Understanding peptide units in the research
The single biggest source of confusion in peptide write-ups is that three different unit systems get mixed up. Weight, volume and potency each measure a different thing, and telling them apart is what lets you actually read the dosing figures in a study or on a compound page. This walks through what each one means and how they relate, as background on the research.
The three unit systems
Three systems turn up in the literature, and each measures something different.
Weight: mg and mcg
The mass of peptide. This is what a vial label shows and what a dosing figure is usually stated in. 1 mg is 1,000 mcg, and micrograms are sometimes written µg. Whether a figure means mg or mcg matters, since reading one as the other is a 1,000 fold difference.
Volume: mL and syringe units
How much liquid an amount works out to. On a U-100 insulin syringe, 100 units is 1 mL, so one unit is 0.01 mL, and mL and cc mean the same thing. The key point is that syringe units are volume marks, not international units and not a dose. Twenty units is 0.20 mL of liquid whatever is dissolved in it.
Potency: IU
International units measure biological activity for a few standardized compounds, mainly HGH at about 3 IU per mg, whose IU come from a bioassay. Most peptides do not use IU at all. IU describe potency, and they are a separate thing from the volume marks on a syringe. The two get run together constantly in online write-ups, which is the mistake this page exists to head off.
How concentration ties them together
The link between weight and volume is concentration, and it comes from reconstitution. Concentration is the total peptide divided by the water it was dissolved in. A 5 mg vial in 2 mL of water is 2.5 mg per mL. Once concentration is known, a weight and a volume convert back and forth: a 0.25 mg reference amount is 0.25 divided by 2.5, which is 0.10 mL, and 0.10 mL is the 10 mark on a U-100 syringe. That is the same arithmetic the calculator runs. It is worth understanding as background, not as a step to follow.
Conversion tables
| mg | mcg |
|---|---|
| 0.1 mg | 100 mcg |
| 0.25 mg | 250 mcg |
| 0.5 mg | 500 mcg |
| 1 mg | 1,000 mcg |
| 2 mg | 2,000 mcg |
| 5 mg | 5,000 mcg |
| mL | U-100 units |
|---|---|
| 0.01 mL | 1 unit |
| 0.05 mL | 5 units |
| 0.10 mL | 10 units |
| 0.20 mL | 20 units |
| 0.25 mL | 25 units |
| 0.50 mL | 50 units |
| 1.00 mL | 100 units |
Where write-ups go wrong
Two mix-ups account for most of the confusion you will see online.
- Treating IU as a syringe mark. IU are potency, and a syringe unit is volume, so the number of units an IU amount works out to depends entirely on the concentration. This is why the same IU figure maps to different marks at different water volumes.
- Treating mg and mcg as interchangeable. They differ by a factor of 1,000, so 250 mcg and 250 mg are not remotely the same amount. When a figure is unlabeled, the surrounding context is the only way to tell which was meant.