What tirzepatide is
Tirzepatide is the drug in Mounjaro and Zepbound. Their labels call it "a GIP receptor and GLP-1 receptor agonist" and give its molecular weight as 4813.53 Da.
The approved products are ready-made liquids. Both labels describe a "clear, colorless to slightly yellow solution in pre-filled single-dose pens, single-dose vials, multi-dose vials, or single-patient-use KwikPens". Neither label mentions a powder, or a step for mixing one with water.
The labels measure their vials in millilitres. Both say to instruct patients using vials "to use a syringe appropriate for dose administration (e.g., a 1 mL syringe capable of measuring a 0.5 mL or 0.6 mL dose)". Neither label mentions an insulin syringe. This calculator shows every answer in mL as well as in units.
Where it stands with the FDA
Tirzepatide is FDA-approved in two products from Eli Lilly and Company, Mounjaro and Zepbound. Both labels give the initial U.S. approval as 2022.
The Mounjaro label says it's indicated "as an adjunct to diet and exercise to improve glycemic control in adults and pediatric patients 10 years of age and older with type 2 diabetes mellitus", and to reduce the risk of major adverse cardiovascular events in adults with type 2 diabetes mellitus who are at high risk for these events. The Zepbound label says it's indicated, in combination with a reduced-calorie diet and increased physical activity, "to reduce excess body weight and maintain weight reduction long term in adults with obesity or adults with overweight in the presence of at least one weight-related comorbid condition" and "to treat moderate to severe obstructive sleep apnea (OSA) in adults with obesity".
A search of DailyMed, the National Library of Medicine's collection of drug labels, for tirzepatide in October 2026 returned 8 labels. None of their titles mentions a powder.
A compounded vial is not one of the approved products. FDA's page on unapproved GLP-1 drugs, current as of October 1, 2026, says "compounded drugs are not FDA approved. This means the agency does not review compounded drugs for safety, effectiveness or quality before they are marketed." It also says a compounded drug might be appropriate if a patient's medical need cannot be met by an FDA-approved drug, or the FDA-approved drug is not commercially available.
The same page says FDA "is aware of fraudulent compounded semaglutide and tirzepatide marketed in the U.S. that contain false information on the product label". It says the agency is aware of one reported adverse event associated with a product labeled as compounded tirzepatide from a pharmacy that did not actually compound the product.
FDA also says it has warned companies that illegally sold unapproved drugs containing tirzepatide "falsely labeled" as for research purposes or not for human consumption, and that these products "have been sold directly to consumers for human use with dosing instructions". It says they "are of unknown quality and may be harmful" and urges consumers not to purchase them.
As of May 31, 2026, FDA says it had received more than 730 reports of adverse events associated with compounded tirzepatide. It adds that it is not always possible to determine if an adverse event directly resulted from use of the drug, and that adverse events from compounded versions are likely underreported.
What FDA says about dosing
FDA's page has a section on dosing concerns with compounded semaglutide and tirzepatide. It says the agency "has received adverse event reports that may be related to patients prescribed compounded semaglutide or tirzepatide products in doses beyond what is in the FDA-approved drug label. This could mean using more product in a single dose, taking doses more frequently or increasing the amount more quickly (titration schedule)."
It says some of those adverse events are serious, and that some patients reported seeking medical attention for their symptoms, "including nausea, vomiting, diarrhea, abdominal pain and constipation".
The same section reports dosing errors, and it ties those to semaglutide. FDA says it "received multiple reports of adverse events, some requiring hospitalization, that may be related to dosing errors associated with compounded injectable semaglutide products", and that the errors "resulted from patients measuring and self-administering incorrect doses of the drug, and in some cases, health care professionals miscalculating doses of the drug". The page doesn't say the same of tirzepatide.
FDA "encourages patients to talk with their health care provider or compounder about how to measure and administer the intended dose of compounded semaglutide or tirzepatide". This calculator isn't a substitute for that. It shows each answer in syringe units and in mL, with the dose in mcg and mg and the strength it was worked from, so the figures can be checked against what a prescriber or pharmacy wrote down.
Among the warning signs FDA lists for telehealth companies is one that "makes claims such as the compounded drug is the same as an FDA-approved drug".
