Tirzepatide Dosage Calculator
Work out your tirzepatide reconstitution concentration, draw volume, and syringe units from your vial strength, diluent, and target dose — cross-checked against the FDA-approved Mounjaro/Zepbound titration schedule.
Common compounded research vials come in 10 mg, 20 mg, 30 mg, 40 mg, 60 mg, and 100 mg strengths.
2 mL is a common reconstitution volume for a 40 mg vial; some protocols use 1–4 mL depending on the desired concentration.
The FDA-approved titration schedule runs 2.5, 5, 7.5, 10, 12.5, and 15 mg weekly. This field does not recommend a dose — enter the amount your prescriber has specified.
Draw to
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units on your syringe
How tirzepatide reconstitution math works
Compounded tirzepatide ships as a freeze-dried (lyophilized) powder in a multi-dose vial and has to be dissolved in liquid before it can be measured into a syringe. Prefilled Mounjaro and Zepbound pens, by contrast, arrive pre-mixed at a fixed concentration and don’t require this calculation at all. For a vial-and-syringe setup, the strength of the resulting solution depends on exactly two numbers: how many milligrams are in the vial, and how much liquid you added. This is the same underlying formula used across the site’s Peptide Calculator hub, applied here specifically to tirzepatide’s common vial sizes.
volume to draw (mL) = target dose (mg) ÷ concentration (mg/mL)
syringe units = volume to draw (mL) × syringe scale (100 for U-100, 40 for U-40)
Worked example
A 40 mg vial mixed with 2 mL of bacteriostatic water gives a concentration of 20 mg/mL. To reach the standard 2.5 mg starting dose, you’d draw 0.125 mL — which reads as 12.5 units on a U-100 insulin syringe. That single vial holds roughly 16 doses of that size before it’s empty, though most people move up the titration schedule well before finishing a single vial.
FDA-approved tirzepatide titration schedule
Unlike BPC-157 or other unapproved research peptides, tirzepatide has an FDA-approved dosing schedule attached to its two brand-name products, Mounjaro (type 2 diabetes) and Zepbound (chronic weight management). The schedule below reflects the labeling for both products; this calculator converts whatever dose your prescriber has set into a draw volume, it doesn’t select a dose for you.
| Step | Weekly dose | Typical duration | Purpose |
|---|---|---|---|
| Starting dose | 2.5 mg | 4 weeks | Initiation only — allows the GI system to adjust; not intended as a therapeutic maintenance dose |
| Step 2 | 5 mg | 4+ weeks | First maintenance-range dose |
| Step 3 | 7.5 mg | 4+ weeks | Incremental increase if additional response is needed |
| Step 4 | 10 mg | 4+ weeks | Incremental increase if additional response is needed |
| Step 5 | 12.5 mg | 4+ weeks | Incremental increase if additional response is needed |
| Step 6 (maximum) | 15 mg | Maintenance | Highest FDA-approved dose; not every patient needs to reach this level |
The labeling calls for increases of 2.5 mg at intervals of at least 4 weeks, based on individual tolerability and treatment response, and not every patient needs to reach the 15 mg ceiling to see meaningful results. Dose changes, including how quickly to titrate or whether to hold at a lower step, are a decision for the prescribing clinician, not something this calculator determines.
Tirzepatide’s legal and compounding status in 2026
Brand-name tirzepatide is fully FDA-approved, but the compounded (non-brand) version has gone through a significant regulatory shift since 2024, and a lot of older guides online are now out of date. Here’s the sequence of events as they’ve actually unfolded.
2022–2024
Demand for Mounjaro and Zepbound outpaced manufacturing supply, placing tirzepatide on the FDA’s official drug shortage list. While a brand-name drug sits on that list, licensed 503A and 503B pharmacies are permitted to compound versions of it to fill the supply gap.
Oct–Dec 2024
The FDA declared the tirzepatide shortage resolved, first in early October and then reaffirmed in December 2024. That declaration removed the shortage-based legal basis that had allowed 503B facilities to mass-produce compounded copies.
2025
With the shortage exemption gone, 503A pharmacies narrowed their compounding to patient-specific prescriptions supported by a documented clinical reason the commercial product can’t meet — such as a verified allergy to an inactive ingredient — rather than compounding for cost or convenience alone.
April 30, 2026
The FDA proposed removing tirzepatide, along with semaglutide and liraglutide, from the 503B Bulks List altogether — a move that would close off even the narrow bulk-compounding pathway that remained.
Current status
Brand-name Mounjaro and Zepbound remain fully FDA-approved and widely available through retail pharmacies. Compounded tirzepatide exists in a narrowing regulatory gray zone: it’s not automatically prohibited, but it’s now limited to documented patient-specific medical necessity under state pharmacy law, and enforcement varies by state and by pharmacy.
This status can shift again as the FDA’s proposed 503B Bulks List changes move through the rulemaking process, so treat any claim about compounded tirzepatide’s legality as time-stamped, and verify current status directly with the FDA’s 503A Bulks List page or a licensed pharmacist before relying on it.
