How Much Bacteriostatic Water for a Tirzepatide 10 mg Vial?
A 10 mg vial of tirzepatide reconstituted with 2 mL of bacteriostatic water gives a concentration of 5 mg/mL; with 1 mL it gives 10 mg/mL. A 20 mg vial gives 10 mg/mL with 2 mL and 5 mg/mL with 4 mL. The calculation depends only on the quantity of peptide in the vial and the volume of water added.
View product →There is no single correct volume. Adding more water does not change how much peptide is in the vial. It spreads the same quantity through a larger volume, which changes how many syringe units correspond to a given mass. The tables on this page use 2 mL for a 10 mg vial because it produces round numbers on a U-100 syringe; 1 mL, 3 mL or 5 mL work identically as long as the resulting concentration is written on the vial.
Concentration by water volume
Concentration is peptide mass divided by water volume. A 10 mg vial holds 10 mg whether it receives 1 mL or 5 mL; only the mg/mL figure moves. The right-hand column converts each concentration into the number of U-100 units that contain 1 mg.
| Vial | Bacteriostatic water added | Concentration | Units containing 1 mg |
|---|---|---|---|
| 10 mg tirzepatide | 1 mL | 10 mg/mL | 10 units |
| 10 mg | 2 mL | 5 mg/mL | 20 units |
| 10 mg | 3 mL | 3.33 mg/mL | 30 units |
| 10 mg | 5 mL | 2 mg/mL | 50 units |
| 20 mg tirzepatide | 1 mL | 20 mg/mL | 5 units |
| 20 mg | 2 mL | 10 mg/mL | 10 units |
| 20 mg | 3 mL | 6.67 mg/mL | 15 units |
| 20 mg | 4 mL | 5 mg/mL | 20 units |
Before choosing a larger volume, check that the peptide vial has headspace for it. A 10 mL vial of bacteriostatic water reconstitutes five 10 mg vials at 2 mL each.
Reading the concentration on a U-100 syringe
A U-100 insulin syringe is graduated in units, and 100 units equal 1 mL. Units are therefore millilitres multiplied by 100: 0.1 mL is 10 units and 0.25 mL is 25 units. A 0.5 mL syringe carries 50 units and a 0.3 mL syringe carries 30 units on the same scale, with finer markings that make small volumes easier to read.
To find the volume that contains a given mass, divide the mass by the concentration. At 5 mg/mL (a 10 mg vial with 2 mL of water), the volume that contains 1 mg is 1 divided by 5, which is 0.2 mL, or 20 units. The table below runs the same calculation for four arbitrary amounts. They illustrate the arithmetic and nothing else.
| Mass (illustrative) | Volume at 5 mg/mL | U-100 units |
|---|---|---|
| 0.25 mg | 0.05 mL | 5 units |
| 0.5 mg | 0.1 mL | 10 units |
| 1 mg | 0.2 mL | 20 units |
| 2 mg | 0.4 mL | 40 units |
At 10 mg/mL, which a 10 mg vial gives with 1 mL of water, every volume in the table halves: a 1 mg draw measures 10 units and a 0.5 mg draw measures 5 units. Volumes below about 0.1 mL are hard to read accurately on a 1 mL syringe. Either move to a 0.3 mL or 0.5 mL syringe, or reconstitute with more water so that the same mass occupies a larger, more legible volume.
Tirzepatide is supplied by Vistara Labs as a lyophilised material for research use. The quantities on this page illustrate the arithmetic of dilution and measurement only.
The tirzepatide vial
Tirzepatide is a 39-amino-acid synthetic peptide with a fatty-acid side chain. Vistara Labs supplies it as a 10 mg lyophilised vial; the mass on the label is the peptide in the vial, and the tables above treat it as one quantity. Certificates of analysis are published on the Lab Results page. The same arithmetic covers retatrutide, which is supplied in 10 mg and 20 mg vials.
Tirzepatide as a molecule, and why the vial needs mixing
Tirzepatide is a 39-amino-acid peptide that activates two incretin receptors, GIP and GLP-1. A C20 fatty diacid chain attached through a linker lets it bind albumin in the blood, which stretches its half-life to about five days in human pharmacokinetic studies. As with any peptide, add the water slowly down the vial wall and swirl rather than shake.
The approved medicines built on it, Mounjaro (2022) and Zepbound (2023), are supplied as ready-made solutions in pens and vials; nothing in them needs reconstituting. The research vial is different: a lyophilised powder that has to be made up with bacteriostatic water, which is the only reason the tables on this page exist. Vistara stocks tirzepatide in 10 mg and 20 mg vials, and the 20 mg rows above show that the same water volume simply doubles the concentration. The human trials are summarised in tirzepatide: the human trials, and the buying questions in buying tirzepatide in Canada.
