Glossary
Units vs mg vs mcg
Also called Units to mg, mg to units, IU vs units, Micrograms vs milligrams
Milligrams (mg) and micrograms (mcg) measure how much peptide you take. Syringe units measure how much liquid you draw. You need the vial's concentration to convert one into the other.
In more detail
1 mg equals 1,000 mcg. A protocol written as 250 mcg is the same as 0.25 mg. Mixing the two up is a thousandfold error, which is why guides tell you to check the unit twice.
Syringe units on a U-100 syringe are volume: 100 units is 1 mL. They are not International Units (IU). IU is a separate measure of biological activity used for a few products, such as growth hormone, and it does not map to syringe lines.
The conversion: concentration (mg per mL) = mg in the vial divided by mL of water added. Volume to draw (mL) = dose in mg divided by concentration. Syringe units = mL times 100.
Why it matters
The FDA has documented dosing errors with compounded semaglutide where patients and even prescribers mixed up milligrams, milliliters and units, and some patients took 5 to 20 times the intended dose. Our reconstitution calculator does this math for you, and mg to units conversion explains it step by step.
Related terms
- U-100 insulin syringeThe small insulin syringe most people use for peptides. Its scale is marked in units, where 100 units equals 1 mL, so 1 unit is 0.01 mL of liquid.
- ReconstitutionAdding a sterile liquid, usually bacteriostatic water, to a vial of freeze-dried peptide powder so it becomes an injectable solution with a known strength.
- DrawPulling liquid from a vial into a syringe. To draw a dose is to measure the number of units you need on the syringe.
- TitrationStarting at a low dose and raising it in steps over weeks, so the body adapts and side effects stay manageable.
Peptides where this comes up
Sources
Each source is labeled by where the information comes from. How we label sources
- RegulatoryFDA alerts health care providers, compounders and patients of dosing errors associated with compounded injectable semaglutide products(opens in a new tab)
FDA · checked
- Competitor guideSyringe measurement guide(opens in a new tab)
peptidedosages.com · checked
- Reference workSyringe: standard U-100 insulin syringes(opens in a new tab)
Wikipedia · checked
Updated