What the labels say
The Mounjaro and Zepbound labels give dosages for their own products, and both are once weekly. The Zepbound label says "The recommended starting dosage of ZEPBOUND for all indications is 2.5 mg injected subcutaneously once weekly for 4 weeks. The 2.5 mg dosage is for treatment initiation and is not approved as a maintenance dosage." It says "The maximum dosage of ZEPBOUND for all indications is 15 mg injected subcutaneously once weekly."
The Mounjaro label says "The recommended starting dosage of MOUNJARO is 2.5 mg injected subcutaneously once weekly", and that its maximum dosage is "15 mg injected subcutaneously once weekly in adults" and "10 mg injected subcutaneously once weekly in pediatric patients".
On increases, the Zepbound label says "After 4 weeks, increase the dosage to 5 mg injected subcutaneously once weekly", and that the dosage "may be increased in 2.5 mg increments, after at least 4 weeks on the current dose". For weight reduction it says "The recommended maintenance dosage is 5 mg, 10 mg, or 15 mg, injected subcutaneously once weekly", and for obstructive sleep apnea, 10 mg or 15 mg. The Mounjaro label says "If additional glycemic control is needed, increase the dosage in 2.5 mg increments after at least 4 weeks on the current dose."
Those dosages are the labels', for Mounjaro and Zepbound and for the patients those labels cover. Neither label gives a dose for a compounded vial or for a powder mixed with water, and this page doesn't either.
On their own vials, the labels give the volume. Both say each single-dose vial contains a 0.5 mL solution, and that each multi-dose vial contains 2.4 mL of solution, which provides 4 doses, each of them 0.6 mL. The Zepbound label's vial instructions have the plunger brought to the 0.6 mL line for a multi-dose vial. The labels list the multi-dose vials at 4.17 mg/mL, 8.33 mg/mL, 12.5 mg/mL, 16.7 mg/mL, 20.8 mg/mL and 25 mg/mL.
Those printed strengths are rounded. The labels list 10 mg in 2.4 mL as 4.17 mg/mL, and 10 divided by 2.4 is 4.1667. So if you type a label's printed strength into this calculator, the answer can land a fraction of a unit away from 60 units, which is what 0.6 mL comes to on a U-100 syringe. For one of those vials, the volume its label gives is the one that label goes by.
Both labels carry a boxed warning. The Zepbound label says "In rats, tirzepatide causes dose-dependent and treatment-duration-dependent thyroid C-cell tumors at clinically relevant exposures. It is unknown whether ZEPBOUND causes thyroid C-cell tumors, including medullary thyroid carcinoma (MTC), in humans". It says Zepbound is contraindicated in patients with a personal or family history of MTC or with Multiple Endocrine Neoplasia syndrome type 2, and in patients with known serious hypersensitivity to tirzepatide or any of the excipients.
The Zepbound label says its use "has been associated with gastrointestinal adverse reactions, sometimes severe". Its other warnings include acute kidney injury due to volume depletion, acute gallbladder disease, acute pancreatitis, hypersensitivity reactions, hypoglycemia, diabetic retinopathy complications in patients with type 2 diabetes mellitus, and pulmonary aspiration during general anesthesia or deep sedation.
The most common adverse reactions the Zepbound label lists, reported in 5% or more of patients treated, are "nausea, diarrhea, vomiting, constipation, abdominal pain, dyspepsia, injection site reactions, fatigue, hypersensitivity reactions, eructation, hair loss, gastroesophageal reflux disease". The Mounjaro label's list is "nausea, diarrhea, decreased appetite, vomiting, constipation, dyspepsia, and abdominal pain".
The Zepbound label says coadministration with other tirzepatide-containing products or with any GLP-1 receptor agonist is not recommended. On pregnancy it says "May cause fetal harm. When pregnancy is recognized, discontinue ZEPBOUND." It says to advise females using oral contraceptives to switch to a non-oral contraceptive method, or add a barrier method, for 4 weeks after initiation and for 4 weeks after each dose escalation. It says safety and effectiveness "have not been established in pediatric patients".
On overdose, the Zepbound label says to contact the Poison Help Line or a medical toxicologist, and that "A period of observation and treatment for these symptoms may be necessary, taking into account the half-life of tirzepatide of approximately 5 days."
