Glossary
Insulin pen vs vial
Also called Pen vs vial, Injection pen, Autoinjector, Multi-dose vial
A pen is a prefilled cartridge with a dial that sets each dose. A vial holds liquid (or powder to mix) that you draw with a separate syringe.
In more detail
Pens are what branded GLP-1 drugs come in: you dial a fixed dose, attach a pen needle, and inject. There is no mixing and no unit math. Vials need a syringe and, for powders, reconstitution. Compounded and research products usually come as vials.
Pens use pen needles that screw onto the pen; vials use insulin syringes with fixed needles. The needle and the dose markings are different, so habits from one do not carry over to the other.
Why it matters
Moving from a pen to a vial is exactly where dosing errors happen. A "0.25 mg" pen click is not 25 units of anything. Work it out with the reconstitution calculator.
Related terms
- Compounded vs brandedA branded drug is the FDA-approved product from its maker. A compounded drug is mixed by a pharmacy or outsourcing facility and is not FDA approved.
- 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.
- Units vs mg vs mcgMilligrams (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.
- 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.
Peptides where this comes up
Sources
Each source is labeled by where the information comes from. How we label sources
- Reference workInsulin pen(opens in a new tab)
Wikipedia · checked
- RegulatoryFDA alerts health care providers, compounders and patients of dosing errors associated with compounded injectable semaglutide products(opens in a new tab)
FDA · checked
- RegulatoryOzempic (semaglutide) injection prescribing information(opens in a new tab)
FDA (Drugs@FDA) · checked
Updated