Micrograms, milligrams, and units

Three units of measurement come up constantly and mixing them up is the most common beginner mistake. Two of them measure how much peptide you have. The third measures how much liquid is in your syringe.

A milligram (mg) and a microgram (mcg) both measure weight, meaning the actual amount of peptide. There are 1,000 micrograms in 1 milligram, so you could say that a 5 mg vial holds 5,000 mcg. Doses are usually written in mcg because the amounts are so small and 250 mcg is easier to read than 0.25 mg. It goes the other way too, sometimes. 2 mg is easier to read than 2,000 mcg.

A unit is different. A unit measures liquid on an insulin syringe. The barrel is marked from 0 to 100 and 100 units is 1 mL of liquid. You could also say that 1 unit is one hundredth of a mL.

A unit only tells you how much liquid to draw, not how much peptide you are getting. How much peptide sits in each unit depends on how much water you added when you mixed the vial. You could add more water to decrease the concentration of the same peptide, or add less water to increase the concentration. This is why "10 units" is not a dose. Two people can both draw 10 units and get very different amounts because they mixed their vials differently. It is important to never copy someone else's unit count.

Your protocol is written in mg or mcg, which is the real dose and means the same thing for everyone. Your syringe is marked in units, which is only the translation for your particular vial. Turning one into the other is the whole job of reconstitution, which we cover in module 3.