Semaglutide Reconstitution and Dosing: Syringe Units for Every Vial

Branded semaglutide injections come as a liquid with the dose already set. Wegovy single-dose pens and syringes hold 0.25, 0.5, or 1 mg in 0.5 mL, or 1.7 or 2.4 mg in 0.75 mL, and the Wegovy HD pen holds 7.2 mg in 0.75 mL. The Wegovy FlexTouch pen holds 9.6 mg in 3 mL and gives four 2.4 mg doses. Ozempic pens hold 2, 4, or 8 mg in 3 mL and dial up several weekly doses. None of these needs water or a syringe count.

A vial of freeze-dried powder needs bacteriostatic water added before use, and the number of units for each dose depends on the vial size and the volume you add. Compounded and research semaglutide is often sold this way, at 2, 5, or 10 mg a vial. The FDA declared the semaglutide shortage resolved on February 21, 2025, which narrowed when pharmacies may compound it, so check where a vial came from before you rely on its label.

Some compounded semaglutide arrives as a liquid with the strength on the label, for example 5 mg in 2 mL. The calculator handles these too: enter the total mg as the vial size and the total mL as the water volume.

The Wegovy prescribing information starts at 0.25 mg once weekly for 4 weeks, then steps to 0.5, 1, and 1.7 mg, four weeks each, before the maintenance dose of 2.4 mg (or 1.7 mg) from week 17. For weight reduction in adults who tolerate 2.4 mg for at least 4 weeks, the label now allows an increase to a maximum of 7.2 mg. The Ozempic prescribing information uses the same first two steps, then allows 1 mg and then 2 mg, each after at least 4 weeks on the dose before. Its maximum is 2 mg.

The weeks shown are the fastest pace each label allows. Wegovy's label suggests waiting another 4 weeks if a step is not tolerated, and Ozempic's maintenance dose can be 0.5, 1, or 2 mg. The 7.2 mg dose is supplied only as a single-dose pen (Wegovy HD), so the tables below stop at 2.4 mg. Which dose you take is your prescriber's decision.

Divide the vial's milligrams by the millilitres of water to get the concentration. Divide your dose by that concentration to get millilitres, then multiply by 100 to get units on a U-100 insulin syringe. As one formula:

A 5 mg vial mixed with 2 mL is 2.5 mg/mL. A 0.25 mg dose is 0.1 mL, which is 10 units. The reconstitution math blog works through each step with practice problems.

Values are units on a U-100 syringe, rounded to one decimal place. Select one to open the calculator with that vial, water, and dose filled in.

The 0.25 mg dose runs from 2.5 units (10 mg with 1 mL) to 37.5 units (2 mg with 3 mL), fifteen times apart. At the top of the range a 2 mg vial runs short: mixed with 3 mL, 1 mg is 150 units and needs two draws, and the vial holds less than one 2.4 mg dose.

A 5 mg vial with 2 mL (2.5 mg/mL) puts the starting dose at 10 units, a whole mark on any insulin syringe, and keeps every dose up to 2.4 mg under 100 units.

How many full doses a vial holds depends only on the vial size and the dose. The water volume changes the units per dose, but the milligrams in the vial stay the same.

The four starting weeks use only 1 mg, so a 10 mg vial holds 40 doses of 0.25 mg. In practice a little liquid stays behind, so the last dose can come up short.

Storage ends most vials sooner. The CDC says to discard an opened multi-dose vial within 28 days unless the manufacturer gives another date. Four weekly doses fit in that window, so at 0.25 mg a 10 mg vial would be thrown out with 9 mg still in it. A 2 mg vial wastes less: the same four weeks leave 1 mg behind.

The last column is how much a misread of half a unit mark changes the 0.25 mg dose, as a share of the whole.

At 10 mg/mL the starting dose is only 2.5 units. That sits between two marks on most 30 unit syringes and between two 2 unit marks on a 1 mL syringe, and half a unit off is a fifth of the dose.

A weak mix is easier to read but uses more liquid as the doses climb. At 1 mg/mL (2 mg with 2 mL) the starting dose is 25 units and a half-unit slip is 2% of it, but 1 mg is already a full 100 units. Mixes from 2 to 2.5 mg/mL put 0.25 mg at 10 to 12.5 units, and every dose the vial can supply still fits in one draw.

For draws under 30 units, a 30 unit syringe has 1 unit marks, and some brands add half marks. The syringe units blog compares barrel sizes, and the BAC water volume blog covers how the water volume moves a dose along the scale.

In July 2024 the FDA warned about dosing errors with compounded semaglutide. Patients in the reports injected five to 20 times the intended dose, mostly by drawing too much from a multi-dose vial. The agency pointed to mix-ups between milligrams, millilitres, and units. The reported cases follow a few patterns:

• Patients told to draw 5 units (0.05 mL) on a 1 mL syringe drew to 50 units instead.
• A provider meant 0.25 mg, which was 5 units at that strength, and prescribed 25 units, five times the dose.
• Another provider wrote 20 units where 2 units was intended, and three patients received ten times the dose.
• A patient who was also a health care provider recalculated their own dose in units and injected ten times the intended amount.

The same slip happens at home when a unit count moves from one vial to another. Twenty five units is 0.25 mg from a 2 mg vial with 2 mL, and 2.5 mg, ten times as much, from a 10 mg vial with 1 mL.