> Quick Answer: Medication concentration (mg/mL) tells you how much active ingredient is in each milliliter of liquid. Higher concentrations mean you inject less liquid for the same dose. Insulin syringes measure in "units" where 100 units = 1 mL. To calculate units needed: divide your dose (mg) by the concentration (mg/mL), then multiply by 100.
Why Understanding Dosing Matters
When using compounded GLP-1 medications, understanding how to accurately measure your dose is essential for:
- Safety: Avoiding under- or over-dosing
- Effectiveness: Ensuring you receive the prescribed therapeutic dose
- Confidence: Feeling comfortable with self-injection
This guide will explain everything you need to know about concentrations, units, and syringes.
Understanding Medication Concentration
What Does mg/mL Mean?
Concentration is expressed as milligrams per milliliter (mg/mL). This tells you how much active medication is dissolved in each milliliter of liquid.
Example:
- A 10mg/mL vial contains 10 milligrams of medication in every 1 mL of liquid
- A 20mg/mL vial contains 20 milligrams of medication in every 1 mL of liquid
The higher the concentration, the more potent each drop of liquid is.
Why Concentrations Vary
Compounded medications may come in different concentrations based on:
- Prescribed dose requirements
- Vial size and total medication amount
- Pharmacy formulation standards
- Cost and convenience factors
Important: Always verify your vial's concentration before drawing your dose. It's printed on the vial label.
Understanding Insulin Syringes
Why Insulin Syringes?
GLP-1 medications use insulin syringes because:
- They're designed for precise, small-volume subcutaneous injections
- The fine needles (typically 29-31 gauge) minimize discomfort
- They're widely available and standardized
How Syringe Units Work
Insulin syringes are marked in "units" rather than milliliters. Here's the key relationship:
100 units = 1 milliliter (mL)
This means:
- 50 units = 0.5 mL
- 25 units = 0.25 mL
- 10 units = 0.1 mL
Common Syringe Sizes
| Syringe Size | Maximum Volume | Best For |
| 0.3 mL (30 units) | 30 units | Low doses, high concentrations |
| 0.5 mL (50 units) | 50 units | Medium doses |
| 1.0 mL (100 units) | 100 units | Higher doses, lower concentrations |
Tip: Using a syringe size close to your dose volume makes measuring more accurate. If your dose is 25 units, a 0.3 mL or 0.5 mL syringe is easier to read than a 1.0 mL syringe.
The Dosing Formula
To calculate how many units to draw, use this formula:
Units = (Dose in mg ÷ Concentration in mg/mL) × 100
Example Calculation
You're prescribed 5 mg of tirzepatide and have a 20 mg/mL vial:
You would draw 25 units on your insulin syringe.
Tirzepatide Dosing Tables
Tirzepatide 20 mg/mL Concentration
| Prescribed Dose | Units to Draw | Volume (mL) |
| 2.5 mg | 12.5 units | 0.125 mL |
| 5 mg | 25 units | 0.25 mL |
| 7.5 mg | 37.5 units | 0.375 mL |
| 10 mg | 50 units | 0.5 mL |
| 12.5 mg | 62.5 units | 0.625 mL |
| 15 mg | 75 units | 0.75 mL |
Tirzepatide 10 mg/mL Concentration
| Prescribed Dose | Units to Draw | Volume (mL) |
| 2.5 mg | 25 units | 0.25 mL |
| 5 mg | 50 units | 0.5 mL |
| 7.5 mg | 75 units | 0.75 mL |
| 10 mg | 100 units | 1.0 mL |
| 12.5 mg | 125 units | 1.25 mL |
| 15 mg | 150 units | 1.5 mL |
Key Insight: Notice that the 20 mg/mL concentration requires exactly half the units compared to the 10 mg/mL concentration for the same dose.
Semaglutide Dosing Tables
Semaglutide 5 mg/mL Concentration
| Prescribed Dose | Units to Draw | Volume (mL) |
| 0.25 mg | 5 units | 0.05 mL |
| 0.5 mg | 10 units | 0.1 mL |
| 1 mg | 20 units | 0.2 mL |
| 1.7 mg | 34 units | 0.34 mL |
| 2.4 mg | 48 units | 0.48 mL |
Semaglutide 2.5 mg/mL Concentration
| Prescribed Dose | Units to Draw | Volume (mL) |
| 0.25 mg | 10 units | 0.1 mL |
| 0.5 mg | 20 units | 0.2 mL |
| 1 mg | 40 units | 0.4 mL |
| 1.7 mg | 68 units | 0.68 mL |
| 2.4 mg | 96 units | 0.96 mL |
Switching Between Concentrations
If your pharmacy provides a different concentration than your previous vial, you'll need to adjust the units you draw.
