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How-to · reconstitution
Put 3 mL of bacteriostatic water into the 30 mg Tirzepatide vial. That makes 10.00 mg/mL. A 2.5 mg dose is then 25.0 units on a U-100 syringe.
That volume is the one that lands the draw on a syringe line, so the reading can be checked by eye. More water makes a weaker mix and a bigger draw. Less water makes a stronger mix and a smaller one. The amount of Tirzepatide in the glass never changes. Only the number of marks it takes does.
Tirzepatide is the drug in Zepbound and Mounjaro. It works on two gut hormone signals involved in appetite and blood sugar.
| Water added | Concentration | Per U-100 unit | Example: 2.5 mg = |
|---|---|---|---|
| 1 mL | 30.00 mg/mL | 300 mcg | 8.3 units |
| 2 mL | 15.00 mg/mL | 150 mcg | 16.7 units |
| 3 mL | 10.00 mg/mL | 100 mcg | 25.0 units |
Straight arithmetic: concentration = 30 mg ÷ water, and 1 U-100 unit = 0.01 mL. The example column shows the math at 2.5 mg; it is not a dose recommendation.
Which volume to use is a practical choice rather than a dose. Pick the one that puts your draw somewhere you can actually read it on the syringe. The flags in the last column mark where that fails. “Hard to measure” means the draw is too small to judge by eye. “Won’t fit” means it is bigger than one U-100 syringe holds.
The table above uses one worked example. These are the published quantities, converted into marks on a U-100 barrel at each water volume for a 30 mg vial. Where a quantity was never studied by injection, the row says so.
2.5 mg once weekly for 4 weeks, under the skin.
| Water added | Concentration | Draw |
|---|---|---|
| 1 mL | 30.00 mg/mL | 8.3 units |
| 2 mL | 15.00 mg/mL | 16.7 units |
| 3 mL | 10.00 mg/mL | 25.0 units |
FDA labelZepbound (tirzepatide) — FDA-approved Prescribing Information · retrieved 2026-07-22
5–15 mg once weekly, under the skin. (5, 10, or 15 mg).
| Water added | Concentration | Draw, low to high |
|---|---|---|
| 1 mL | 30.00 mg/mL | 16.7 to 50.0 units |
| 2 mL | 15.00 mg/mL | 33.3 to 100.0 units |
| 3 mL | 10.00 mg/mL | 50.0 to 150.0 unitswon’t fit |
FDA labelZepbound (tirzepatide) — FDA-approved Prescribing Information · retrieved 2026-07-22
At the worked amount, the vial contains twelve doses while the stated storage window covers four. About two thirds would remain, making the larger vial costlier per usable dose in this example.
Buying by the milligram looks like a saving, and on an unmixed vial it is. Once mixed, most of this one expires unused, so the price per dose you can actually draw is far above the price per milligram.
A vial this size only pays if each dose is large enough to empty it inside the window. At the schedule’s opening amount, it is not close.
With the least water, this vial makes a very concentrated solution and the worked dose uses only a few syringe units. Only the largest water amount lands exactly on a syringe line.
Small draw and no mark to stop at is the combination that produces the errors, which is why the flags in the table exist.
Paired with the highest maintenance step, this vial holds two doses and clears the window comfortably. The wastage disappears entirely.
The vial is not wrong. Pairing it with an opening amount is, and nothing on the vial tells you that.
The table shows the offered water volumes. The calculator does the same arithmetic for any volume and any syringe, and shows its working line by line.
Open the Tirzepatide calculator →The arithmetic on this page is only half the question. These are the pages that carry the other half.