrams (mg) — a 1000× error — is the most common and most dangerous beginner mistake. Using the wrong concentration chart for your vial can cause a large overdose. 1 mg = 1000 mcg. Always know which unit your target dose is written in before you draw anything.

Educational only — not medical advice. See Disclaimer.

This is the single most error-prone step for newcomers. The math itself is simple arithmetic, but a misplaced decimal point or a swapped unit can change a dose by 10× or 1000×. Work slowly, write the numbers down, and check them twice.

What “reconstitution” means

Most research peptides ship as a lyophilized (freeze-dried) powder inside a sealed vial. The powder is stable in this form but cannot be drawn into a syringe. Reconstitution is the process of adding a liquid (a “diluent” or “solvent”) to dissolve the powder into a solution you can measure and draw.

The two numbers that matter are:

1. How much peptide is in the vial (the labeled amount, in mg).
2. How much liquid you add (in mL).

Together these fix the concentration — how much peptide sits in each unit of volume. Everything downstream depends on getting these two numbers right.

Bacteriostatic vs. sterile water

	Bacteriostatic water (BAC)	Sterile water
Contains	Sterile water + ~0.9% benzyl alcohol (a preservative)	Sterile water only, no preservative
Multi-use?	Yes — the benzyl alcohol inhibits bacterial growth after the vial is first punctured	No — once opened, it offers no protection against contamination
Typical use	The usual default when a reconstituted vial will be used over several days/weeks	Single-session use, or when a preservative must be avoided
Shelf life after first puncture	Commonly cited as up to ~28 days refrigerated	Not protected once breached

Why BAC is the common default

Because most users dose a vial gradually over days or weeks, the preservative in bacteriostatic water is what allows the reconstituted solution to be re-entered with a needle multiple times. The small amount of benzyl alcohol is generally described as not interfering with peptide structure. Benzyl alcohol is not appropriate for everyone (e.g. it is contraindicated for neonates and may matter in pregnancy) — this is a question for a clinician, not a forum.

See Storage & Handling for how long a reconstituted vial lasts and how to store it.

The math, step by step

Step 1 — Concentration

$\text{Concentration (mg/mL)}=\frac{\text{peptide in vial (mg)}}{\text{water added (mL)}}$

You choose how much water to add. Adding less water makes a more concentrated solution (smaller draw volumes); adding more water makes a dilute solution (larger, easier-to-measure draw volumes). The peptide amount is fixed by the vial; only the water is your choice.

Step 2 — Convert your concentration to per-mcg terms

Because doses are usually in micrograms, convert:

$\text{mcg per mL}=\text{mg/mL}\times 1000$

Step 3 — Volume needed for your dose

$\text{Volume (mL)}=\frac{\text{desired dose (mcg)}}{\text{mcg per mL}}$

Step 4 — Convert volume to “units” on a U-100 insulin syringe

By convention, a U-100 insulin syringe is marked so that 1 mL = 100 units. Therefore:

$\text{Units}=\text{Volume (mL)}\times 100$

So 0.1 mL = 10 units, and the smallest tick (0.01 mL = 1 unit) is the finest division most insulin syringes offer. If your calculated dose lands between ticks, you cannot measure it precisely on that syringe — that is a signal to reconstitute at a different concentration.

Pick a concentration that gives clean numbers

The whole point of choosing your water volume is to land doses on round numbers of units. A dose that comes out to “23.5 units” is hard to draw accurately; re-pick your water amount so the same dose lands on, say, 20 or 25 units.

Fully worked examples

Example 1 — BPC-157, 5 mg vial, 250 mcg dose

• Vial: 5 mg. Water added: 2 mL.
• Step 1 — concentration: 5 mg ÷ 2 mL = 2.5 mg/mL.
• Step 2 — per mL: 2.5 × 1000 = 2500 mcg/mL.
• Step 3 — volume for 250 mcg: 250 ÷ 2500 = 0.1 mL.
• Step 4 — units: 0.1 × 100 = 10 units.
• Result: draw to the 10-unit mark. The 5 mg vial holds 5000 mcg total → 5000 ÷ 250 = 20 doses per vial.

Example 2 — 10 mg vial, 500 mcg dose, more dilute mix

• Vial: 10 mg. Water added: 2 mL.
• Step 1: 10 ÷ 2 = 5 mg/mL → 5000 mcg/mL.
• Step 3: 500 ÷ 5000 = 0.1 mL.
• Step 4: 0.1 × 100 = 10 units.
• Result: draw to 10 units for 500 mcg. Note how a different vial size and dose still landed on 10 units because the concentration changed — this is why you must redo the math for every new vial.

Example 3 — 2 mg vial, 100 mcg dose

• Vial: 2 mg. Water added: 1 mL.
• Step 1: 2 ÷ 1 = 2 mg/mL → 2000 mcg/mL.
• Step 3: 100 ÷ 2000 = 0.05 mL.
• Step 4: 0.05 × 100 = 5 units.
• Result: draw to the 5-unit mark for 100 mcg. The 2 mg vial = 2000 mcg → 20 doses.

Concentration reference table

Volume (mL) per dose, then units on a U-100 syringe, for a common setup. This table assumes the exact vial size and water volume in each row — it is not valid for any other combination.

Vial	Water added	Concentration	100 mcg	250 mcg	500 mcg	1000 mcg (1 mg)
5 mg	2 mL	2.5 mg/mL	4 u (0.04 mL)	10 u (0.10 mL)	20 u (0.20 mL)	40 u (0.40 mL)
5 mg	1 mL	5 mg/mL	2 u (0.02 mL)	5 u (0.05 mL)	10 u (0.10 mL)	20 u (0.20 mL)
10 mg	2 mL	5 mg/mL	2 u (0.02 mL)	5 u (0.05 mL)	10 u (0.10 mL)	20 u (0.20 mL)
10 mg	1 mL	10 mg/mL	1 u (0.01 mL)	2.5 u (0.025 mL)	5 u (0.05 mL)	10 u (0.10 mL)
2 mg	1 mL	2 mg/mL	5 u (0.05 mL)	12.5 u (0.125 mL)	25 u (0.25 mL)	50 u (0.50 mL)

Read the table the right way

Each row is tied to both its vial size and its water amount. If you used a different vial or added a different amount of water, none of these numbers apply — do the four-step math yourself. Reaching for the wrong row is exactly how the 1000× error happens.

Practical reconstitution steps

1. Let the cold vial and the BAC water reach room temperature; wipe both rubber stoppers with a fresh alcohol swab.
2. Draw your chosen volume of bacteriostatic water into a syringe.
3. Inject the water slowly down the inside wall of the peptide vial — aim the stream at the glass, not directly onto the powder.
4. Do not shake. Swirl gently or let it sit; most peptides dissolve in a few minutes. Shaking can damage some peptides and creates foam.
5. Once fully clear, label the vial with the date and concentration, and refrigerate per Storage & Handling.

Sanity-check every dose

Before injecting, ask: Is my dose in mcg or mg? What concentration did I actually mix? Does my unit number match a worked example or the table? If a calculator and your hand-math disagree, stop and find out why. See How Reconstitution Calculators Work for what these tools are actually computing, and How Dosing Calculators Work for the dosing side.

Related

• How Reconstitution Calculators Work
• Injection Technique
• Storage & Handling
• Half-Life & Pharmacokinetics

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