The single most common source of confusion in peptide dosing is that a dose written in milligrams does not translate to a fixed number of units on an insulin syringe. The syringe measures volume, not mass. The number of units you draw depends entirely on how much bacteriostatic water went into the vial.
Concentration equals the peptide mass in the vial divided by the volume of bacteriostatic water you add. A 5 mg vial reconstituted with 2 mL of water gives 2.5 mg per mL. The same 5 mg vial reconstituted with 1 mL gives 5 mg per mL. A 0.5 mg dose is 0.2 mL from the first vial and 0.1 mL from the second. On a U-100 insulin syringe, where 100 units equals 1 mL, that is 20 units versus 10 units for an identical dose. Working this out by hand every time invites arithmetic slips, which is exactly what a peptide reconstitution calculator is for.
Semaglutide has a half-life around one week, which is why weekly administration keeps blood levels relatively flat. Tirzepatide is broadly similar at roughly five days. The practical consequence is that a missed day matters less than it would for a short-acting compound, but it also means a titration step-up takes several weeks to reach a new steady state. Stepping up before that happens is how people end up mistaking accumulation for a dose that was too high from the start.
Vial lot and reconstitution volume, the resulting concentration, dose in milligrams, injection site, date and time. Site rotation matters: alternating abdominal quadrants and thighs avoids repeated trauma to one area. A GLP-1 dose tracker that stores the vial concentration alongside each entry means the units-to-milligrams conversion is never recomputed from memory.
The Peptide Tracker & Calculator is a free iPhone app that keeps the vial maths and the log in one place. Nothing here is medical advice; dosing decisions belong with your prescriber.
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