# Compounded semaglutide and tirzepatide units: how the mg on your prescription becomes units on the syringe

> Units = dose in mg ÷ the vial's mg/mL x 100. Worked examples for compounded semaglutide and tirzepatide, why the label's mg/mL matters, and a calculator.

Source: https://peppytracker.com/guides/compounded-semaglutide-tirzepatide-units/
Last updated: 2026-08-30

Compounded semaglutide and tirzepatide come in vials labelled by concentration (mg per mL) and are drawn with a U-100 insulin syringe, where 100 units is 1 mL. Units = dose in mg ÷ concentration in mg/mL x 100. At 2.5 mg/mL, a 0.25 mg dose is 10 units; at 5 mg/mL it is 5 units. The vial label's concentration is the number that matters. Always verify with your prescriber.

## Why compounded semaglutide units confuse people

Brand pens hide the math. Ozempic, Wegovy, Mounjaro and Zepbound are dosed in milligrams at a concentration fixed by the manufacturer, and the pen dials the dose for you. Compounded semaglutide and tirzepatide come as a multi-dose vial and an insulin syringe, and the instructions say something like "inject 10 units weekly". The prescription says milligrams, the syringe says units, and the number that links them is printed on the pharmacy label as a concentration in mg per mL. Get the concentration wrong and the dose is wrong by the same factor.

This is not a theoretical problem. In July 2024 the FDA issued an alert about dosing errors with compounded injectable semaglutide, describing patients and clinicians who miscalculated the conversion from milligrams to units or millilitres and administered five to ten times the intended dose, some ending up in hospital. The FDA's own summary of the cause: unfamiliarity with drawing from a vial, plus confusion between millilitres, milligrams and "units". The rest of this page is the arithmetic, worked slowly, and how Peppy carries it for you so you check a number instead of recomputing it every week.

## Units, millilitres and milligrams

A U-100 insulin syringe is marked in units, and **100 units = 1 mL**. So one unit is 0.01 mL. Units are a volume, not an amount of drug. How much drug is in that volume depends on the vial's concentration:

**Units to draw = dose (mg) ÷ concentration (mg/mL) x 100**

Two labels that look alike are not: a vial labelled **5 mg/mL** has 5 mg in every millilitre; a vial labelled **5 mg/2 mL** has 5 mg spread over 2 mL, which is 2.5 mg/mL, half as strong per unit. When a label gives total mg and total mL, divide the first by the second before doing anything else.

## Worked examples: semaglutide

These use common concentrations to show the arithmetic. They are not doses; your dose comes from your prescriber, and the concentration comes from your label.

| Vial label | Concentration | Dose | Volume | Units (U-100) |
| --- | --- | --- | --- | --- |
| 2.5 mg/mL | 2.5 mg/mL | 0.25 mg | 0.1 mL | 10 units |
| 2.5 mg/mL | 2.5 mg/mL | 0.5 mg | 0.2 mL | 20 units |
| 2.5 mg/mL | 2.5 mg/mL | 1 mg | 0.4 mL | 40 units |
| 5 mg/2 mL | 2.5 mg/mL | 0.25 mg | 0.1 mL | 10 units |
| 5 mg/mL | 5 mg/mL | 0.25 mg | 0.05 mL | 5 units |
| 5 mg/mL | 5 mg/mL | 1 mg | 0.2 mL | 20 units |

Read the first and fifth rows together. The same 0.25 mg is 10 units from one vial and 5 units from another. If you switch pharmacies, or the same pharmacy sends a different strength, the units change even though the prescription did not. Wegovy's label, for comparison, escalates in mg (0.25, 0.5, 1, 1.7, 2.4 mg); a compounded protocol following a similar mg ladder needs the units recomputed at every step, for the vial in your hand. The [titration tracker guide](https://peppytracker.com/guides/glp-1-titration-schedule-tracker/) covers how step-ups are entered, and the [compounded semaglutide page](https://peppytracker.com/compounds/semaglutide-compounded/) has the catalog entry.

## Worked examples: tirzepatide

Tirzepatide doses are larger in mg, so compounded vials tend to be more concentrated. The arithmetic is identical.

| Vial label | Concentration | Dose | Volume | Units (U-100) |
| --- | --- | --- | --- | --- |
| 10 mg/mL | 10 mg/mL | 2.5 mg | 0.25 mL | 25 units |
| 10 mg/mL | 10 mg/mL | 5 mg | 0.5 mL | 50 units |
| 20 mg/2 mL | 10 mg/mL | 5 mg | 0.5 mL | 50 units |
| 20 mg/mL | 20 mg/mL | 2.5 mg | 0.125 mL | 12.5 units |
| 20 mg/mL | 20 mg/mL | 5 mg | 0.25 mL | 25 units |

The 12.5-unit row is there on purpose. Half-units are hard to read on many insulin syringes, and a result like that is a signal to ask the pharmacy which syringe they intended, not to round on your own.

