Can someone please explain the relationship between insulin syringe "units" and milligrams? I keep seeing people say "draw up 20 units" but my vial is labeled in mg. These are completely different measurement systems and it's driving me insane. I'm an engineer and even I find this needlessly confusing.
You're right to be frustrated — it IS confusing, and it's because we're repurposing insulin syringes for a non-insulin medication.
The key insight: "units" on an insulin syringe are volume markings, not drug units.
A U-100 insulin syringe (the standard type) is designed so that 100 "units" = 1 mL. That's it. The "units" on the syringe are just a volume measurement in disguise:
This is purely a volume-to-volume conversion. It has absolutely nothing to do with "units" of semaglutide, insulin units, international units, or any pharmacological unit of measure.
To convert syringe units to mg of semaglutide, you need to know your concentration (mg/mL).
Formula: mg = (syringe units ÷ 100) × concentration in mg/mL
Or equivalently: syringe units = (desired mg ÷ concentration in mg/mL) × 100
Building on the pharmacist's explanation above, here's a complete reference table for the most common compounded semaglutide concentrations. Bookmark this.
At 2mg/mL concentration:
| Dose (mg) | Volume (mL) | Syringe Units |
|---|---|---|
| 0.125 | 0.0625 | 6.25 units |
| 0.25 | 0.125 | 12.5 units |
| 0.50 | 0.25 | 25 units |
| 1.00 | 0.50 | 50 units |
| 1.70 | 0.85 | 85 units |
| 2.40 | 1.20 | Not possible with 1mL syringe! |
At 2.5mg/mL concentration:
| Dose (mg) | Volume (mL) | Syringe Units |
|---|---|---|
| 0.25 | 0.10 | 10 units |
| 0.50 | 0.20 | 20 units |
| 1.00 | 0.40 | 40 units |
| 1.70 | 0.68 | 68 units |
| 2.40 | 0.96 | 96 units |
At 5mg/mL concentration:
| Dose (mg) | Volume (mL) | Syringe Units |
|---|---|---|
| 0.25 | 0.05 | 5 units |
| 0.50 | 0.10 | 10 units |
| 1.00 | 0.20 | 20 units |
| 1.70 | 0.34 | 34 units |
| 2.40 | 0.48 | 48 units |
Notice how the 5mg/mL concentration makes everything much more compact, but the small volumes require precision. Use a 0.3mL or 0.5mL syringe with fine markings if you're working at this concentration.
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THANK YOU. This is the thing nobody says clearly. Every YouTube video I watched was like "just draw up to 20 units" without ever explaining that "units" here just means hundredths of a milliliter. Why on earth did they label them "units" instead of just putting mL markings on them?
Historical reasons. Insulin syringes were designed for U-100 insulin, where 100 "International Units" of insulin happen to be contained in 1 mL. So for insulin, the syringe markings directly correspond to units of the drug. It's only confusing when you use these syringes for a completely different medication — which is exactly what we're doing with compounded semaglutide.
The FDA-approved Ozempic pen avoids this entire problem because the pen dial is labeled directly in mg. But with compounded vials and insulin syringes, you're stuck doing the conversion yourself.