Tirzepatide 20 mg reconstitution calculator

Zepbound and Mounjaro both come as a 20 mg/2.4 mL multi-dose vial or KwikPen (8.33 mg/mL), which holds four 5 mg doses of 0.6 mL (Zepbound label, Mounjaro label). Every labeled tirzepatide product is a ready-made liquid, and no label mentions adding bacteriostatic water. If your vial reads “20 mg/2.4 mL”, don’t add any: extra liquid would dilute it, and 0.6 mL would no longer hold the labeled amount. A 20 mg vial of powder is compounded or unapproved, and compounded drugs aren’t FDA-approved (FDA).

Mixed with 2.5 mL, a 20 mg vial is 8 mg/mL, or 0.08 mg per unit. That looks almost like the labeled 20 mg/2.4 mL vial, which is printed as 8.33 mg/mL because it holds 5 mg in every 0.6 mL (Zepbound label). The gap matters: 0.6 mL of the 8 mg/mL mix holds 4.8 mg, not 5 mg. With 2 mL the mix is 10 mg/mL (0.1 mg per unit) and with 1 mL it’s 20 mg/mL (0.2 mg per unit), so no common mix matches the labeled vial. A volume or unit count from a labeled vial doesn’t carry over to a mixed one. Work it out from the mg your prescriber gave you and the strength you actually made.

In an alert about compounded semaglutide, the FDA said instructions given in “units”, whose volume varies with the concentration, and confusion between milliliters, milligrams and units may have contributed to dosing errors (FDA alert). For compounded semaglutide or tirzepatide, the FDA encourages patients to ask their health care provider or compounder how to measure and give the intended dose. It also warns of fraudulent compounded tirzepatide with false information on the label (FDA). This calculator can only work from the mg and water you enter. If your instructions give units only, ask the pharmacist which strength they assume.