Semaglutide Reconstitution: How Much Bacteriostatic Water

A 5 mg vial of Semaglutide reconstituted with 2 mL of bacteriostatic water gives 2.5 mg/mL, a 10 mg vial with 2 mL gives 5 mg/mL, and a 20 mg vial with 4 mL gives 5 mg/mL. The calculation depends only on the quantity in the vial and the volume of water added, so the figures below apply to any Semaglutide vial of those sizes.

There is no single correct volume. Adding more water does not change how much is in the vial. It spreads the same quantity through a larger volume, which changes how many syringe units correspond to a given amount. The tables on this page use volumes that produce round numbers on a U-100 syringe; other volumes work identically as long as the resulting concentration is written on the vial.

Peptide reconstitution calculator

Set to this vial below. Change the vial size, water volume, amount or syringe and it recalculates the concentration and the syringe units. For laboratory research use only.

Desired dose

0.5 mg 1 mg 1.5 mg 2 mg 2.5 mg 3 mg 3.5 mg 4 mg 4.5 mg 5 mg Custom… Milligrams (mg) Micrograms (mcg)

1 mg = 1000 mcg

Research peptide in vial (mg) 5 mg 10 mg 20 mg 30 mg Custom… As printed on the vial

Bacteriostatic water added (ml) 1 mL 2 mL 3 mL Custom… Total volume you put in the vial

Syringe size 0.3 ml — 30 units 0.5 ml — 50 units 1.0 ml — 100 units Custom…

Draw to 5.0units

Concentration—

Volume per dose—

Doses per vial—

All products are sold strictly for laboratory research use only and are not for human or veterinary consumption. This calculator is provided as a general reference tool.

How much bacteriostatic water for 5 mg Semaglutide?

A 5 mg Semaglutide vial is commonly reconstituted with 2 mL of bacteriostatic water, which gives 2.5 mg/mL; 1 mL gives 5 mg/mL, 2.5 mL gives 2 mg/mL and 5 mL gives 1 mg/mL. At 2.5 mg/mL each 0.1 mL of solution contains 0.25 mg.

Water added	Concentration	Amount in 0.1 mL (10 units on a U-100 syringe)
1 mL	5 mg/mL	0.5 mg
2 mL	2.5 mg/mL	0.25 mg
2.5 mL	2 mg/mL	0.2 mg
5 mL	1 mg/mL	0.1 mg

How much bacteriostatic water for 10 mg Semaglutide?

A 10 mg Semaglutide vial is commonly reconstituted with 2 mL of bacteriostatic water, which gives 5 mg/mL; 1 mL gives 10 mg/mL, 4 mL gives 2.5 mg/mL and 5 mL gives 2 mg/mL. At 5 mg/mL each 0.1 mL of solution contains 0.5 mg.

Water added	Concentration	Amount in 0.1 mL (10 units on a U-100 syringe)
1 mL	10 mg/mL	1 mg
2 mL	5 mg/mL	0.5 mg
4 mL	2.5 mg/mL	0.25 mg
5 mL	2 mg/mL	0.2 mg

How much bacteriostatic water for 20 mg Semaglutide?

A 20 mg Semaglutide vial is commonly reconstituted with 4 mL of bacteriostatic water, which gives 5 mg/mL; 2 mL gives 10 mg/mL and 5 mL gives 4 mg/mL. At 5 mg/mL each 0.1 mL of solution contains 0.5 mg, the same concentration as a 10 mg vial with 2 mL.

Water added	Concentration	Amount in 0.1 mL (10 units on a U-100 syringe)
2 mL	10 mg/mL	1 mg
4 mL	5 mg/mL	0.5 mg
5 mL	4 mg/mL	0.4 mg

For any other volume, the calculator on this page works out the concentration. Before choosing a larger volume, check that the vial has headspace for it. One multi-dose vial of bacteriostatic water covers several research vials.

Reading the concentration on a U-100 syringe

A U-100 insulin syringe is graduated in units, and 100 units equal 1 mL. Units are therefore millilitres multiplied by 100: 0.1 mL is 10 units and 0.25 mL is 25 units. A 0.5 mL syringe carries 50 units and a 0.3 mL syringe carries 30 units on the same scale, with finer markings that make small volumes easier to read.

To find the volume that contains a given amount, divide the amount by the concentration. At 2.5 mg/mL (a 5 mg vial with 2 mL of water), the volume that contains 0.25 mg is 0.25 divided by 2.5, which is 0.1 mL, or 10 units. The table below runs the same calculation for four arbitrary amounts. They illustrate the arithmetic and nothing else.

Amount (illustrative)	Volume at 2.5 mg/mL	U-100 units
0.1 mg	0.04 mL	4 units
0.25 mg	0.1 mL	10 units
0.5 mg	0.2 mL	20 units
1 mg	0.4 mL	40 units

Volumes below about 0.1 mL are hard to read accurately on a 1 mL syringe. Either move to a 0.3 mL or 0.5 mL syringe, or reconstitute with more water so that the same mass occupies a larger, more legible volume.

