Issue 02 — What a 'Unit' Actually Means

Last week we promised to demystify the insulin syringe, because it's the tool almost everyone reaches for and almost no one reads correctly. As always, this is educational only — not medical advice, and not a recommendation to use anything. Let's clear up the single most misunderstood word in the whole hobby: "unit."

A unit is volume, not peptide#

Here's the fact that fixes most of the confusion: on a standard U-100 insulin syringe, a "unit" is a measure of volume. Specifically, 100 units = 1 mL, so one unit = 0.01 mL. That's all a unit is. The syringe was designed for insulin, and the markings simply tell you how much liquid you've drawn — not how much of any particular substance is in it.

This is why "I took 10 units" tells you almost nothing on its own. Ten units is 0.1 mL of liquid. How much peptide is in that 0.1 mL depends entirely on the concentration you mixed in Issue 01. Two people can both draw "10 units" and be measuring wildly different amounts of peptide because they reconstituted at different concentrations. The unit is the cup; the concentration is how strong the drink is.

Putting it together#

Take last week's example: a 5 mg vial in 2 mL of bacteriostatic water gave us 25 mcg per unit. So on that specific vial, 10 units = 250 mcg. Change the water volume and that same "10 units" becomes a different amount of peptide. The syringe markings never change — your concentration does. We lay out the full unit-to-mL conversions in our insulin syringe units guide.

One more thing worth a glance: confirm your syringe is U-100, not U-40. They use different scales, and reading one as the other introduces real measurement error. The barrel printing tells you which you have.

Next week#

In Issue 03 we'll cover storage and handling — the cold chain, why you never freeze a reconstituted vial, and how to tell at a glance when a solution has gone off. Small habits, big difference. And the standing reminder: whether to use any substance, and how much, is a decision for a licensed clinician who knows your history. See you in Issue 03.