How to Reconstitute Semaglutide: Water and Units Chart for 5, 10 and 15 mg Vials

A semaglutide vial that has been mixed wrongly looks exactly like one mixed right, which is why reconstitution is where dosing mistakes stay silent. The water you add does not change how much semaglutide is in the vial. It changes the concentration, and so how many units on the syringe a given dose reads. FDA has a safety alert on exactly this: with compounded semaglutide in multiple-dose vials, confusion between millilitres, milligrams and units led some patients to inject five to 20 times the intended dose. In one report a dose meant to be 5 units (0.05 mL) was drawn as 50 units.

The formula and the syringe

A U-100 insulin syringe is marked so that 100 units is 1 mL; insulin products such as Humulin R are labelled 100 units/mL (U-100). Three steps turn any vial into a syringe mark:

• Concentration (mg/mL) = vial size (mg) divided by water added (mL).
• Volume (mL) = dose (mg) divided by concentration (mg/mL).
• Units = volume (mL) times 100.

So at 5 mg/mL every 20 units is 1 mg, and at 2.5 mg/mL every 40 units is 1 mg. A U-40 syringe reads the same volume 2.5 times differently, so check the barrel before you draw.

Semaglutide reconstitution chart

The vial sizes are the ones in the Bureau's own price tracker: research vials of 5, 10 and 15 mg (price data, readings to 1 November 2026). The doses are the label steps: 0.25, 0.5, 1, 1.7 and 2.4 mg for Wegovy and 2 mg, the top Ozempic dose. Values are rounded to one decimal place; a starred value is over 100 units, more than a 1 mL syringe holds.

5 mg vial

With 2 mL a 5 mg vial is 2.5 mg/mL: the 0.25 mg starting step is 10 units and 1 mg is 40 units.

10 mg vial

A 10 mg vial with 2 mL is 5 mg/mL, the same strength as a 5 mg vial with 1 mL: 0.25 mg is 5 units, 1 mg is 20 units and 2.4 mg is 48 units.

15 mg vial

* More than 100 units. With 1 or 2 mL a 15 mg vial is so strong that the starting doses fall below 7 units, too fine to read reliably; 3 mL (5 mg/mL) gives the same readings as the 10 mg vial with 2 mL. Cells such as 3.3 or 6.7 fall between syringe marks, so the real draw there is approximate.

Choosing a water volume

As a Bureau rule of thumb, not a regulatory standard, pick the water so your usual dose lands between about 10 and 60 units. Below 10 units the marks are too close together to read well, and above 60 the injection volume grows. Semaglutide doses are small, so the low end is the problem: at 5 mg/mL the 0.25 mg step is only 5 units, while at 2.5 mg/mL it is 10. Because the doses climb about tenfold from 0.25 to 2.4 mg, no single concentration keeps every step in that window. Many readers mix the first vial weaker for the low steps and a later vial stronger. Whatever you choose, write the concentration on the vial and recalculate for every new vial, because the same units mean different milligrams at a different concentration.

How many weekly doses a vial holds

Whole doses only: vial size divided by dose, rounded down, ignoring overfill and the small loss in the needle.

The count matters because of time, not just milligrams. FDA's page on unapproved GLP-1 drugs (content current 1 October 2026) says vials holding multiple doses of a sterile medication should generally be used within 28 days after first use, because the risk of contamination rises after that, and that the vial should be discarded at 28 days even if medication remains. At one dose a week that is four doses. A 5 mg vial at the 0.25 mg step holds 20 weeks of doses, so most of it would sit far past that window. That is why a small vial, or less water and a shorter plan, makes more sense at the low steps, and why semaglutide cost is better read per dose than per vial.

What you need

• The vial, sealed, with a lot number that matches the certificate you were sent. The testing guide explains what a certificate can and cannot show. When researchers bought semaglutide online without a prescription, the vials held 28.6 to 38.7 percent more than the label stated and every sample carried endotoxin (J Med Internet Res 2024), so the label strength in the chart is itself an assumption.
• Bacteriostatic water. The Hospira label describes Bacteriostatic Water for Injection as sterile water with 0.9 percent (9 mg/mL) or 1.1 percent benzyl alcohol as a bacteriostatic preservative, in a multiple-dose container from which repeated withdrawals may be made. Plain sterile water has no preservative, and the label says benzyl alcohol products must not be used in neonates.
• A 3 mL syringe for the water and U-100 insulin syringes for doses.
• Alcohol pads and a marker for the vial label.

The mixing sequence

These steps are common practice among research peptide users, not a manufacturer procedure. Ozempic and Wegovy are not mixed at all: the Ozempic label lists pens holding a ready-made solution (2, 4 or 8 mg in 3 mL) and the Wegovy label single-dose pens and syringes plus a four-dose FlexTouch pen, all dosed in milligrams, never in units.

1. Let a refrigerated vial come to room temperature.
2. Wipe both stoppers with alcohol and let them air dry.
3. Draw the planned volume of bacteriostatic water and push out any air with the needle pointing up.
4. Angle the needle at the glass wall so the water runs down the inside instead of hitting the powder directly.
5. Let it dissolve, and swirl gently rather than shaking if powder remains.
6. Check it: it should be clear with no particles. Do not use a cloudy vial or one with particles.
7. Write the concentration in mg/mL and the date on the vial straight away.
8. Refrigerate it.

