How to reconstitute tirzepatide

What is actually in the vial?

The white cake at the bottom of the vial is a carefully engineered molecule, freeze-dried. Tirzepatide is a peptide built on the sequence of GIP, a gut hormone, with a 20-carbon fatty acid fixed to it. That fatty tail lets it ride on albumin, a protein in the blood, which gives it a half-life of about 5 days, so a dose goes in once a week¹. One molecule switches on two receptors at once, GIP and GLP-1¹³.

Reconstituting it does one thing: it turns a fixed mass of powder into a liquid you can measure. The water never changes how much tirzepatide is in the vial, only how concentrated it is. A 10 mg vial holds four 2.5 mg doses whether you add 1 mL or 3 mL. What changes is how far you pull the plunger for each one.

Research-grade vials are not FDA-approved products. The FDA notes that products labelled "for research purposes" are not reviewed for safety, effectiveness or quality before they are sold, so the milligrams printed on the vial are the seller's figure⁷. The approved forms, Mounjaro and Zepbound, come already dissolved (see the last section).

How much bacteriostatic water should you add?

There is no single correct volume. The best one is the volume that puts your doses on clean, readable marks of the syringe. Three numbers decide it: the vial's milligrams, the millilitres of water, and the U-100 syringe, where 100 units fill 1 mL⁶.

The simplest rule is 1 mL of water for every 10 mg of powder. That makes 10 mg/mL, where every 10 units on the syringe hold 1 mg. A 2.5 mg dose is then 25 units, 5 mg is 50 units, and 7.5 mg is 75 units, all on numbered or clean marks.

The figures come from one formula, the same one PepVault's calculator uses: units = dose in mcg × water in mL ÷ (vial in mg × 10). For a 10 mg vial with 2 mL and a 2.5 mg dose: 2,500 × 2 ÷ 100 = 50 units, which is 0.5 mL.

Two things to watch. Very small draws are hard to read: a 60 mg vial suits the higher steps, where 10 mg at 20 mg/mL is a clean 50 units. And an odd volume such as 2.5 mL in a 10 mg vial puts 2.5 mg at 62.5 units, between the marks. Pick the water to suit the dose, and the calculator below shows where each choice lands.

How do you mix it without damaging the peptide?

1. Wash your hands and lay out the vial, the bacteriostatic water, a fresh syringe and alcohol swabs.
2. Flip the plastic caps off both vials and wipe each rubber stopper with an alcohol swab, the same step the Zepbound vial instructions use¹.
3. Draw the planned amount of bacteriostatic water into the syringe.
4. Push the needle through the tirzepatide stopper and let the water run slowly down the inside wall of the vial, not straight onto the powder.
5. Swirl the vial in small circles until the powder is gone. Do not shake it: the label of tesamorelin, an approved peptide that is also mixed with bacteriostatic water, says the same, swirl and do not shake⁵.
6. Hold it to the light. It should be clear, with no particles or cloudiness⁴; Lilly's finished tirzepatide is clear and colourless to slightly yellow¹.
7. Write the date and the strength (for example, "10 mg/mL") on the vial.

Bacteriostatic water is sterile water with 0.9% benzyl alcohol (some bottles 1.1%), a preservative that lets a multi-dose bottle be entered more than once⁴. Plain sterile water has no preservative, which is why multi-dose peptide vials are made with the bacteriostatic kind. The opened water bottle has a shelf life of its own: tesamorelin's instructions say to discard bacteriostatic water 28 days after first use⁵.

How do you draw a dose in units?

Wipe the stopper, turn the vial upside down with the needle tip in the liquid, and pull the plunger slightly past your mark. Tap out any air bubbles and push back to the exact line¹. On a U-100 syringe, units are just hundredths of a millilitre: 50 units is 0.5 mL, 25 units is 0.25 mL⁶.

The slips that matter with vials are about units, not mixing. With compounded semaglutide, a GLP-1 cousin, the FDA said dosing errors may have come from confusion between millilitres, milligrams and units, and from people new to drawing from a vial⁶. Three checks catch the usual slips:

• mg and mcg: 2.5 mg is 2,500 mcg. A dose typed in the wrong one is off by a factor of 1,000.
• Units and mL: "50" means 50 units (0.5 mL), never 50 tenths of a millilitre or 5 mL.
• The syringe scale: the formula assumes U-100. A U-40 syringe holds 40 units per mL, so a U-100 count drawn on it is 2.5 times the volume.

What does the approved dosing schedule look like?

The FDA label starts tirzepatide at 2.5 mg once weekly for 4 weeks, then raises it in 2.5 mg steps after at least 4 weeks on each, to a maintenance dose of 5, 10 or 15 mg; 15 mg is the maximum¹. Here is that ramp at its fastest, with the draw at 10 mg/mL as a worked example:

The last two rows show why the water matters. At the higher steps, a stronger mix (20 mg/mL puts 15 mg at 75 units) keeps each dose to one syringe. In SURMOUNT-1, the trial that led to Zepbound, people reached their dose over a 20-week escalation period and lost an average of 15.0%, 19.5% and 20.9% of body weight at 72 weeks on 5, 10 and 15 mg, against 3.1% on placebo².

Each step up is when the stomach notices most. In the trial, the common side effects were gastrointestinal, mostly mild to moderate, and they came mainly during dose escalation². Smaller meals, eating slowly and stopping at the first sign of fullness are the usual ways people settle in.

Commonly reported: very strong appetite suppression and meals ending early, with nausea or tiredness for a day or two after the injection, mostly after dose increases.

This table is the label's schedule, shown so the math has real numbers. It is not a personal plan; the dose and the pace are set with a clinician.

How should you store mixed tirzepatide, and for how long?

Keep it in the fridge at 2–8 °C, in its box or away from light, and never freeze it. Lilly's label gives the same rules for its own tirzepatide: protect it from heat and light, and never use any that has been frozen¹.

How long a mixed research vial lasts is where the published data runs out. We found no published study that measures the stability of research-grade tirzepatide in bacteriostatic water. The water's own label says not to store a reconstituted drug unless that drug's manufacturer says you can⁴, and a research vial has no manufacturer instructions. The closest reference points come from approved products:

• Lilly's multi-dose tirzepatide vial (a finished liquid whose ingredients include benzyl alcohol and phenol) is discarded 30 days after first use or after 4 weekly doses, whichever comes first¹.
• Tesamorelin, a peptide mixed by the patient with bacteriostatic water, is kept at room temperature once mixed and discarded 7 days after mixing⁵.
• The bacteriostatic water bottle itself is discarded 28 days after first use⁵.

Commonly reported: users keep mixed research vials in the fridge and aim to finish each one within about four weeks, choosing the vial size so they do. That is a habit people report, not a measured shelf life.

That is a practical reason to size the vial to your dose: at 2.5 mg a week, a 10 mg vial is used up in four weeks. If the liquid turns cloudy, grows particles or changes colour, it should not be used⁴.

Do Mounjaro and Zepbound pens need mixing?

No. Lilly's tirzepatide is already a liquid. Single-dose pens and vials hold 2.5 to 15 mg in 0.5 mL, and the multi-dose vial and KwikPen hold four doses in 2.4 mL¹. Never add water to them.

Lilly's vials are drawn in millilitres, not by a mixing formula: the label calls for a 1 mL syringe that can measure the 0.5 mL or 0.6 mL dose¹. The single-dose pens and vials live in the fridge but may spend up to a total of 21 days unrefrigerated at up to 30 °C, and are then discarded¹⁸.