Semaglutide is a once-weekly injectable medication used to manage type 2 diabetes and support chronic weight management. It comes in pre-filled pens that deliver fixed doses measured in milligrams (mg), but many people who use insulin syringes for compounded versions need to convert those mg doses into insulin syringe units. The question “how many units is 0.25 mg?” arises most often when switching from branded pens (Ozempic or Wegovy) to a vial of compounded semaglutide.
The answer depends entirely on the concentration of the solution in the vial. Unlike insulin, which has a standard concentration (U-100 = 100 units per mL), compounded semaglutide has no universal standard. Different pharmacies prepare different strengths, so 0.25 mg can equal very different unit markings on a syringe.
This article explains how to perform the conversion safely, why concentration matters so much, the most common strengths used in compounding pharmacies, and the steps you should take before drawing any dose. The content is for informational purposes only and not medical advice. Semaglutide dosing errors can cause serious high or low blood sugar—never calculate or inject a dose without direct guidance from your prescribing physician or pharmacist.
Why Semaglutide Units Are Not Standardized Like Insulin
Insulin is almost always U-100 (100 units = 1 mL), so 10 units always equals 0.1 mL no matter which brand or vial you use. Semaglutide does not have a standardized “U” concentration. Branded Ozempic and Wegovy pens deliver fixed mg doses through a mechanical dial, so the user never needs to think in units or milliliters.
Compounded semaglutide, however, comes in multi-dose vials where the pharmacy decides the concentration (mg of semaglutide per mL of solution). The same 0.25 mg dose can require 0.05 mL from one vial and 0.10 mL from another depending on how the pharmacist mixed it. This variability is why you must know the exact concentration written on your vial label before drawing any dose.
Using the wrong conversion (for example, assuming every compounded vial is the same strength as another pharmacy’s vial) can lead to serious under-dosing or over-dosing.
The Two Most Common Compounded Concentrations
Most compounding pharmacies choose one of two practical strengths for semaglutide vials: 2.5 mg/mL or 5 mg/mL. These concentrations make the most common doses (0.25 mg, 0.5 mg, 1 mg, 1.7 mg, 2.4 mg) easy to draw with standard U-100 insulin syringes (1 mL = 100 units).
- 2.5 mg/mL concentration
0.25 mg = 0.1 mL = 10 units on a U-100 syringe
0.5 mg = 0.2 mL = 20 units
1 mg = 0.4 mL = 40 units
1.7 mg = 0.68 mL = 68 units
2.4 mg = 0.96 mL = 96 units - 5 mg/mL concentration
0.25 mg = 0.05 mL = 5 units on a U-100 syringe
0.5 mg = 0.1 mL = 10 units
1 mg = 0.2 mL = 20 units
1.7 mg = 0.34 mL = 34 units
2.4 mg = 0.48 mL = 48 units
Always check the label on your specific vial. Some pharmacies use 1 mg/mL, 3 mg/mL, or other strengths, which changes the unit calculation completely.
Step-by-Step: How to Calculate Units for Any Concentration
Follow these three steps every time you draw a dose from a compounded vial:
- Read the concentration on the vial label (example: “5 mg/mL” or “2.5 mg per 1 mL”).
- Divide the prescribed mg dose by the concentration to get the volume in mL.
Formula: Volume (mL) = Desired dose (mg) ÷ Concentration (mg/mL) - Multiply the mL by 100 to get insulin syringe units (because U-100 syringes have 100 units per mL).
Formula: Units = Volume (mL) × 100
Example calculations using a 5 mg/mL vial:
- 0.25 mg → 0.25 ÷ 5 = 0.05 mL → 0.05 × 100 = 5 units
- 0.5 mg → 0.5 ÷ 5 = 0.1 mL → 0.1 × 100 = 10 units
- 1 mg → 1 ÷ 5 = 0.2 mL → 0.2 × 100 = 20 units
Repeat the math for every dose increase until you reach maintenance.
Comparison of Common Vial Strengths & Resulting Unit Markings
| Vial Concentration | 0.25 mg Dose (units on U-100 syringe) | 0.5 mg Dose (units) | 1 mg Dose (units) | Notes |
|---|---|---|---|---|
| 2.5 mg/mL | 10 units | 20 units | 40 units | Larger volume per dose |
| 5 mg/mL | 5 units | 10 units | 20 units | Smaller volume, easier for low doses |
| 1 mg/mL | 25 units | 50 units | 100 units | Larger volume, less common |
This table shows why knowing the exact concentration on your vial is critical. The same mg dose can require very different syringe markings depending on strength.
How to Draw and Inject Accurately
Use only U-100 insulin syringes (orange cap, 1 mL = 100 units). Never use a tuberculin syringe or any other syringe type—the markings will be wrong. Wash your hands, wipe the vial stopper with an alcohol pad, and draw air into the syringe equal to your dose.
Inject the air into the vial, then turn the vial upside down and draw slightly more than your calculated units. Tap out air bubbles and push the plunger back to the exact unit mark. Pinch the skin, insert the needle at a 90-degree angle, and inject slowly. Hold for 5–10 seconds before withdrawing to reduce leakage.
Rotate injection sites (abdomen, thigh, upper arm) each week to prevent irritation or lumps. Dispose of used syringes in a sharps container.
