Semaglutide Reconstitution Calculator

Mixing Semaglutide: What to Know Before You Reconstitute

1. 01

   Why the arithmetic carries more weight here

   FDA has received multiple adverse event reports, some requiring hospitalization, that may relate to dosing errors with compounded injectable semaglutide. The agency attributes those errors to patients measuring and self-administering incorrect amounts, and in some cases to health care professionals miscalculating the amount. As of 31 May 2026 FDA had received 990 adverse event reports associated with compounded semaglutide. The conversion from milligrams in a vial to units on a syringe is the step where that error happens, which is the step this calculator does.

2. 02

   Check what is in the vial before you add anything

   A lyophilized vial holds a dry cake or a thin film of powder and needs liquid. A vial of solution is already liquid and is labeled with a strength per millilitre. If yours is solution, skip reconstitution entirely: read the printed mg/mL, enter it as your concentration, and the only conversion left is millilitres to syringe units.

   For reference, these are the concentrations FDA has approved on the current labels:

   Product	Presentation	Strength per mL
   Ozempic	Single-patient-use pen, 2 mg/3 mL	0.68 mg/mL
   Ozempic	Single-patient-use pen, 4 mg/3 mL	1.34 mg/mL
   Ozempic	Single-patient-use pen, 8 mg/3 mL	2.68 mg/mL
   Wegovy	Single-dose pen	Delivers one fixed amount, not measured by the user

3. 03

   Bacteriostatic water vs. sterile water

   Bacteriostatic water is sterile water containing 0.9% benzyl alcohol, a preservative that inhibits bacterial growth in the vial after it has been punctured. Sterile water has no preservative and is generally treated as single use. A compounded semaglutide vial is drawn from weekly over about a month, so bacteriostatic water is the standard choice.

4. 04

   How much water to add

   Water volume does not change how much semaglutide is in the vial. A 5 mg vial holds 5 mg whether you add 1 mL or 2 mL. What changes is concentration, and with it the size of every draw you take afterwards.

   Vial	Water	Concentration	Per syringe unit
   3 mg	1 mL	3.0 mg/mL	30 mcg
   5 mg	1 mL	5.0 mg/mL	50 mcg
   5 mg	2 mL	2.5 mg/mL	25 mcg
   10 mg	2 mL	5.0 mg/mL	50 mcg
   10 mg	4 mL	2.5 mg/mL	25 mcg

   The right-hand column is the one to read. It tells you how much peptide sits in a single unit on a U-100 syringe, so you can see immediately whether the amount on your prescription lands on a mark you can read or somewhere between two of them. Enter that amount in the calculator above and it returns the exact unit count.

5. 05

   Mixing technique

   Angle the needle so the water runs down the inside wall of the vial rather than landing on the powder, then let it sit or swirl gently until dissolved. Do not shake; it foams the solution. The result should be clear with no visible particles.

6. 06

   Storage, and the 28 day rule

   FDA's guidance on multi-dose compounded vials is specific and stricter than some compounder labels. The agency recommends discarding the vial within 28 days after first use even if medication remains in it, and not continuing to use it after 28 days even if the compounder's instructions say a longer period is fine. It also recommends a new sterile needle and syringe for every dose. Injectable GLP-1 drugs require refrigeration as stated in their package inserts, and FDA recommends not using one that arrives warm or with insufficient refrigeration. Weekly dosing makes the date matter more than the fill level: a vial can still hold solution when day 28 arrives.

7. 07

   The syringe

   U-100 insulin syringes are standard, where 100 units equal 1 mL and each unit is 0.01 mL. At 2.5 mg/mL a small amount lands on a low unit count, which is where the 0.3 mL 30-unit syringe earns its place: the same draw is spread across markings that are further apart and easier to read.

8. 08

   What FDA says about salt forms

   Some compounded products are semaglutide salts, such as semaglutide sodium and semaglutide acetate. FDA states these are different active ingredients from the one in the approved drugs, that it does not have information on whether they share the same chemical and pharmacologic properties, and that it is not aware of any lawful basis for their use in compounding. A salt form is not interchangeable with the base in your arithmetic, and the calculator cannot detect which one is in the vial.

9. 09

   Common mistakes worth avoiding

   The recurring ones: reconstituting a product that was already solution, mixing mg and mcg during the conversion, carrying a unit count over from a vial mixed at a different water volume, treating the printed strength of an approved pen as the concentration of a compounded vial, and reading past day 28 on the vial because solution is still left in it.