Reconstitution math: the error that sends people to the ER

Read this first — the caveat that sits on top of all the math: every calculation below assumes the vial actually contains what the label says, at the amount the label says. In this supply chain, that assumption is often wrong (see sourcing / purity-vs-potency). The math is only ever as true as the label. Correct arithmetic on a mislabeled vial gives you a confident, precise, wrong dose.

Why this page exists

People inject research-grade peptides using insulin syringes marked in "units", dosing a compound measured in milligrams (mg) or micrograms (mcg), after adding a self-chosen volume of bacteriostatic water. Four different units, three conversions, one syringe that doesn't speak any of the units the compound is measured in. That chain is where 5–10× overdoses happen — not from someone deciding to take too much, but from a decimal or a units slip. This page walks the chain so the slip doesn't happen.

The four quantities

  1. Peptide mass in the vial — e.g. a vial labeled "5 mg" (= 5000 mcg). (Assumes the label is true.)

  2. Water you add (reconstitution volume) — you choose this, e.g. 2 mL of bacteriostatic water.

  3. Resulting concentration — mass ÷ volume. 5000 mcg ÷ 2 mL = 2500 mcg per mL.

  4. What one "unit" on an insulin syringe is — an insulin syringe is marked so that 100 units = 1 mL. So 1 unit = 0.01 mL.

The one conversion people get wrong

Concentration is per mL, but the syringe is in units, and 1 unit = 1/100 mL. So:

mcg per unit = (concentration in mcg/mL) ÷ 100

Worked through with the numbers above: 2500 mcg/mL ÷ 100 = 25 mcg per unit. So on that vial reconstituted that way, "10 units" on the syringe = 250 mcg.

Change the water volume and every number moves. Same 5 mg vial with 1 mL of water instead of 2 mL → 5000 mcg/mL → 50 mcg per unit → "10 units" is now 500 mcg — double. The syringe markings didn't change; the concentration did. This is the trap: people copy a "units" number from someone who reconstituted with a different volume.

Where the 10× errors actually come from

  • mg vs mcg: treating a vial as "5 mcg" when it's "5 mg" (or vice-versa) — a 1000× class error.

  • Volume assumption: copying someone's "units" dose without matching their reconstitution volume (the example above).

  • Syringe type: not all insulin syringes are the same total volume (0.3 / 0.5 / 1.0 mL); "units" are consistent (100/mL) but people misread partial-fill syringes.

  • Reading the barrel: dosing to the wrong graduation on a small barrel.

How to not become the example

  • Do the arithmetic yourself, twice, from the mass and volume — never inherit a "units" number. A units figure is meaningless without the concentration behind it.

  • Write the concentration on the vial once reconstituted (mcg/mL and mcg/unit).

  • Re-derive if you change water volume, vial size, or syringe.

  • Sanity-check against the mass: total units drawn over the vial's life shouldn't exceed the labeled mass. If your math implies you're pulling more drug out than went in, the math is wrong.

  • And re-read the top of this page: none of this protects you if the vial is mislabeled. The arithmetic is necessary, not sufficient.


Substrate is an independent educational harm-reduction resource. It is not medical, legal, or regulatory advice, and it is not a substitute for a licensed clinician. Compounds discussed are largely unapproved in Canada; nothing here endorses their use. Confirm anything health-related with a qualified professional. Built by a medical-sciences student — not a seller and not a clinic.