On every branded tirzepatide single-dose pen and single-dose vial, one weekly dose is 0.5 mL, which reads 50 units on a U-100 syringe, and that is true at all six strengths from 2.5 mg to 15 mg. On the branded multi-dose vial each of the four doses is 0.6 mL, or 60 units. Both figures come from the Mounjaro and Zepbound prescribing information.
For a compounded vial there is no equivalent answer, because a unit measures volume rather than drug. The same 50 units that is a starting dose on one vial is the maximum labelled dose on another. Below is every labelled dose converted at each concentration in circulation, and the one arithmetic mistake that accounts for most of the reported overdoses.
- A U-100 syringe unit is 0.01 mL. It measures volume, so the milligrams it delivers depend on the concentration of the vial it is drawn from.
- Branded single-dose pens and vials hold 2.5 mg to 15 mg in 0.5 mL, so every dose is 50 units. Branded multi-dose vials hold each dose in 0.6 mL, so every dose is 60 units.
- Compounded vials range from roughly 5 mg/mL to 34 mg/mL, so the same dose can be anything from 8 units to 300 units.
- Carrying "50 units" from a branded vial to a 30 mg/mL compounded vial delivers 15 mg instead of 2.5 mg, a six-fold error that sits inside the five to 20-fold range FDA has reported.
Why units has three different answers for tirzepatide
A unit on an insulin syringe is a volume marking. On the U-100 syringes that are standard in the United States, 100 units is 1 mL, so one unit is 0.01 mL. Nothing about that marking knows which drug is in the barrel or how concentrated it is. The full derivation is in our mg to units conversion piece, and this page applies it to tirzepatide alone.
Tirzepatide is supplied in four presentations, and the answer to "how many units" is different in each:
- Single-dose pen: a fixed-dose autoinjector. No syringe, so no units.
- Single-dose vial: the dose sits in 0.5 mL at every strength, so 50 units.
- Multi-dose vial: four doses per vial, each 0.6 mL, so 60 units.
- Single-patient-use KwikPen: four doses, dialled by the device in milligrams. No units.
Every branded dose, in units
This is the part that surprises people. Lilly keeps the injection volume constant and changes the concentration instead, which is why the unit count never moves across the six strengths.
| Dose | Single-dose vial | Units on U-100 | Multi-dose vial | Units on U-100 |
|---|---|---|---|---|
| 2.5 mg | 2.5 mg/0.5 mL (5 mg/mL) | 50 units | 10 mg/2.4 mL (4.17 mg/mL) | 60 units |
| 5 mg | 5 mg/0.5 mL (10 mg/mL) | 50 units | 20 mg/2.4 mL (8.33 mg/mL) | 60 units |
| 7.5 mg | 7.5 mg/0.5 mL (15 mg/mL) | 50 units | 30 mg/2.4 mL (12.5 mg/mL) | 60 units |
| 10 mg | 10 mg/0.5 mL (20 mg/mL) | 50 units | 40 mg/2.4 mL (16.7 mg/mL) | 60 units |
| 12.5 mg | 12.5 mg/0.5 mL (25 mg/mL) | 50 units | 50 mg/2.4 mL (20.8 mg/mL) | 60 units |
| 15 mg | 15 mg/0.5 mL (30 mg/mL) | 50 units | 60 mg/2.4 mL (25 mg/mL) | 60 units |
Two things fall out of that table. A unit count on its own carries no information about dose on branded tirzepatide, because 50 units is every dose. And 25 mg/mL appears twice in different roles: it is the 12.5 mg single-dose vial and the 15 mg multi-dose vial. The concentration alone does not identify the dose either.
The compounded concentrations, converted
Compounded tirzepatide is supplied in multi-dose vials at concentrations the pharmacy chooses, commonly between 5 mg/mL and 34 mg/mL. Each column below is a different vial. Figures are rounded to the nearest tenth of a unit.
| Dose | 5 mg/mL | 10 mg/mL | 15 mg/mL | 20 mg/mL | 30 mg/mL | 34 mg/mL |
|---|---|---|---|---|---|---|
| 2.5 mg | 50 units | 25 units | 16.7 units | 12.5 units | 8.3 units | 7.4 units |
| 5 mg | 100 units | 50 units | 33.3 units | 25 units | 16.7 units | 14.7 units |
| 7.5 mg | 150 units* | 75 units | 50 units | 37.5 units | 25 units | 22.1 units |
| 10 mg | 200 units* | 100 units | 66.7 units | 50 units | 33.3 units | 29.4 units |
| 12.5 mg | 250 units* | 125 units* | 83.3 units | 62.5 units | 41.7 units | 36.8 units |
| 15 mg | 300 units* | 150 units* | 100 units | 75 units | 50 units | 44.1 units |
*Marked cells exceed the 100-unit capacity of a standard U-100 syringe, so they cannot be drawn in one go. A figure above 100 units is usually a sign that the concentration assumed is wrong rather than that several injections are needed.
The same volumes expressed in millilitres, which is how most vial labels and prescriptions are written, are in our mg to mL conversion table. The starting dose gets asked about more than the rest combined, and it has its own page: how many units is 2.5 mg of tirzepatide.
The arithmetic, once
Units equals the dose in milligrams divided by the concentration in mg/mL, multiplied by 100. A 7.5 mg dose from a 15 mg/mL vial is 7.5 divided by 15, which is 0.5 mL, which is 50 units. Reversed: millilitres equals units divided by 100, and milligrams equals that volume multiplied by the concentration.
Where 50 units becomes a six-fold error
Because 50 units is the correct unit count for every branded single-dose vial, it circulates as though it were the unit count for tirzepatide generally. It is not. It is the unit count for a 0.5 mL fill, and a compounded vial is a different fill at a different strength.
