To convert a compounded tirzepatide dose from milligrams to units, divide the dose in mg by the vial concentration in mg/mL, then multiply by 100. For example, a 2.5 mg dose from a 10 mg/mL vial is 0.25 mL, which equals 25 units on a U-100 insulin syringe. The same 2.5 mg dose from a 5 mg/mL vial is 50 units.
Because compounded vials come in different concentrations, the number of units changes from vial to vial even when the dose in mg stays the same. This guide explains the math, gives conversion tables, and covers the dosing errors providers should help patients avoid.
Why Compounded Tirzepatide Is Measured in Units
Brand tirzepatide (Mounjaro and Zepbound) comes in prefilled pens and single-dose vials with a fixed dose. Compounded tirzepatide usually comes in a multi-dose vial, and patients draw each dose with an insulin syringe.
Insulin syringes are marked in units, not milligrams. On a standard U-100 syringe:
- 100 units = 1 mL
- 10 units = 0.1 mL
- 1 unit = 0.01 mL
The units on the syringe measure volume only. How much tirzepatide that volume contains depends on the concentration of the vial.
The Conversion Formula
Use these three steps:
- Find the concentration on the vial label, written in mg/mL.
- Calculate the volume: dose (mg) ÷ concentration (mg/mL) = volume (mL).
- Convert to units: volume (mL) × 100 = units on a U-100 syringe.
Example: The prescribed dose is 5 mg and the vial is 10 mg/mL.
5 ÷ 10 = 0.5 mL. 0.5 × 100 = 50 units.
Tirzepatide mg to Units Conversion Chart
The chart shows units on a U-100 insulin syringe for common doses and concentrations. Always use the concentration printed on the patient’s own vial.
| Dose (mg) | 5 mg/mL vial | 10 mg/mL vial | 20 mg/mL vial |
| 2.5 mg | 50 units (0.50 mL) | 25 units (0.25 mL) | 12.5 units (0.125 mL) |
| 5 mg | 100 units (1.00 mL) | 50 units (0.50 mL) | 25 units (0.25 mL) |
| 7.5 mg | 150 units (1.50 mL) | 75 units (0.75 mL) | 37.5 units (0.375 mL) |
| 10 mg | 200 units (2.00 mL) | 100 units (1.00 mL) | 50 units (0.50 mL) |
| 12.5 mg | 250 units (2.50 mL) | 125 units (1.25 mL) | 62.5 units (0.625 mL) |
| 15 mg | 300 units (3.00 mL) | 150 units (1.50 mL) | 75 units (0.75 mL) |
A standard 1 mL insulin syringe holds 100 units. Doses above 100 units need either a higher concentration or more than one draw, which increases the risk of error. Pharmacies often choose a concentration that keeps each dose under 100 units.
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How Tirzepatide Is Usually Titrated
The FDA-approved labeling for brand tirzepatide for weight management (Zepbound) starts at 2.5 mg once weekly for 4 weeks. The dose then increases in 2.5 mg steps, at least 4 weeks apart. Maintenance doses are 5 mg, 10 mg, or 15 mg once weekly, and the maximum dose is 15 mg weekly.
| Weeks | Weekly dose | Units from a 10 mg/mL vial |
| 1 to 4 | 2.5 mg | 25 units |
| 5 to 8 | 5 mg | 50 units |
| 9 to 12 | 7.5 mg | 75 units |
| 13 to 16 | 10 mg | 100 units |
| 17 to 20 | 12.5 mg | 125 units |
| 21 and after | 15 mg | 150 units |
This table shows the brand label schedule as a reference. The prescriber sets each patient’s dose and schedule, and many patients stay at a lower maintenance dose.Common Dosing Errors With Compounded GLP-1 Injections
The FDA has received reports of patients overdosing on compounded GLP-1 injections, including cases that led to hospitalization. Many errors come from confusion between units, milliliters, and milligrams.
The most common mistakes are:
- Reading mg as units. A patient told “5” draws 5 units instead of 50 units, or 50 units instead of 5 units.
- Reading mL as units. A patient told “0.5” draws 50 units when 5 units was intended, or the reverse.
- Using the old concentration. A refill arrives in a different concentration, but the patient keeps drawing the same number of units.
- Using the wrong syringe. A U-40 or 0.3 mL syringe has different markings from a 1 mL U-100 syringe.
- Double dosing. A patient forgets whether the weekly dose was taken.
How Providers Can Prevent Dosing Errors
- Write the dose three ways on instructions: mg, mL, and units, for example “2.5 mg = 0.25 mL = 25 units.”
- Specify the syringe size and type in the prescription.
- Flag concentration changes whenever a refill uses a different concentration.
- Teach back. Ask patients to show where they will draw to on the syringe.
- Use a dose log so patients record the date and units of each injection.
- Coordinate with the pharmacy so the label, patient instructions, and prescription all match.
For patient education on injections and adherence, see How Compounding Improves Patient Adherence.
Is Compounded Tirzepatide Still Available in 2026?
The FDA removed tirzepatide from its drug shortage list on December 19, 2024. State-licensed 503A pharmacies had until February 18, 2025, and 503B outsourcing facilities until March 19, 2025, to stop compounding copies of the commercial product under the shortage policy.
Since then, federal law generally does not allow pharmacies to routinely compound drugs that are essentially copies of a commercially available product. A 503A pharmacy may compound a patient-specific version only when the prescriber determines that a change produces a clinically significant difference for that patient. Rules continue to change, so confirm current FDA guidance before prescribing. Learn more in FDA Regulation of Peptides and Compounding Pharmacies in 2026 and our 503A compounding pharmacy guide.
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FAQs
How many units is 2.5 mg of compounded tirzepatide?
It depends on the vial concentration. From a 10 mg/mL vial, 2.5 mg is 25 units. From a 5 mg/mL vial, it is 50 units. From a 20 mg/mL vial, it is 12.5 units.
How do you convert tirzepatide mg to units?
Divide the dose in mg by the concentration in mg/mL to get mL, then multiply by 100 to get units on a U-100 insulin syringe.
How many units is 5 mg of tirzepatide?
From a 10 mg/mL vial, 5 mg is 50 units. From a 20 mg/mL vial, it is 25 units.
Why did my units change when the dose stayed the same?
The refill likely came in a different concentration. The units on the syringe measure volume, so a stronger vial needs fewer units for the same mg dose.
What syringe is used for compounded tirzepatide?
Most patients use a U-100 insulin syringe, where 100 units equals 1 mL. The prescriber and pharmacy should specify the syringe size.
Is compounded tirzepatide FDA-approved?
No. Compounded drugs are not FDA-approved. Brand tirzepatide products, Mounjaro and Zepbound, are FDA-approved.
Work With a Pharmacy That Gets the Details Right
Clear labels and matching instructions prevent most dosing errors. Emerald Compounding Pharmacy works with weight management clinics on patient-specific prescriptions, clear labeling, and direct pharmacist support. Learn more about our weight loss compounding pharmacy in Tampa or call (877) 443-7711.
