Peptide Dosing 101: The Math, Insulin Syringes, and How to Avoid 10x Dosing Errors

May 3, 2026 · Education

The single most dangerous mistake in peptide use isn’t storage, sterility, or even the wrong compound — it’s a dosing error. Specifically, the 10x error: someone meant 10 units and drew 100. Knowing the math protects you.

Insulin syringe basics

Almost all peptide injections are done with U-100 insulin syringes. The “U-100” matters: it means 100 units = 1 mL.

So the markings on your syringe represent:

• 10 units = 0.1 mL
• 50 units = 0.5 mL
• 100 units = 1.0 mL

This is true for every U-100 insulin syringe regardless of brand.

The universal dosing formula

To convert your desired dose (in mcg or mg) into units on the syringe:

Units = (Desired dose ÷ Concentration per mL) × 100

Worked examples

Example 1: BPC-157 at 250 mcg

You reconstituted a 5 mg vial with 2 mL of bac water = 2.5 mg/mL = 2,500 mcg/mL.

Units = (250 ÷ 2,500) × 100 = 10 units on your insulin syringe.

Example 2: Tirzepatide at 5 mg

You reconstituted a 10 mg vial with 1 mL of bac water = 10 mg/mL.

Units = (5 ÷ 10) × 100 = 50 units.

Example 3: GHK-Cu at 2 mg

You reconstituted a 50 mg vial with 5 mL of bac water = 10 mg/mL.

Units = (2 ÷ 10) × 100 = 20 units.

Example 4: HCG at 500 IU

HCG is dosed in International Units (IU), not mg. A 5,000 IU vial reconstituted with 5 mL bac water = 1,000 IU/mL.

Units = (500 ÷ 1,000) × 100 = 50 units.

The 10x error and how to prevent it

Most 10x errors come from confusion between milligrams and micrograms. There are 1,000 mcg in 1 mg. If your protocol calls for 250 mcg of BPC-157 and you accidentally calculate as if it were 250 mg, you’ll draw 10 times the intended dose.

Three habits that prevent this:

1. Always write down the calculation before drawing. “5 mg vial ÷ 2 mL = 2.5 mg/mL = 2,500 mcg/mL. 250 mcg = 10 units.”
2. Sanity-check against typical dose ranges. If your math says you need 80 units of BPC-157, you’re wrong — typical doses are 5-15 units.
3. Recheck after every reconstitution change. A new vial size means new math.

Microdoses: when units get tiny

Some compounds (Cagrilintide, IGF-1 LR3) are dosed in mcg with very small volumes. If you can’t see the marking, dilute more.

Example: 1 mg IGF-1 LR3 reconstituted with 1 mL bac water = 1,000 mcg/mL. A 30 mcg dose = 3 units — right at the limit of accuracy on most syringes. Reconstitute the same vial with 2 mL instead and 30 mcg = 6 units, much easier to draw.

The “fingerprint” check

Before injecting, hold the syringe up to good light. The plunger should be at a marking that matches your written calculation. If something feels off, stop and recalculate. The 30 seconds you spend rechecking is the cheapest insurance in the protocol.

Disclaimer: Educational content only. Not medical advice. Consult a provider before beginning any protocol.