mg to units: how to convert a peptide dose to syringe units

You need three numbers: how many mg are in the vial, how many mL of water you added, and your dose.

1. Concentration (mg per mL) = mg in the vial divided by mL of water.
2. Volume to draw (mL) = dose in mg divided by concentration.
3. Units on a U-100 syringe = volume in mL times 100.

That is the whole method. There is no fixed answer to "how many units is 5 mg" without knowing how the vial was mixed. The same 2.5 mg dose from a 10 mg vial is 25 units if the vial was mixed with 1 mL and 50 units if it was mixed with 2 mL.

Our reconstitution calculator runs these steps for your exact vial, and it can use your vial's tested amount instead of the label.

1 mg = 1,000 mcg. A dose written as 250 mcg is 0.25 mg. A 5 mg vial holds 5,000 mcg.

Pick one unit and convert everything to it before you divide. Mixing mg and mcg is a thousandfold error, and it is the easiest one to make at the kitchen table.

Divide the vial's mg by the mL of water you added. A 10 mg vial mixed with 2 mL is 5 mg per mL. If you do not know how much water went in, you cannot work out a dose from that vial. That is why the label on the vial should carry the volume and the date.

Divide your dose by the concentration to get mL, then multiply by 100 for U-100 units. Round to the nearest line your syringe actually has: on most 1 mL syringes that is every 2 units, on 0.5 mL and 0.3 mL syringes every unit.

If your dose is only a few units, more water in the next vial or a smaller syringe will make it easier to measure.

These vial and water combinations and doses come from our compound pages; the arithmetic is computed, not estimated.

• BPC-157, 5 mg vial with 2 mL: 2.5 mg per mL. A 250 mcg dose is 0.1 mL, which is 10 units.
• Semaglutide, 5 mg vial with 2 mL: 2.5 mg per mL. A 0.25 mg dose is 0.1 mL, which is 10 units.
• Tirzepatide, 10 mg vial with 1 mL: 10 mg per mL. A 2.5 mg dose is 0.25 mL, which is 25 units.
• Tirzepatide, 10 mg vial with 2 mL: 5 mg per mL. A 2.5 mg dose is 0.5 mL, which is 50 units.

To find how much is in a number of units: units divided by 100 gives mL, and mL times concentration gives mg.

• 10 units from a 5 mg vial mixed with 2 mL (2.5 mg per mL) is 0.25 mg, or 250 mcg.
• 20 units from a 5 mg vial mixed with 2 mL (2.5 mg per mL) is 0.5 mg, or 500 mcg.
• 40 units from a 10 mg vial mixed with 2 mL (5 mg per mL) is 2 mg, or 2,000 mcg.

This is how to answer questions like "20 units is how many mg": the answer depends on the vial's concentration, so start there.

FDA collected reports of people taking 5 to 20 times their intended dose of compounded semaglutide. The causes it named:

• Confusing mL, mg and units. In one case a 0.25 mg dose, which was 5 units at that vial's strength, was prescribed as 25 units. At the same strength, 25 units is 1.25 mg, 5 times the intended dose.
• Syringes much larger than the dose, which makes small volumes hard to measure.
• Different concentrations between products, so a units number from one vial was used on another.

The fix is the same each time: work from your own vial's mg and water, use the smallest syringe that fits, and re-check the math when anything changes. See How to read an insulin syringe.

International Units (IU) measure biological activity, not volume. They are used for a few products such as growth hormone and hCG, where a vial is labeled in IU. Syringe units and IU only line up by coincidence. If a protocol is written in IU, convert it with the IU figure on the vial's label, then work out the volume the same way.