Compounded semaglutide is supplied in vials, not prefilled pens. Unlike brand-name Ozempic and Wegovy — which come at a fixed, standardized concentration — compounded vials vary. Different pharmacies formulate at different concentrations, and the same pharmacy may ship different concentrations across different order sizes or time periods.
This variability is not a problem as long as you understand what concentration means and how it affects the volume you draw. The milligram dose your prescriber sets stays fixed. The milliliter volume you draw from a specific vial changes with every concentration. Getting these two things confused is the most common source of dosing error with compounded GLP-1 medications.
Volume (mL) = Dose (mg) ÷ Concentration (mg/mL)
What Concentration Actually Means
Concentration is the amount of active medication dissolved in each milliliter of solution. A vial labeled 5 mg/mL contains 5 milligrams of semaglutide in every 1 milliliter of liquid. A vial labeled 2.5 mg/mL contains half as much per milliliter — so you need to draw twice the volume to get the same dose.
The total amount of medication in the vial depends on both concentration and vial size. A 2 mL vial at 5 mg/mL contains 10 mg total. The same 2 mL vial at 2.5 mg/mL contains 5 mg total. Concentration and total content are related but distinct.
The Four Most Common Concentrations
Lowest common concentration. Largest draw volumes. Often used for very low starting doses where small-volume precision is difficult.
High volumeA moderate concentration that covers the full standard titration range without requiring very small or very large draw volumes.
VersatileWidely used. Smaller draw volumes than 2.5 mg/mL. Good for mid-to-high doses. Starting doses (0.25 mg) require very precise small draws.
CommonHigh concentration. Very small draw volumes throughout the titration range. Requires careful syringe reading — small errors represent large dose percentages.
High precision neededHow Concentration Affects Draw Volume
The relationship is inverse and linear: double the concentration, halve the draw volume — for the same dose. This chart shows what a 1.0 mg dose requires at each concentration:
The dose is identical in every row. Only the volume changes. A patient switching from a 1 mg/mL vial to a 5 mg/mL vial must draw one-fifth the volume to receive the same dose — not the same volume as before.
Reference Tables by Concentration
All tables below assume a U-100 insulin syringe. To convert mL to U-100 units: multiply by 100.
| Dose | Volume (mL) | U-100 Units |
|---|---|---|
| 0.25 mg | 0.25 mL | 25 units |
| 0.5 mg | 0.50 mL | 50 units |
| 1.0 mg | 1.00 mL | 100 units |
| 1.7 mg | 1.70 mL* | 170 units* |
| 2.4 mg | 2.40 mL* | 240 units* |
* Exceeds 1 mL syringe capacity. Higher doses at 1 mg/mL may require a 3 mL syringe or a higher-concentration vial.
| Dose | Volume (mL) | U-100 Units |
|---|---|---|
| 0.25 mg | 0.10 mL | 10 units |
| 0.5 mg | 0.20 mL | 20 units |
| 1.0 mg | 0.40 mL | 40 units |
| 1.7 mg | 0.68 mL | 68 units |
| 2.4 mg | 0.96 mL | 96 units |
| Dose | Volume (mL) | U-100 Units |
|---|---|---|
| 0.25 mg | 0.05 mL | 5 units |
| 0.5 mg | 0.10 mL | 10 units |
| 1.0 mg | 0.20 mL | 20 units |
| 1.7 mg | 0.34 mL | 34 units |
| 2.4 mg | 0.48 mL | 48 units |
| Dose | Volume (mL) | U-100 Units |
|---|---|---|
| 0.25 mg | 0.025 mL | 2.5 units |
| 0.5 mg | 0.05 mL | 5 units |
| 1.0 mg | 0.10 mL | 10 units |
| 1.7 mg | 0.17 mL | 17 units |
| 2.4 mg | 0.24 mL | 24 units |
Note: At 10 mg/mL, a 0.25 mg starting dose requires drawing to 2.5 units — between tick marks on most syringes. A 0.3 mL precision syringe is strongly recommended at this concentration for low doses.
Need help calculating your dose?
Use the GLP-1 dosage calculator.
Choosing the Right Syringe for Your Concentration
Syringe recommendations by concentration and dose
| Concentration | Low Doses (≤0.5 mg) | Mid–High Doses (≥1.0 mg) |
|---|---|---|
| 1 mg/mL | 0.5 mL syringe | 1 mL or 3 mL syringe |
| 2.5 mg/mL | 0.3 mL syringe | 0.5 mL or 1 mL syringe |
| 5 mg/mL | 0.3 mL syringe | 0.5 mL syringe |
| 10 mg/mL | 0.3 mL precision syringe | 0.3–0.5 mL syringe |
The general rule: use the smallest syringe whose capacity comfortably fits your draw volume. Smaller syringes have finer tick graduations, which matters most when draw volumes are small.
Common Mistakes
Drawing the same volume when switching to a new concentration. This is the most consequential error. If your previous vial was 2.5 mg/mL and your new vial is 5 mg/mL, drawing the same volume as before delivers twice your intended dose. Always recalculate volume from scratch when you receive a new vial — even if your prescribed dose has not changed.
Not reading the vial label before every draw. Vial labels from the same pharmacy can differ between batches or shipments. A label that says 5 mg/mL this month may say 2.5 mg/mL next month. Read the label printed on your specific vial, not the one from a previous order.
Using a standard 1 mL syringe at low concentrations for high doses. A 1.7 mg dose at 1 mg/mL requires 1.70 mL — more than a standard 1 mL syringe holds. Attempting to draw more than a syringe's rated capacity is not possible and not safe. If your concentration and dose combination exceeds 1 mL, you need a larger syringe or a higher-concentration vial.
Underestimating precision demands at high concentrations. At 10 mg/mL, a single unit on a U-100 syringe represents 0.1 mg of semaglutide — not 0.01 mg as it would with a 1 mg/mL vial. A one-unit reading error at 10 mg/mL causes a 10× larger dose error than the same one-unit mistake at 1 mg/mL. Higher concentration demands higher reading accuracy.
Frequently Asked Questions
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