## Lyophilized vials: you set the concentration

Some compounded products arrive as a powder you reconstitute with bacteriostatic water. Then the concentration is not on the label; it is whatever you make it: **mg in the vial ÷ mL of water added**. A 5 mg vial with 2 mL of water is 2.5 mg/mL; with 1 mL it is 5 mg/mL, and every dose is half the units. Write the water volume on the vial the day you mix it. The [reconstitution guide](https://peppytracker.com/guides/peptide-reconstitution-units-to-draw/) covers this case in detail, and Peppy's calculator takes vial mg and water mL directly so the concentration step cannot be skipped.

## Peppy is a tracking tool. Dose calculations are mathematical conversions only. Always follow your prescriber's instructions and verify every draw-up yourself.

Three habits that catch most errors: read the mg/mL on the label every time a new vial arrives, not just the first; check that the units on the syringe match the volume you expect (10 units should be a tenth of a 1 mL syringe); and if the number you compute does not match the number the pharmacy told you, stop and call before injecting. Peppy shows the units it computed next to the inputs you gave it so a mismatch is visible, and warns when a draw will not fit the syringe you picked.

## How to do this in Peppy

1. In the **Protocols** tab tap **+**, tap **Choose**, and pick **Compounded Semaglutide** or **Compounded Tirzepatide**. Both are vial compounds with units as the default, on a weekly schedule.
2. In the inline **Calculator**, enter the **Vial** mg and **Water** mL. For a pre-mixed vial labelled 5 mg/2 mL, enter 5 mg and 2 mL; for one labelled 2.5 mg/mL, enter 2.5 mg and 1 mL. Enter your prescribed **Dose** in mg. Peppy shows the concentration and "Draw up N units" with a syringe graphic. Always verify with your prescriber.
3. Set the shot day and time. If your prescriber has given you a step-up plan, enter it under **Dose step-ups** (Pro) and Peppy recomputes the units at each step.
4. Save. The **Today** tab hero shows the next shot and the units to draw; the Next Shot widget (Pro) shows the same.
5. On shot day, tap the dose, tap the suggested site on the body map, and log. Tap the dose field to override the amount if the pharmacy changed the concentration and your units changed with it, then update the protocol.
6. If the calculator says "Doesn't fit a 1 mL syringe", do not split the draw on your own; pick the syringe you actually have from the **Syringe** control and confirm with the pharmacy.

## Frequently asked

### How many units is 0.25 mg of compounded semaglutide?

It depends entirely on the vial's concentration. At 2.5 mg/mL, 0.25 mg is 0.1 mL, which is 10 units on a U-100 syringe. At 5 mg/mL it is 5 units. At 1 mg/mL it is 25 units. Read the mg/mL on your pharmacy label and confirm the number with your prescriber or pharmacist.

### How many units is 2.5 mg of compounded tirzepatide?

At 10 mg/mL, 2.5 mg is 0.25 mL, which is 25 units. At 20 mg/mL it is 12.5 units, and half-units are hard to read on many syringes, which is a reason to ask the pharmacy rather than guess. Use the concentration printed on your vial.

### Why are compounded semaglutide units different from the pen doses?

Ozempic, Wegovy, Mounjaro and Zepbound pens are dosed in mg at fixed concentrations set by the manufacturer. A compounded vial's concentration is chosen by the pharmacy and varies between pharmacies, so the same mg dose is a different number of units from one vial to the next. That is why the FDA has warned about mg-to-units conversion errors.

### What is 5 mg/2 mL as a concentration?

5 mg in 2 mL is 2.5 mg/mL. Some labels give total mg and total mL rather than mg/mL; divide the first by the second. Do not confuse a 5 mg/2 mL vial (2.5 mg/mL) with a 5 mg/mL vial, which is twice as strong per unit.

### Does Peppy tell me my dose?

No. Peppy converts the dose your prescriber gave you into units for the concentration you enter, and shows it on the Today tab and the log sheet. It is a mathematical conversion only. Always follow your prescriber's instructions and verify every draw-up yourself.

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Peppy is a tracking tool, not medical advice. Dose calculations are mathematical conversions only. Always follow your prescriber's instructions and verify every draw-up yourself.

Peppy is a free iPhone app (Pro subscription optional). App Store: https://apps.apple.com/us/app/peptide-tracker-peppy/id6775005514