The Golden Rule
When concentration doubles, units are halved (for the same mg dose).
Example: Switching Tirzepatide Concentrations
You've been taking 5 mg from a 10 mg/mL vial (50 units). You receive a new 20 mg/mL vial.
- Old vial (10 mg/mL): 5 mg = 50 units
- New vial (20 mg/mL): 5 mg = 25 units
Your dose in milligrams stays the same. Only the units change.
Step-by-Step Injection Guide
1. Gather Your Supplies
- Medication vial
- Insulin syringe (appropriate size)
- Alcohol swabs
- Sharps container
2. Prepare the Vial
- Check the vial label for concentration and expiration date
- If refrigerated, let it warm to room temperature (reduces discomfort)
- Clean the rubber stopper with an alcohol swab
3. Draw the Medication
4. Prepare the Injection Site
- Choose a site: abdomen (2 inches from navel), front of thigh, or back of upper arm
- Rotate injection sites to prevent lipohypertrophy (tissue buildup)
- Clean the area with an alcohol swab and let dry
5. Inject the Medication
6. Dispose Safely
- Place the used syringe in a sharps container immediately
- Never recap needles
- Never reuse syringes
Common Dosing Mistakes to Avoid
Mistake #1: Confusing Units with Milligrams
Wrong thinking: "My dose is 5 mg, so I'll draw 5 units."
Correct approach: Always convert mg to units using the concentration. 5 mg from a 20 mg/mL vial = 25 units.
Mistake #2: Using the Wrong Concentration
Problem: Drawing the same number of units from a different concentration vial.
Prevention: Always check your vial concentration and recalculate units when you receive a new vial.
Mistake #3: Not Accounting for Air Bubbles
Problem: Air bubbles in the syringe reduce the actual medication volume.
Solution: Tap bubbles to the top and push them out before injecting. Small bubbles (less than a few units) aren't dangerous but do reduce your dose.
Mistake #4: Measuring from the Wrong Line
Problem: Reading from the top of the plunger rubber instead of the correct edge.
Solution: Read the measurement from the top edge of the black rubber plunger where it meets the barrel.
Frequently Asked Questions
What if I draw too much medication?
If you notice before injecting, simply push the excess back into the vial. If you've already injected, monitor for side effects (especially nausea) and contact your provider. Do not skip your next dose unless advised.
What if I draw too little medication?
You may experience reduced effectiveness. It's generally fine to draw an additional small amount to reach your prescribed dose, but avoid doing this habitually. Double-check your calculations.
Can I use the same syringe multiple times?
No. Reusing syringes increases infection risk and causes the needle to dull, making injections more painful and potentially causing tissue damage.
How do I handle half-unit doses (like 12.5 units)?
Some syringes have half-unit markings. If yours doesn't, aim for the midpoint between two unit lines. For very precise dosing, ask your pharmacy about half-unit syringes.
What if my vial has a different concentration than my previous one?
Recalculate your units using the formula above. Your milligram dose stays the same—only the units change. When in doubt, contact your pharmacy or provider.
Visual Guide: Reading Your Syringe
On an insulin syringe:
- The numbers represent units (not mg)
- 100 units = 1 mL
- Lines between numbers typically represent 1 or 2 units each (check your syringe)
- Read from the top edge of the black plunger
Pro tip: Hold the syringe at eye level when measuring for accuracy.
Quick Reference Card
Save this for easy reference:
To calculate units:
Units = (Dose mg ÷ Concentration mg/mL) × 100
Common conversions:
- 100 units = 1 mL
- 50 units = 0.5 mL
- 25 units = 0.25 mL
Before each injection:
When to Contact Your Provider
Reach out if you:
- Are unsure about your prescribed dose
- Receive a vial with a different concentration
- Experience unusual side effects
- Have difficulty with injection technique
- Have questions about dose adjustments
The Bottom Line
Understanding medication concentration and syringe units ensures you receive the correct dose every time. The key points to remember:
Taking the time to understand your dosing gives you confidence in your treatment and helps ensure optimal results.
Use our dosage calculator tool | Contact our care team
This guide is for educational purposes only. Always follow your healthcare provider's specific instructions for your medication. If you have any questions about your dose, contact your provider or pharmacist. Compounded medications are not FDA-approved finished drug products.