mcg, mg and IU: peptide dosing units explained

Most dosing mistakes are not math errors, they are unit errors. Peptides get measured in a few different systems, and mixing them up can be a thousandfold miss. Here is what each one means and how they relate.

Milligrams and micrograms

A milligram, mg and a microgram, mcg, both measure weight, which is how much actual peptide sits in the vial. The one thing to remember is that 1 mg equals 1,000 mcg. So a 250 mcg dose is the same as 0.25 mg. Many peptides are dosed in micrograms simply because the active amounts are tiny, and 250 mcg reads cleaner than 0.25 mg.

International units

An international unit, IU, does not measure weight at all. It measures biological activity, and it is used for only a handful of compounds where that activity has been standardized, such as HGH and HCG. For those a rough conversion exists, for example about 3 IU per mg of HGH, but it varies by product. Most research peptides are not dosed in IU.

Syringe units

This is the one that causes the most confusion. The units marked on an insulin syringe are volume marks, not a dose. On a U-100 syringe, 100 units is 1 mL, so each unit is 0.01 mL. Twenty units is always 0.20 mL, no matter what is dissolved in it. Your dose in weight comes only from combining that volume with the concentration in the vial.

Putting it together

Weight, in mg or mcg, is what you actually want to deliver. Concentration, in mg per mL, is set by how you reconstituted. Volume, in mL, is weight divided by concentration. Syringe units are just that volume times 100. Keep those four straight and the numbers stop being scary.

If you would rather not track it by hand, the calculator takes your vial size, water and target dose and returns the exact volume and unit mark to draw.