The Semaglutide vial

Semaglutide is commonly supplied in research catalogues as 5 mg, 10 mg and 20 mg lyophilised vials. Vistara Labs does not currently stock Semaglutide, but you can request it: contact us and we will source it for you. The calculator on this page works for any vial. The same arithmetic for a related incretin peptide is set out in tirzepatide reconstitution.

What Semaglutide is

Semaglutide is a glucagon-like peptide 1 (GLP-1) analogue with an extended half-life of approximately one week. Its human research includes large randomised trials of metabolic and cardiovascular outcomes.

• In the STEP 1 trial of 1961 adults with overweight or obesity and without diabetes, the mean weight change at 68 weeks was -14.9% with Semaglutide against -2.4% with placebo (Wilding et al., 2021).
• In the SUSTAIN-6 trial of 3297 people with type 2 diabetes at high cardiovascular risk, the composite of cardiovascular death, nonfatal myocardial infarction or nonfatal stroke occurred in 6.6% with Semaglutide and 8.9% with placebo (Marso et al., 2016).
• In the SELECT trial of 17,604 people with cardiovascular disease and overweight or obesity but no diabetes, the same composite outcome occurred in 6.5% with Semaglutide and 8.0% with placebo, a hazard ratio of 0.80 (Lincoff et al., 2023).

Reconstitution technique

Let the vial reach room temperature, swab both stoppers, and run the measured water slowly down the inside wall of the vial rather than onto the powder. Swirl or tilt gently until the cake dissolves, never shake, and give any remaining powder a few minutes to settle into solution. Label the vial with the date and the concentration, then keep it refrigerated at 2 to 8 °C and protected from light. The full method, with the reason behind each step, is in how to reconstitute peptides with bacteriostatic water.

Why the solution should look clear

Properly reconstituted Semaglutide forms a clear, colourless solution. Cloudiness, strands or a gel that will not disperse usually mean the water went in too fast or the vial was shaken; haze that appears later points to warm or bright storage. The causes are covered in why peptides gel or go cloudy.

Bacteriostatic water, not sterile water

Bacteriostatic water is sterile water with 0.9% benzyl alcohol, a preservative that allows a refrigerated vial to be accessed more than once; plain sterile water is intended for single access. The difference is explained in bacteriostatic water explained.

Frequently asked questions

How much bac water for a 5 mg Semaglutide vial?

A 5 mg Semaglutide vial is commonly reconstituted with 2 mL of bacteriostatic water, which gives 2.5 mg/mL; 5 mL gives 1 mg/mL. At 2.5 mg/mL each 0.1 mL (10 units on a U-100 syringe) contains 0.25 mg.

How much bac water for a 10 mg Semaglutide vial?

A 10 mg Semaglutide vial is commonly reconstituted with 2 mL of bacteriostatic water, which gives 5 mg/mL; 5 mL gives 2 mg/mL. At 5 mg/mL each 0.1 mL (10 units on a U-100 syringe) contains 0.5 mg.

How much bac water for a 20 mg Semaglutide vial?

A 20 mg Semaglutide vial is commonly reconstituted with 4 mL of bacteriostatic water, which gives 5 mg/mL; 5 mL gives 4 mg/mL. At 5 mg/mL each 0.1 mL (10 units on a U-100 syringe) contains 0.5 mg.

How many units on a U-100 syringe contain 0.25 mg at 2.5 mg/mL?

At 2.5 mg/mL (a 5 mg vial with 2 mL of water), the volume that contains 0.25 mg is 0.25 divided by 2.5, which is 0.1 mL, or 10 units. Units are millilitres multiplied by 100, so 0.1 mL is 10 units. The amounts on this page illustrate the arithmetic only.

What should reconstituted Semaglutide look like?

Properly reconstituted Semaglutide forms a clear, colourless solution. Cloudiness, strands or a gel that will not disperse usually mean the water went in too fast or the vial was shaken; haze that appears later points to warm or bright storage. More on the causes in why peptides gel or go cloudy.

Can I use sterile water instead of bacteriostatic water?

Only for a vial that will be accessed once. Bacteriostatic water is sterile water with 0.9% benzyl alcohol, a preservative that allows a refrigerated vial to be accessed more than once; plain sterile water is intended for single access. Details in bacteriostatic water explained.

How should a reconstituted Semaglutide vial be stored?

Refrigerated at 2 to 8 °C, protected from light and labelled with the date and the concentration. Unopened lyophilised vials are kept cold and dark until they are needed. The full storage guide is how to store research peptides.

Work it out for a different vial or concentration

Our peptide calculator opens pre-set for a 5 mg vial with 2 mL of water and marks the 0.25 mg draw of 10 units on a syringe diagram. Change the vial size, water volume, amount or syringe and it recalculates.

For any vial: bacteriostatic water.

Related reading. How to reconstitute peptides, how to store research peptides and bacteriostatic water explained.

Sources: Wilding JPH et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity. N Engl J Med. 2021. PMID 33567185. Marso SP et al. Semaglutide and Cardiovascular Outcomes in Patients with Type 2 Diabetes. N Engl J Med. 2016. PMID 27633186. Lincoff AM et al. Semaglutide and Cardiovascular Outcomes in Obesity without Diabetes. N Engl J Med. 2023. PMID 37952131.