Free tool · Compounded GLP-1 dosing
Your dose is in milligrams. Your syringe counts in units.
Enter the dose your prescriber gave you and read the numbers off your vial. The tool shows how many units to draw, and how much of any additive comes along with it.
1. Your medication
The same drug that is in Zepbound, Mounjaro. Compounded versions are made by a pharmacy and are not FDA-approved.
2. Your dose, in milligrams
This is the number your prescriber said, like "2.5 mg." If you were only ever told a number of units, ask what that is in milligrams. Units on their own do not say how much medicine you are taking.
3. What your vial label says about the tirzepatide
Use the line for the tirzepatide only. If your vial has an additive, the label lists it on its own line with its own strength. Do not add the two numbers together.
4. Is anything else in the vial?
An additive does not change how many units you draw. It only rides along in the same liquid. Leave its strength blank if your label does not show one.
5. Your syringe
The biggest number on the barrel is its size. This tool assumes a U-100 insulin syringe, which is printed on the package and usually on the syringe. If yours says anything other than U-100, stop and call your pharmacy.
Draw this much
2.5 mg of tirzepatide = 0.25 mL of liquid = 25 units on a U-100 syringe
The math: 2.5 mg ÷ 10 mg per mL = 0.25 mL. A U-100 syringe holds 100 units in every mL, so 0.25 mL × 100 = 25 units.
Each injection also carries 0.125 mg of Vitamin B12. That comes from the same 0.25 mL, so it does not change the number of units.
A 30-unit syringe would also hold this dose, and smaller syringes have lines that are further apart and easier to read.
A slipped decimal point is the most common way this goes wrong. If you ever find yourself drawing 250 units for this dose, stop. That is ten times as much.
Every standard tirzepatide step, from this vial
At 10 mg per mL. Useful when your dose goes up and the vial stays the same. A new vial can be a different strength, so check the label every refill.
| Dose | mL | Units |
|---|---|---|
| 2.5 mg | 0.25 | 25 |
| 5 mg | 0.5 | 50 |
| 7.5 mg | 0.75 | 75 |
| 10 mg | 1 | 100 |
| 12.5 mg | 1.25 | 125 (more than 1 mL) |
| 15 mg | 1.5 | 150 (more than 1 mL) |
This is education, not medical advice
This tool does arithmetic on the numbers you type. It cannot see your vial, your syringe or your prescription. Before your first injection from any new vial, have your pharmacist or prescriber confirm the number of units, and ask for it in writing.
Why milligrams turn into units
Milligrams are the medicine
When a prescriber says your dose is 2.5 mg of tirzepatide, that is the amount of drug going into your body. It is the same number used on the brand-name labels and in the clinical trials, and it is the number that goes up as your dose steps up.
Units are the liquid
A compounded vial is the drug dissolved in liquid, and you cannot see milligrams in a syringe. What you can see is how much liquid you pulled up. The syringes pharmacies send with these vials are insulin syringes, and insulin syringes are marked in units. On a U-100 syringe, 100 units is exactly 1 mL, so every line is a hundredth of a milliliter. A "unit" here is only a measure of volume. It has nothing to do with the drug.
The label connects the two
The strength on the label, in milligrams per milliliter, is what turns one into the other. That is why the same 2.5 mg dose can be 25 units from a 10 mg/mL vial, 31 units from an 8 mg/mL vial and 12.5 units from a 20 mg/mL vial. Nothing about your dose changed. The liquid did. So a number of units only means something next to the vial it came from, and "I take 25 units" tells another person nothing unless they also know the strength.
Where the additive fits
Many compounded GLP-1s come mixed with something else, most often vitamin B12, and sometimes B6, glycine, L-carnitine or NAD+. Because each pharmacy makes its own blend, the strength of the GLP-1 varies from one pharmacy to the next, and even between products from the same pharmacy. That is the main reason compounded doses are given in units: there is no one standard vial to write the dose against. The additive itself shares the same liquid. Every unit you draw carries some of each, in the proportions on the label, so you work out your units from the GLP-1's strength and the additive's amount follows. No additive was part of the trials that approved these medications.
Why the brand vials are different
Zepbound also comes in vials, and Lilly solved the same problem the other way round. Each single-dose vial holds 0.5 mL at a different strength, so 2.5 mg and 15 mg are both 0.5 mL. With the brand vials the liquid stays the same and the strength changes. With a compounded vial the strength stays the same and the liquid changes, which is why you need a number of units that is yours alone.
What the FDA has seen go wrong
In 2024 the FDA warned about dosing errors with compounded semaglutide in multiple-dose vials. In the reports, patients drew five to 20 times the intended dose, often from mixing up milliliters, milligrams and units, or from being handed a syringe much larger than the dose. One patient told to take 5 units took 50. Prescribers made the same slip: one meant 0.25 mg, which was 5 units, and wrote 25 units. A poison control center reported the same pattern the year before. The people who were hurt had nausea, vomiting, dehydration, pancreatitis and gallstones, and some needed hospital care.
Before every new vial
- Read the tirzepatide strength on the label. A refill can be a different strength from the last vial.
- Check the syringe package says U-100, and use the smallest syringe your dose fits in.
- Ask for your dose in both milligrams and units, in writing.
- If the units you were given do not match what this tool shows, do not inject until your pharmacy or prescriber has explained the difference.
Sources
4 references
- US Food and Drug Administration. FDA alerts health care providers, compounders and patients of dosing errors associated with compounded injectable semaglutide products. July 2024. fda.gov. The five-to-20-times overdoses, the 5-unit (0.05 mL) dose drawn as 50 units, the prescriber conversion errors, the varying concentrations between compounders, and the advice to match the syringe size to the dose.
- Lambson JE, Flegal SC, Johnson AR. Administration errors of compounded semaglutide reported to a poison control center: case series. Journal of the American Pharmacists Association. 2023;63(5):1643–1645. doi:10.1016/j.japh.2023.06.017.
- Zepbound (tirzepatide) Prescribing Information, Dosage and Administration and Dosage Forms and Strengths. Eli Lilly and Company. Current label at DailyMed. The 2.5 to 15 mg dose steps and the 0.5 mL single-dose vial at every strength.
- Wegovy (semaglutide) Prescribing Information, Dosage and Administration. Novo Nordisk. Current label at DailyMed. The 0.25 to 2.4 mg dose steps and the 7.2 mg Wegovy HD dose.
Coaching
Would it help to talk this through with me?
A calculator can do the conversion. Coaching helps with the rest: the questions to ask your pharmacy, the dose steps ahead, and the weeks in between.
Work with me →