How-to guide
Switching GLP-1 pharmacies: how to recalculate your units
People change compounding pharmacies for cost, availability or a new provider. A new pharmacy often uses a different concentration, which changes how many units your dose takes, even when the mg dose stays the same.
You drew 30 units from a 5 mg/mL vial, which is 1.5 mg. Your new vial is 10 mg/mL. Drawing 30 units from the new vial is 3 mg, twice the dose. Recalculate before your first dose from any new vial.
Keep the mg, recalculate the units
Your prescription is in milligrams. The number of units is only how that dose is measured with a syringe, for one particular concentration. When the concentration changes, the units change. Whether your mg dose stays the same is your prescriber's decision, not the pharmacy's.
Step by step
- Confirm your prescribed dose in mg. Check your prescription or ask your prescriber. If you only know a unit count and the old concentration, you can work back to mg: (units ÷ 100) × old concentration. For example, 30 units of 5 mg/mL is 1.5 mg.
- Read the new vial's concentration. Find the mg/mL on the new label. If it shows total amount and volume, such as "10 mg/2 mL", divide: 10 ÷ 2 = 5 mg/mL. If it is written per half mL, such as "5 mg/0.5 mL", double it: 10 mg/mL. If you cannot find it, call the pharmacy before you draw. More formats are shown below.
- Calculate the units. Use the formula below or the DoseCompa calculator.
- Check your syringe. Make sure the amount fits your syringe and lands on one of its printed lines.
- Ask if anything is unclear. If the label is confusing, the change is large, or the result falls between lines, ask your pharmacist or prescriber before your first dose from the new vial.
Examples
| Situation | Old vial | New vial | Calculated units |
|---|---|---|---|
| Semaglutide 1 mg | 20 units at 5 mg/mL | 10 mg/mL | 10 |
| Same switch, not recalculated | 20 units at 5 mg/mL | 10 mg/mL | 20 units would be 2 mg (twice the dose) |
| Tirzepatide 5 mg | 50 units at 10 mg/mL | 5 mg/mL | 100 (fills a whole 100-unit syringe) |
| Tirzepatide 5 mg | 62.5 units at 8 mg/mL | 16.6 mg/mL | about 30.1 (between printed lines) |
Examples only, assuming your prescriber keeps the same mg dose. Results between printed lines need guidance from your pharmacist or prescriber on how to measure them.
Your new label may be written differently
Pharmacies do not all write labels the same way. Your old vial may have said "10 mg/mL" while your new one says "5 mg/0.5 mL" or lists a second ingredient. Before your first dose, find the one number you need: how many mg of your GLP-1 medication are in each mL.
| If your new label says | What it means | Concentration to use |
|---|---|---|
| Tirzepatide 8 mg/0.5 mL | 8 mg in every half mL | 16 mg/mL |
| Semaglutide 10 mg/4 mL | 10 mg total in 4 mL | 2.5 mg/mL |
| Tirzepatide 60 mg/4 mL (15 mg/mL) | Total amount, with the per-mL strength in brackets | 15 mg/mL |
| Tirzepatide/Niacinamide 12 mg/2 mg/mL | Two ingredients. The numbers follow the names in order | 12 mg/mL (the first number) |
| Pyridoxine/Semaglutide 10 mg/2.5 mg/mL | The GLP-1 is named second, so it is the second number | 2.5 mg/mL |
| Tirzepatide/Glycine 12-4 mg/mL | The dash separates two ingredients. It is not a range | 12 mg/mL |
| Tirzepatide 20 mg, 2 mL vial | Unclear: 20 mg in total, or 20 mg in each mL? | Call the pharmacy before you draw |
Made-up examples to show the formats. Always use your own label. In DoseCompa, choose "mg per 0.5 mL" when your label is written per half mL.
Vials with B12, niacinamide, glycine or pyridoxine are common. Only the GLP-1 number is used to calculate your units. If you cannot tell which number belongs to your GLP-1 medication, ask the pharmacy.
If the result is not a clean number
A new concentration can give a unit count that is not a whole number, or that falls between the printed lines of your syringe. When the difference is tiny, DoseCompa shows the nearest printed line and the exact amount beside it. When a result is halfway between two lines, or the dose is small enough that rounding matters, ask your pharmacist or prescriber how to measure it, or whether a different syringe would fit your dose better. If the amount is more than your syringe holds, ask before you draw rather than splitting it yourself.
Moving from a pen to a vial
Brand-name pens are dosed with the pen itself, not with units on an insulin syringe. If you move from a pen to a compounded vial, your prescriber decides the compounded dose. Once you know that dose in mg and the vial's concentration, the unit math is the same as above.
Monthly vials with different concentrations
Some pharmacies send a new vial each month at a different concentration. Your unit count may stay the same or change, depending on both the dose and the concentration. Recalculate with every new vial instead of assuming.
Check your numbers. Enter your vial concentration, your prescribed dose and your syringe, and DoseCompa shows the calculated units and where they fall on your syringe's printed lines.
Open the calculatorQuestions
Do I have to restart my titration when I switch pharmacies?
That is a question for your prescriber. Changing pharmacies changes the concentration you measure from, so recalculate your units for the new vial, but your prescriber decides your dose and schedule.
How do I find my new pharmacy's concentration?
It should be on the vial label as mg/mL, or as a total amount and volume you can divide. If it is not clear, call the pharmacy.
My new vial is much more concentrated. Is that a problem?
A more concentrated vial means a smaller volume for the same mg dose, so a small measuring error matters more. Recalculate carefully, check that the amount lands on a printed line of your syringe, and ask your pharmacist if you are unsure.
What if I think I took the wrong amount?
Contact your prescriber or pharmacist. If you think you took too much or feel unwell, call Poison Control at 1-800-222-1222, and call 911 in an emergency.
My new vial has B12 or another added ingredient. Does that change my units?
No. Use only the GLP-1 concentration from the label to calculate your units. The added ingredient does not change the math. If the label does not make clear which number is the GLP-1, ask the pharmacy.
Should I round my units up or down?
For a tiny difference, like 41.67 units, the nearest printed line (42) is what DoseCompa shows, with the exact amount beside it. If a result is halfway between two lines, or your dose is small, ask your pharmacist how to measure it.
Can I combine two vials?
No. Never mix the contents of different vials. Ask your pharmacist what to do with any medication left in your old vial.