Vials & syringes
Units to mg: how to read your semaglutide or tirzepatide syringe
Medically reviewed by Linda West-Conforti, RN · CA RN #389453 ·
On a U-100 syringe, 100 units fill 1 mL, so each unit is 0.01 mL. To turn units into mg, divide the units by 100 and multiply by the concentration (mg/mL) printed on your vial label. On July 26, 2024 the FDA warned that mixing up units, mL and mg led to doses 5 to 20 times too high.
What is a “unit” on a semaglutide or tirzepatide syringe?
Quick answer: A unit is a volume mark on a U-100 syringe: 100 units fill 1 mL, so 1 unit is 0.01 mL. It measures liquid, not medicine.
Use the dose on your label from your REMEVi provider; this page explains the units, it does not set your dose. If anything on this page doesn’t match your label, stop and call before you inject.
REMEVi’s compounded semaglutide and tirzepatide come in multiple-dose vials, and you draw each dose with an insulin-type syringe marked “U-100.” The name comes from insulin: Lilly’s Humulin® R label describes its strength as “100 units/mL (U-100)” (label revised 06/2023). So on a U-100 syringe, the full 100 marks hold 1 mL of liquid, and every single mark holds one hundredth of a millilitre.
That is the key idea: a unit tells you how much liquid is in the syringe. It does not tell you how much semaglutide or tirzepatide is in that liquid. That depends on how strong the liquid is — its concentration, written in milligrams per millilitre (mg/mL) on the vial label. Two vials of different strength put different amounts of medicine behind the same unit mark.
| Unit mark on the syringe | Volume | Share of a 1 mL (100-unit) syringe |
|---|---|---|
| 5 units | 0.05 mL | 5% |
| 10 units | 0.1 mL | 10% |
| 15 units | 0.15 mL | 15% |
| 20 units | 0.2 mL | 20% |
| 25 units | 0.25 mL | 25% |
| 30 units | 0.3 mL | 30% |
| 40 units | 0.4 mL | 40% |
| 50 units | 0.5 mL | 50% |
Volume only. How much medicine that volume holds depends on the concentration printed on your vial.
How do you convert units to mg?
Quick answer: Divide the units by 100 to get mL, then multiply by the mg/mL on your vial label. The result is the mg in the syringe.
The math has two steps, and you need one number from your vial label to do it:
- Find the concentration. Look on your vial label for a number written as mg/mL. That is how many milligrams of medicine are in each millilitre. Use the number on YOUR vial, not one from a website, a friend or an older vial.
- Units to mL. Divide the units by 100. Ten units is 0.1 mL; fifty units is 0.5 mL.
- mL to mg. Multiply the mL by the concentration. The answer is how many mg of medicine are in the syringe.
The same formula works backwards: units = mg ÷ concentration × 100. Your label should already tell you how many units to draw. If you run the math and it does not match your label, do not change anything on your own — call your REMEVi provider or the pharmacy first. The FDA reported that some errors came from the math itself, not only from reading the syringe.
How many mg is 10, 20 or 50 units of compounded semaglutide?
Quick answer: It depends on the vial. At 2.5 mg/mL, 20 units is 0.5 mg; at 5 mg/mL, 20 units is 1 mg. Use your label’s concentration.
The FDA notes that compounded semaglutide comes in varying concentrations, and that instructions may be written in “units,” whose volume of medicine “may vary depending on the concentration” (FDA, July 26, 2024). The table below shows the arithmetic at two example concentrations, 2.5 and 5 mg/mL. Look at any row: the unit mark and the mL stay put, while the mg change with the vial.
| Units | mL | mg if the vial is 2.5 mg/mL | mg if the vial is 5 mg/mL |
|---|---|---|---|
| 5 | 0.05 | 0.125 mg | 0.25 mg |
| 10 | 0.1 | 0.25 mg | 0.5 mg |
| 15 | 0.15 | 0.375 mg | 0.75 mg |
| 20 | 0.2 | 0.5 mg | 1 mg |
| 25 | 0.25 | 0.625 mg | 1.25 mg |
| 30 | 0.3 | 0.75 mg | 1.5 mg |
| 40 | 0.4 | 1 mg | 2 mg |
| 50 | 0.5 | 1.25 mg | 2.5 mg |
Arithmetic, not a dose. The concentrations are examples; the one printed on YOUR vial label is the number to use. If your label gives a different concentration, these mg figures do not apply to you.
How many mg is 10, 20 or 50 units of compounded tirzepatide?
Quick answer: Again, it depends on the vial. At 10 mg/mL, 20 units is 2 mg; at 17 mg/mL, it is 3.4 mg.