Storing tirzepatide
The labels' storage instructions are for Lilly's own vials and pens. Both say not to freeze the product, to protect it from heat and light, and to store single-dose vials and unopened multi-dose vials in a refrigerator at 2°C to 8°C (36°F to 46°F). They say a single-dose vial can be stored unrefrigerated at temperatures not to exceed 30°C (86°F) for up to a total of 21 days, and that an unopened multi-dose vial stored at room temperature is thrown away after 30 days.
For an opened multi-dose vial, both labels say to throw it away "after a total of 30 days at room temperature, 30 days after first use, or after taking 4 weekly doses, even if there is medicine left in it".
For compounded vials, FDA says that generally it "recommends that vials containing multiple doses of sterile medications be used within 28 days after the first use because there is an increased risk of contamination after 28 days". It recommends discarding the vial within 28 days after the first use even if medication remains, and always using a new, sterile needle and syringe for each dose. It says not to continue using medication from the vial after 28 days, "even if instructions from the compounder say the medication can be used for longer than 28 days".
FDA also says injectable GLP-1 drugs require refrigeration as indicated in their package inserts, and that it has received complaints of certain compounded GLP-1 drugs arriving warm or with inadequate ice packs. It "recommends patients not use any injectable GLP-1 drug that arrives warm or with insufficient refrigeration".
The Mounjaro and Zepbound labels have no mixing step, so they don't say how long tirzepatide powder mixed with water keeps. FDA's page doesn't either.
Tirzepatide dosage calculator questions
How do I turn a tirzepatide dose into syringe units?
Divide the dose by the concentration to get millilitres, then multiply by 100. A 5 mg vial mixed with 2.5 mL is 2 mg/mL, so one unit on an insulin syringe holds 20 mcg and ten units hold 200 mcg.
How much bacteriostatic water goes in a 5 mg vial of tirzepatide?
There's no single right amount. The water only sets the concentration, and the amount of tirzepatide in the vial stays the same. With 5 mg, 1 mL makes 5 mg/mL, 2 mL makes 2.5 mg/mL and 3 mL makes 1.667 mg/mL. Choose the amount that puts your dose somewhere between about 10 and 40 units, where it's easiest to read.
What if my tirzepatide is already a liquid?
Choose the liquid option and enter the strength printed on the vial, in mg per mL. There's no mixing step, so the volume is the dose divided by that strength, and the units are that volume times 100. At 1 mg/mL, one unit holds 10 mcg and ten units hold 100 mcg. Double the strength and every mark holds double.
Is tirzepatide approved by the FDA?
Yes, as Mounjaro and Zepbound, which are ready-made liquids in pens and vials from Eli Lilly and Company. Both labels give the initial U.S. approval as 2022. A compounded vial isn't one of those products. FDA says compounded drugs are not FDA approved.
Does this page tell me how much tirzepatide to take?
No. The Mounjaro and Zepbound labels give dosages for their own products, and this page reports them as what the labels say and nothing more. The dose box starts empty, and the chart only converts.
Can I use this calculator for a Mounjaro or Zepbound vial?
The arithmetic works for any liquid with its strength on the label, and those vials are liquids. But their labels already give the volume: a single-dose vial contains a 0.5 mL solution, and a multi-dose vial holds 4 doses of 0.6 mL each. The labels speak in mL and call for a syringe appropriate for dose administration, and they say to train patients on proper injection technique first. The label is what to follow.
Can I use it for a Mounjaro or Zepbound pen?
No. A pen isn't drawn into a syringe, so there's nothing to convert.
Is compounded tirzepatide the same as Zepbound?
FDA says compounded drugs are not FDA approved, and that the agency does not review them for safety, effectiveness or quality before they are marketed. Among its warning signs for telehealth companies is one that "makes claims such as the compounded drug is the same as an FDA-approved drug".
Why can't I copy a number of units from someone else?
A unit is a volume, one hundredth of a mL on a U-100 syringe. How much tirzepatide that volume holds depends on the strength of the liquid. The multi-dose vials on the Mounjaro and Zepbound labels alone run from 4.17 mg/mL to 25 mg/mL, so the same number of units can be a very different amount.
More peptide calculators by name
The same instrument, set up one peptide at a time. For any other vial, use the peptide reconstitution calculator.