Tirzepatide Reconstitution Calculator

Mixing Tirzepatide: What to Know Before You Reconstitute

1. 01

   Why the arithmetic carries more weight here

   FDA has received adverse event reports, some requiring hospitalization, that may relate to dosing errors with compounded injectable GLP-1 products, including patients measuring incorrect amounts and health care professionals miscalculating them. As of 31 May 2026 the agency had received more than 730 adverse event reports associated with compounded tirzepatide. The milligrams-to-units conversion is where that error occurs, and it is the one step this calculator exists to remove.

2. 02

   Check what is in the vial before you add anything

   A lyophilized vial holds a dry cake or film and needs liquid. A vial of solution is already liquid and carries a strength per millilitre on the label. If yours is solution, do not reconstitute it: read the printed mg/mL and the only remaining conversion is millilitres to syringe units.

   The approved multi-dose vial concentrations, from the current label, are:

   Product	Presentation	Strength per mL
   Mounjaro	Multi-dose vial, 10 mg/2.4 mL	4.17 mg/mL
   Mounjaro	Multi-dose vial, 20 mg/2.4 mL	8.33 mg/mL
   Mounjaro	Single-dose pen or vial	Delivers one fixed amount in 0.5 mL

3. 03

   Bacteriostatic water vs. sterile water

   Bacteriostatic water is sterile water with 0.9% benzyl alcohol, a preservative that inhibits bacterial growth once the vial has been punctured. Sterile water carries no preservative and is generally treated as single use. A compounded tirzepatide vial is drawn from weekly across several weeks, so bacteriostatic water is the standard choice.

4. 04

   How much water to add

   Water volume does not change the amount of tirzepatide in the vial. A 10 mg vial holds 10 mg whether you add 1 mL or 2 mL. It changes the concentration, and therefore the size of every draw.

   Vial	Water	Concentration	Per syringe unit
   5 mg	1 mL	5.0 mg/mL	50 mcg
   10 mg	1 mL	10.0 mg/mL	100 mcg
   10 mg	2 mL	5.0 mg/mL	50 mcg
   15 mg	1.5 mL	10.0 mg/mL	100 mcg
   30 mg	3 mL	10.0 mg/mL	100 mcg

   Read the right-hand column. At 10 mg/mL each syringe unit carries 100 mcg, so amounts land on low unit counts and a misread of one or two units is proportionally large. At 5 mg/mL the same amount occupies twice as many units and is correspondingly easier to measure. Enter the amount on your prescription in the calculator above to see the exact count and how full the syringe ends up.

5. 05

   Mixing technique

   Run the water down the inside wall of the vial rather than onto the powder, then let it sit or swirl gently until dissolved. Do not shake. The solution should be clear when fully dissolved, matching the clear to slightly yellow appearance the approved product's label describes.

6. 06

   Storage, and the 28 day rule

   FDA recommends discarding a multi-dose compounded vial within 28 days after first use, even if medication remains, and not continuing past 28 days even if the compounder's instructions permit longer. It also recommends a new sterile needle and syringe for every dose. Injectable GLP-1 drugs require refrigeration as their package inserts state, and FDA recommends not using a product that arrives warm or with inadequate ice packs. Because tirzepatide is a weekly injection, day 28 often arrives with solution still in the vial.

7. 07

   The syringe

   U-100 insulin syringes are standard: 100 units to 1 mL, each unit 0.01 mL. At 10 mg/mL the draws are small enough that the 0.3 mL 30-unit syringe is often the better instrument, because its markings are spaced further apart and a low unit count is easier to read accurately.

8. 08

   Common mistakes worth avoiding

   The recurring ones: adding water to a vial that already contained solution, using the printed strength of an approved multi-dose vial as though it were the concentration of a compounded one, mixing mg and mcg during conversion, reusing a unit count from a vial mixed at a different volume, and running past day 28 because the vial is not empty.