Drawn from a 30 mg/mL compounded vial, 50 units is 0.5 mL, which is 15 mg. That is the maximum labelled dose arriving in place of the 2.5 mg starting dose, a six-fold error from copying a number rather than doing the division. FDA has reported adverse events, some requiring hospitalisation, from dosing errors with compounded GLP-1 products, with most reports describing patients drawing up more than the prescribed amount from a multiple-dose vial and administering five to 20 times the intended dose.
The published case reports point the same way. A poison centre series of three compounded semaglutide administration errors included two ten-fold overdoses, and one patient described dosing in millilitres and units rather than milligrams. A separate series of three semaglutide overdoses on initiation included a patient who injected 2 mg instead of 0.1 mg. In all six cases the result was days of gastrointestinal symptoms rather than hypoglycaemia, because the insulin-releasing effect of these drugs is glucose-dependent.
Check a dose conversion before you draw it
Our calculator converts between milligrams, millilitres and syringe units for a given vial concentration.
Which of these doses has results behind it
The unit table covers all six labelled doses, but they are not all treatment doses. SURMOUNT-1 randomised 2539 adults with obesity and no diabetes to tirzepatide 5 mg, 10 mg or 15 mg for 72 weeks, including a 20-week escalation, and recorded mean weight changes of -15.0%, -19.5% and -20.9% against -3.1% on placebo. The 2.5 mg, 7.5 mg and 12.5 mg steps exist to get people to those doses and have no standalone 72-week figure.
The escalation schedule itself, including how long the label describes staying at each step, is set out in the tirzepatide dosage chart. Which dose anyone uses, and whether it changes, is a decision for the prescriber who wrote it.
What to confirm on the label before any arithmetic
Every number above depends on three facts printed on the carton or vial, not on anything inferable from the dose:
- The total strength and total volume, written as something like 60 mg/2.4 mL. The concentration is the first number divided by the second.
- The syringe scale. U-100 means 100 units per mL. A U-40 syringe, still sold for veterinary insulin, marks 40 units per mL, so the same marking is 2.5 times the volume.
- The prescribed dose in milligrams, as written by the prescriber. A unit figure from a forum, a video or another vial is not a substitute, and a pharmacist can confirm the conversion for the specific vial in hand.
FAQ
How many units is a tirzepatide dose?
On a branded single-dose pen or single-dose vial it is 50 units, because every strength from 2.5 mg to 15 mg is supplied as that dose in 0.5 mL. On the branded multi-dose vial it is 60 units, because each of the four doses is 0.6 mL. On a compounded vial there is no fixed answer: the unit count depends entirely on the concentration printed on that vial.
Why is every branded tirzepatide strength the same number of units?
Because Lilly varies the concentration rather than the volume. The 2.5 mg single-dose vial is 5 mg/mL and the 15 mg single-dose vial is 30 mg/mL, but both hold 0.5 mL, so both read 50 units on a U-100 syringe. The volume is constant and the strength per millilitre is what changes.
How many units is 2.5 mg of tirzepatide?
It depends on concentration: 50 units at 5 mg/mL, 25 units at 10 mg/mL, about 17 units at 15 mg/mL, 12.5 units at 20 mg/mL and about 8 units at 30 mg/mL. The dose-specific breakdown is covered separately in our page on how many units 2.5 mg of tirzepatide is.
What is the biggest error in these conversions?
Carrying the number 50 across from a branded vial to a compounded one. On a branded single-dose vial 50 units is one dose at any strength. On a compounded 30 mg/mL vial, 50 units is 15 mg, which is the maximum labelled dose rather than the starting one. FDA has reported adverse events in which patients administered five to 20 times the intended dose of compounded GLP-1 products.
Does the KwikPen have a unit count?
No. The single-patient-use KwikPen holds four weekly doses at 4.17 to 25 mg/mL and is dialled in milligrams by the device, so no syringe and no unit conversion are involved. The same is true of the single-dose pens, which are fixed-dose autoinjectors.
Which tirzepatide doses have published weight-loss results?
SURMOUNT-1 measured 5 mg, 10 mg and 15 mg in 2539 adults with obesity and no diabetes over 72 weeks, recording mean changes of -15.0%, -19.5% and -20.9% respectively. The intermediate 2.5 mg, 7.5 mg and 12.5 mg steps were escalation doses in that trial and have no standalone 72-week result.
Sources
- MOUNJARO (tirzepatide) injection, US prescribing information, Eli Lilly and Company. Sections 3 and 16: single-dose pen and vial 2.5 to 15 mg per 0.5 mL; multi-dose vial and KwikPen four doses at 4.17 to 25 mg/mL.
- ZEPBOUND (tirzepatide) injection, US prescribing information, Eli Lilly and Company. Sections 3 and 16: identical presentations and strengths.
- Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). N Engl J Med. 2022;387(3):205-216. PMID: 35658024
- Lambson JE, Flegal SC, Johnson AR. Administration errors of compounded semaglutide reported to a poison control center: case series. J Am Pharm Assoc. 2023;63(5):1643-1645. PMID: 37392810
- Wiener BG, Gnirke M, Vassallo S, Smith SW, Su MK. Challenges with glucagon-like peptide-1 (GLP-1) agonist initiation: a case series of semaglutide overdose administration errors. Clin Toxicol (Phila). 2024;62(2):131-133. PMID: 38470137
- US Food and Drug Administration. FDA alerts health care providers, compounders and patients of dosing errors associated with compounded injectable semaglutide products. Compounding risk alert, July 2024.
This article is for information only and is not medical advice. Dosing, suitability and any change to treatment are decisions for your prescriber.