Reconstitution technique
Let the vial reach room temperature, swab both stoppers, and run the measured water slowly down the inside wall of the vial rather than onto the powder. Swirl or tilt gently until the cake dissolves, never shake, and give any remaining powder a few minutes to settle into solution. Label the vial with the date and the concentration, then keep it refrigerated at 2 to 8 °C and protected from light. The full method, with the reason behind each step, is in how to reconstitute peptides with bacteriostatic water.
Why the solution should look clear
Properly reconstituted tirzepatide forms a clear, colourless solution. Cloudiness, strands or a gel that will not disperse usually mean the water went in too fast or the vial was shaken; haze that appears later points to warm or bright storage. The causes are covered in why peptides gel or go cloudy.
Bacteriostatic water, not sterile water
Bacteriostatic water is sterile water with 0.9% benzyl alcohol, a preservative that allows a refrigerated vial to be accessed more than once; plain sterile water is intended for single access. The difference is explained in bacteriostatic water explained.
Frequently asked questions
How much bacteriostatic water do I add to a 10 mg vial of tirzepatide?
There is no single correct volume. With 2 mL of bacteriostatic water a 10 mg vial of tirzepatide gives 5 mg/mL; with 1 mL it gives 10 mg/mL; the 20 mg vial gives 10 mg/mL with 2 mL. Adding more water does not change the quantity in the vial, it spreads it through a larger volume, so write the concentration you chose on the vial.
How many 10 mg vials does a 10 mL vial of bacteriostatic water cover?
A 10 mL vial of bacteriostatic water reconstitutes five 10 mg vials at 2 mL each. Check that the peptide vial has headspace for the volume before choosing a larger one.
How many units on a U-100 syringe contain 1 mg at 5 mg/mL?
At 5 mg/mL (a 10 mg vial with 2 mL of water), the volume that contains 1 mg is 1 divided by 5, which is 0.2 mL, or 20 units. Units are millilitres multiplied by 100, so 0.1 mL is 10 units. The amounts on this page illustrate the arithmetic only.
What should reconstituted tirzepatide look like?
Properly reconstituted tirzepatide forms a clear, colourless solution. Cloudiness, strands or a gel that will not disperse usually mean the water went in too fast or the vial was shaken; haze that appears later points to warm or bright storage. More on the causes in why peptides gel or go cloudy.
Can I use sterile water instead of bacteriostatic water?
Only for a vial that will be accessed once. Bacteriostatic water is sterile water with 0.9% benzyl alcohol, a preservative that allows a refrigerated vial to be accessed more than once; plain sterile water is intended for single access. Details in bacteriostatic water explained.
How should a reconstituted tirzepatide vial be stored?
Refrigerated at 2 to 8 °C, protected from light and labelled with the date and the concentration. Unopened lyophilised vials are kept cold and dark until they are needed. The full storage guide is how to store research peptides.
Work it out for a different vial or concentration
Our peptide calculator opens pre-set for a 10 mg vial with 2 mL of water and marks the 0.5 mg draw of 10 units on a syringe diagram. Change the vial size, water volume, mass or syringe and it recalculates.
Products: Tirzepatide 10 mg and bacteriostatic water 10 mL.
References
Tirzepatide has one of the largest human trial programmes of any compound in this catalogue, including multiple phase 3 trials.
- Tirzepatide Once Weekly for the Treatment of ObesityRandomised phase 3 trial (SURMOUNT-1); 2,539 adults with overweight or obesity without diabetes, 72 weeks.
- Continued Treatment With Tirzepatide for Maintenance of Weight Reduction in Adults With Obesity: The SURMOUNT-4 Randomized Clinical TrialRandomised phase 3 withdrawal trial (SURMOUNT-4); 670 participants randomised after a 36-week open-label phase.
- Tirzepatide for the Treatment of Obstructive Sleep Apnea and ObesityRandomised phase 3 trials in adults with obesity and moderate-to-severe obstructive sleep apnoea (SURMOUNT-OSA).
- Tirzepatide for Heart Failure with Preserved Ejection Fraction and ObesityRandomised phase 3 trial (SUMMIT); 731 patients with obesity-related heart failure with preserved ejection fraction.
- Tirzepatide, cardiovascular outcomes and mortality in obesity and diabetes: a systematic review and meta-analysisSystematic review and meta-analysis; 22 trials, 29,023 participants.
Links open the study record on PubMed so the source can be checked directly. Listing a study is not a claim that its findings apply to any other use, product or route of administration. Research use only.