Safe Injection Checklist
- Confirm concentration on vial label every time
- Use only U-100 insulin syringes
- Wipe vial stopper with alcohol before each draw
- Tap out air bubbles and double-check unit mark
- Rotate sites weekly
- Never reuse needles or syringes
These steps minimize dosing errors and injection-site reactions.
Storage and Handling to Maintain Potency
Keep unopened compounded semaglutide vials refrigerated at 36–46°F (2–8°C) until the beyond-use date on the label (usually 28–30 days after first puncture). After first use, most pharmacies instruct continuous refrigeration. Do not freeze—freezing destroys the active ingredient.
Branded Ozempic pens have more flexible rules: unopened pens stay refrigerated until expiration; opened pens can be kept at room temperature (≤86°F / 30°C) for up to 56 days. Compounded vials generally do not have this room-temperature allowance.
Protect vials from light (keep in the original box or a dark container) and avoid storing in the refrigerator door where temperatures fluctuate.
Storage Tips
- Refrigerate continuously (check pharmacy label)
- Keep in original box or opaque container to block light
- Never freeze—discard if frozen
- Do not use after the beyond-use date
- Keep away from heat sources and direct sunlight
Proper storage preserves potency throughout the vial’s life.
Common Mistakes That Affect Dosing Accuracy
The most frequent error is assuming all compounded semaglutide is the same strength. A patient who used a 5 mg/mL vial and then receives a 2.5 mg/mL vial without recalculating will draw twice the intended volume and double the dose.
Another common mistake is using the wrong syringe type. Tuberculin syringes (black markings, 1 mL = 100 units but different scale) or other insulin syringes (U-40, U-500) give incorrect readings on a U-100 syringe.
Shaking the vial vigorously can create air bubbles or degrade the solution. Gentle rolling between the palms is sufficient to mix if needed.
Mistakes to Avoid
- Assuming concentration is the same as a previous vial
- Using the wrong syringe type (must be U-100 insulin syringe)
- Shaking the vial instead of gentle rolling
- Not double-checking math before every draw
- Storing at room temperature when refrigeration is required
Double-checking the label and calculation every time prevents errors.
Conclusion
Semaglutide is not measured in “units” like insulin—the dose is always in milligrams (mg). To know how many units 0.25 mg represents on a U-100 insulin syringe, divide 0.25 by the concentration (mg/mL) on your vial label, then multiply the result by 100. The most common concentrations are 2.5 mg/mL (10 units) and 5 mg/mL (5 units), but pharmacies can use other strengths, so the label is the only reliable source. This article is for informational purposes only and not medical advice. Never draw or inject semaglutide without confirming the concentration and calculation with your prescribing provider or pharmacist—errors can cause serious high or low blood sugar. Keep the vial label visible and double-check every dose.
FAQ
How do I calculate units for 0.25 mg semaglutide?
Divide 0.25 mg by the concentration on your vial label (mg/mL), then multiply by 100. Example: 5 mg/mL vial → 0.25 ÷ 5 = 0.05 mL → 0.05 × 100 = 5 units on a U-100 syringe.
What syringe should I use for compounded semaglutide?
Use only U-100 insulin syringes (orange cap, 100 units = 1 mL). Tuberculin syringes or other types have different markings and will give the wrong dose. Never use a syringe without clear unit markings.
Why do different pharmacies have different unit numbers for the same dose?
Pharmacies choose different concentrations (2.5 mg/mL, 5 mg/mL, etc.). The same 0.25 mg dose requires 10 units from a 2.5 mg/mL vial but only 5 units from a 5 mg/mL vial. Always check the label on your vial.
What happens if I draw the wrong number of units?
Drawing too few units under-doses the medication and reduces effectiveness. Drawing too many units over-doses and can cause severe nausea, vomiting, low blood sugar, or other side effects. Contact your provider immediately if you suspect an incorrect dose.
How do I know the concentration of my compounded semaglutide?
The concentration (mg/mL) must be clearly printed on the vial label. If it is missing or unclear, do not use the vial—contact the compounding pharmacy immediately for clarification.
Can I use an insulin pen instead of drawing from a vial?
No. Compounded semaglutide comes in vials, not pre-filled pens. Branded Ozempic and Wegovy pens are the only pre-filled devices. Never attempt to transfer compounded solution into an empty pen.
How should I store compounded semaglutide?
Most pharmacies instruct continuous refrigeration at 36–46°F (2–8°C). Do not freeze. Protect from light by keeping the vial in its box or a dark container. Follow the exact storage and beyond-use date on your label.
What if my compounded vial looks cloudy or has particles?
Do not use it. Cloudiness, particles, discoloration, or unusual odor indicate possible contamination or degradation. Discard immediately and contact the pharmacy for a replacement.
Is it safe to switch from Ozempic pens to compounded semaglutide?
Switching is possible but requires medical supervision. Dosing must be recalculated based on the new concentration, and you should monitor blood sugar or weight closely during the transition. Your doctor will guide the change.
Who should I ask if I’m unsure about units or concentration?
Ask your prescribing physician or the compounding pharmacy pharmacist. They have the exact concentration used and can walk you through the calculation for every dose increase. Never guess or rely on online charts without verifying your vial.
Dr. Usman is a medical content reviewer with 12+ years of experience in healthcare research and patient education. He specializes in evidence-based health information, medications, and chronic health topics. His work is based on trusted medical sources and current clinical guidelines to ensure accuracy, transparency, and reliability. Content reviewed by Dr. Usman is for educational purposes and does not replace professional medical advice.