After mixing: storage

The Bureau found no published stability data for semaglutide powder reconstituted with bacteriostatic water, so we give no number of weeks. The branded pens' in-use times (56 days for an opened Ozempic pen) belong to buffered, preserved, tested solutions and do not transfer to a research vial. One laboratory study found semaglutide degrades faster in solution between pH 4.5 and 5.5 (J Pept Sci 2025); bacteriostatic water is labelled pH 5.7 (4.5 to 7.0), while the branded products are buffered near pH 7.4. Use the 28 day multiple-dose rule above as the conservative reference. How the branded pens are stored is on their labels, covered in does Ozempic need to be refrigerated and does Wegovy need to be refrigerated; how long a vial of bacteriostatic water itself lasts once opened is in bac water storage. Drawing technique and site rotation are in where to inject semaglutide.

Mistakes that actually happen

• Reading milligrams as units, or units as millilitres. The FDA alert describes a prescriber who meant 0.25 mg (5 units) and wrote 25 units, and another who wrote 20 units instead of 2. Convert from milligrams once, write the result in units on the vial, and keep the syringe size close to the dose.
• Reusing a unit count across vials. 20 units is 1 mg from a 5 mg/mL vial and 0.5 mg from a 2.5 mg/mL vial.
• Confusing syringes. U-100 and U-40 syringes look alike and read the same volume 2.5 times differently.
• Mixing before deciding the dose range. The right water volume depends on the steps you plan to run; the Ozempic and Wegovy dosage chart sets out the label schedule week by week.

Other GLP vials mix the same way but need different concentrations because the doses differ: see how to reconstitute retatrutide and tirzepatide units to mg. For general mixing of other peptides, how to reconstitute peptides covers the method, and compounded semaglutide explains how pharmacy vials differ from research vials.

Frequently asked questions

How much bacteriostatic water do I add to a 5 mg vial of semaglutide?

There is no single right amount; the water sets the concentration. With 2 mL the vial is 2.5 mg/mL, so 0.25 mg is 10 units and 1 mg is 40 units on a U-100 syringe. With 1 mL it is 5 mg/mL, which halves those readings to 5 and 20 units.

How much bacteriostatic water for a 10 mg semaglutide vial?

With 2 mL a 10 mg vial is 5 mg/mL: 0.25 mg is 5 units, 1 mg is 20 units and 2.4 mg is 48 units. With 3 mL it is 3.33 mg/mL, so 0.25 mg is 7.5 units and 1 mg is 30 units. Write the concentration on the vial once it is mixed.

How many units is 0.25 mg of semaglutide?

It depends on the concentration. At 2.5 mg/mL it is 10 units, at 5 mg/mL it is 5 units and at 10 mg/mL it is 2.5 units. The formula is dose in mg times water in mL times 100, divided by the vial size in mg.

How long does reconstituted semaglutide last?

The Bureau found no published stability data for reconstituted research semaglutide, so any number of weeks would be a guess. FDA's general recommendation for vials holding multiple doses of a sterile medication is to use them within 28 days after first use, which is four weekly doses.

Do Ozempic or Wegovy pens need to be reconstituted?

No. The branded pens and syringes hold a ready-made solution, so nothing is mixed and no water is added. Reconstitution only applies to vials of freeze-dried powder, which are not the FDA-approved products.

Can I use sterile water instead of bacteriostatic water?

Bacteriostatic water for injection is sterile water with a preservative, 0.9 percent or 1.1 percent benzyl alcohol on the Hospira label, in a multiple-dose container meant for repeated withdrawals. Plain sterile water has no preservative. The label also says benzyl alcohol products must not be used in neonates.

Sources (checked 7 November 2026)

1. Wegovy prescribing information, Novo Nordisk, revised 6/2026 (escalation 0.25, 0.5, 1, 1.7 mg, then 1.7 or 2.4 mg, 7.2 mg maximum; pen strengths). Checked 7 November 2026.
2. Ozempic prescribing information, Novo Nordisk, revised 5/2026 (0.25 mg to 2 mg; pen strengths; 56 day in-use time). Checked 7 November 2026.
3. FDA, dosing errors associated with compounded injectable semaglutide products, 26 July 2024. Checked 7 November 2026.
4. FDA, FDA’s Concerns with Unapproved GLP-1 Drugs Used for Weight Loss, content current 1 October 2026 (28 day rule; research-label warnings). Checked 7 November 2026.
5. Humulin R prescribing information, DailyMed (U-100 means 100 units/mL). Checked 7 November 2026.
6. Bacteriostatic Water for Injection, USP (Hospira) label, DailyMed (benzyl alcohol 0.9 or 1.1 percent, multiple-dose, pH 5.7). Checked 7 November 2026.
7. Malgave A et al. Semaglutide degradation by pH and temperature. J Pept Sci 2025;31(8):e70039. Checked 7 November 2026.
8. Ashraf AR et al. Semaglutide bought online without prescription: content, purity and endotoxin. J Med Internet Res 2024;26:e65440. Checked 7 November 2026.

Doses are the label steps from the Wegovy label revised June 2026 and the Ozempic label revised May 2026; vial sizes are from the Bureau price tracker, readings to 1 November 2026. Labels and trial records change; the leaflet in your box and your prescriber come first. Educational content, not medical advice.