Mechanism, briefly
Tirzepatide is a synthetic 39-amino-acid peptide that acts as a dual agonist at both the GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1) receptors, which distinguishes it from single-target GLP-1 agonists like semaglutide. Activating both receptor pathways together slows gastric emptying, increases feelings of fullness, and improves glucose-dependent insulin secretion from the pancreas while suppressing glucagon release, which is why it’s approved for both type 2 diabetes management and chronic weight management. Its long elimination half-life, roughly five days, is what supports a once-weekly injection schedule rather than daily dosing.
Mounjaro vs. Zepbound: what’s the difference?
Both products contain the identical active ingredient, tirzepatide, manufactured by Eli Lilly, and both use the same auto-injector pen hardware and dose strengths. The difference is purely regulatory: Mounjaro is approved for improving blood sugar control in adults with type 2 diabetes, while Zepbound is approved for chronic weight management in adults with obesity, or overweight with at least one weight-related condition, and for moderate-to-severe obstructive sleep apnea in adults with obesity. A prescriber may prescribe either product off-label for the other’s indication, and insurance coverage rules typically follow the on-label indication rather than the drug name itself.
Storage and stability after reconstitution
Prefilled Mounjaro and Zepbound pens should be refrigerated at 36°F–46°F (2°C–8°C) until first use, and can generally be kept at room temperature, up to 86°F (30°C), for up to 21 days once in use, per the manufacturer’s labeling — always check the specific pen’s insert, since guidance can vary slightly by presentation. For compounded vials, once reconstituted with bacteriostatic or sterile water, the solution should be refrigerated and protected from light, and is generally treated as good for a limited window measured in weeks rather than months, since peptide stability in solution gradually declines with time and with repeated temperature swings. Avoid shaking the vial vigorously during mixing — gently swirl or roll it instead, as vigorous agitation can denature the peptide.
Commonly reported side effects
The most frequently reported side effects in tirzepatide’s clinical trials were gastrointestinal — nausea, diarrhea, constipation, and vomiting — and these tend to be most noticeable during dose increases, which is part of why the titration schedule moves gradually rather than starting at a maintenance dose. The FDA-approved labeling also carries a boxed warning regarding thyroid C-cell tumors observed in rodent studies; the relevance of this finding to humans hasn’t been established, and tirzepatide is contraindicated in patients with a personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2. This section is a general summary, not a substitute for the full prescribing information or a conversation with your prescriber.
Frequently asked questions
The FDA-approved starting dose for both Mounjaro and Zepbound is 2.5 mg once weekly for 4 weeks. This initiation dose is not intended to be therapeutic on its own — it’s meant to let the digestive system adjust before moving to the 5 mg maintenance-range dose.
Divide your target dose in mg by your solution’s concentration in mg/mL. Concentration itself equals the total tirzepatide in the vial (mg) divided by the diluent volume you added (mL). The calculator above performs both steps and also converts the result to syringe units.
Brand-name tirzepatide (Mounjaro, Zepbound) is fully FDA-approved and legal by prescription. Compounded tirzepatide lost its shortage-based legal justification when the FDA declared the shortage resolved in late 2024, and is now limited to narrow, patient-specific medical-necessity situations under state pharmacy law. The FDA proposed further restricting bulk compounding of tirzepatide in April 2026.
It depends entirely on your reconstitution concentration. For example, a 40 mg vial mixed with 2 mL of water yields 20 mg/mL, so a 5 mg dose would draw to 0.25 mL, or 25 units on a U-100 insulin syringe. Enter your own vial and water numbers above for an exact figure.
Semaglutide (Ozempic, Wegovy) targets only the GLP-1 receptor, while tirzepatide (Mounjaro, Zepbound) is a dual agonist acting on both the GIP and GLP-1 receptors. In head-to-head clinical trial data, tirzepatide has generally produced greater average weight reduction, though individual response varies and the two are dosed on entirely different mg scales.
No — the syringe type only changes how the same liquid volume is displayed. A U-100 and U-40 insulin syringe both hold 1 mL in the barrel; they simply print a different unit scale next to the plunger for that same 1 mL.
No. It performs the arithmetic of concentration and draw volume based on numbers you enter yourself. It doesn’t evaluate, suggest, or validate whether any particular dose, product, or titration pace is appropriate for you — that determination belongs with your prescriber.
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References
- U.S. Food & Drug Administration — Mounjaro (tirzepatide) Prescribing Information. View label
- U.S. Food & Drug Administration — Zepbound (tirzepatide) Prescribing Information. View label
- Frias JP, Davies MJ, Rosenstock J, et al. “Tirzepatide versus Semaglutide Once Weekly in Patients with Type 2 Diabetes.” New England Journal of Medicine, 2021;385:503–515. Read study
- Jastreboff AM, Aronne LJ, Ahmad NN, et al. “Tirzepatide Once Weekly for the Treatment of Obesity.” New England Journal of Medicine, 2022;387:205–216. Read study
- U.S. Food & Drug Administration — 503A Bulks List and drug shortage database