Compounded tirzepatide works the same way. The FDA’s page on unapproved GLP-1 drugs (current as of October 1, 2026) asks providers to be vigilant when prescribing compounded semaglutide or tirzepatide, and “encourages patients to talk with their health care provider or compounder about how to measure and administer the intended dose.” The table uses 10 and 17 mg/mL as examples.
| Units | mL | mg if the vial is 10 mg/mL | mg if the vial is 17 mg/mL |
|---|---|---|---|
| 5 | 0.05 | 0.5 mg | 0.85 mg |
| 10 | 0.1 | 1 mg | 1.7 mg |
| 15 | 0.15 | 1.5 mg | 2.55 mg |
| 20 | 0.2 | 2 mg | 3.4 mg |
| 25 | 0.25 | 2.5 mg | 4.25 mg |
| 30 | 0.3 | 3 mg | 5.1 mg |
| 40 | 0.4 | 4 mg | 6.8 mg |
| 50 | 0.5 | 5 mg | 8.5 mg |
Arithmetic, not a dose. The concentrations are examples; the one printed on YOUR vial label is the number to use. If your label gives a different concentration, these mg figures do not apply to you.
If a refill comes at a different concentration than your last vial, the number of units for the same amount of medicine changes. Before you inject from a vial whose label looks different, call your REMEVi provider and confirm how many units to draw.
Why did the FDA warn about dosing errors with compounded semaglutide?
Quick answer: Patients and prescribers mixed up units, mL and mg. Most reports involved drawing 5 to 20 times the intended dose from a multiple-dose vial.
In its alert of July 26, 2024, the FDA said it had received reports of adverse events, “some requiring hospitalization,” that may be related to overdoses from dosing errors with compounded injectable semaglutide. It named the cause plainly: “Unfamiliarity with withdrawing medication from a vial into a syringe and coupled with confusion between different units of measurement (e.g., milliliters, milligrams and ‘units’) may have contributed to dosing errors.”
Most reports described patients drawing more than the prescribed dose from a multiple-dose vial — five to 20 times the intended dose. In several, patients told to inject 5 units (0.05 mL) on a 1 mL U-100 syringe injected 50 units instead. Other reports involved prescribers: one meant to prescribe 5 units but wrote 25, and the patient received five times the intended dose and had severe vomiting.
The overdose effects the FDA listed include nausea, vomiting, abdominal pain, fainting, headache, migraine, dehydration, acute pancreatitis and gallstones. The FDA also asks prescribers and compounders to give patients a syringe sized for the dose and to teach them how to measure it.
How do I check my syringe against my label?
Quick answer: Match three things before every dose: the concentration on the vial, the units on your label and the scale on your syringe. If one doesn’t match, call first.
A short check catches the errors the FDA described:
- The vial. Read the mg/mL on the label. If it differs from your last vial, call before you inject.
- The instruction. Find the number of units on your prescription label. Units, mL and mg are three different numbers; make sure you are reading units.
- The syringe. Check it says U-100 and read the scale on the barrel to see what each line is worth. Some 0.3 mL syringes have a half-unit scale (embecta). More on sizes in which needle and syringe are used.
- The total. Before you inject, look at the plunger line again and compare it with the units on your label.
Questions about your vial, syringe or label? Message your REMEVi care team or call (702) 352-4746 before you inject.
Compounded semaglutide and tirzepatide are prepared by licensed pharmacies for an individual prescription. They are not FDA-approved, and the FDA has not reviewed them for safety, effectiveness or quality.
Frequently asked questions
Is 1 unit always 0.01 mL?
On a U-100 syringe, yes: 100 units fill 1 mL. But the mg of medicine in 1 unit depends on the concentration of the vial.
Where do I find my vial’s concentration?
On the vial label, written as mg/mL. If you can’t find it, call the pharmacy or REMEVi at (702) 352-4746 before you inject.
Can I use a different syringe from the one I was sent?
Ask first. The FDA asks prescribers and compounders to give patients a syringe sized for the intended dose, and some reported overdoses involved syringes much larger than the dose.
What should I do if I think I injected too much?
Call your REMEVi provider right away at (702) 352-4746. If symptoms are severe, call 911. The FDA lists nausea, vomiting, abdominal pain, fainting and dehydration among reported overdose effects.
Is compounded semaglutide FDA-approved?
No. Compounded semaglutide and tirzepatide are not FDA-approved. They are prepared by licensed pharmacies for an individual prescription.
See whether REMEVi fits you
Compounded semaglutide: From $159 per 4 weeks on the 24-week plan · or $199 every 4 weeks, cancel any time.
Compounded tirzepatide: From $225 per 4 weeks on the 24-week plan · or $269 every 4 weeks, cancel any time.
Each plan has one price, the same at every dose and every renewal, with no membership fee. Compounded medication is not FDA-approved.
Use the dose on your label from your REMEVi provider; this page explains the units, it does not set your dose.
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