How much BAC water do I add to a 2mg semaglutide vial?

The most common approach is 2 mL of BAC water, which gives a 1 mg/mL concentration. This makes dose calculations simple: 0.25 mg = 25 units, 0.5 mg = 50 units on a U100 insulin syringe.

Can I use sterile water instead of bacteriostatic water?

You can, but bacteriostatic water (which contains benzyl alcohol as a preservative) is strongly preferred. It extends the stable life of reconstituted peptides and inhibits bacterial growth over the 28-day usage period.

How long does reconstituted semaglutide last?

When stored in the refrigerator at 2-8°C, reconstituted semaglutide is generally stable for up to 28 days. Always check the vial for cloudiness or particulates before each use.

What syringe should I use for semaglutide?

Use U100 insulin syringes (28-31 gauge, 0.3 mL or 0.5 mL). The 100-unit scale matches the math from a 1 mg/mL concentration: 0.1 mg = 10 units, 0.25 mg = 25 units, etc.

Why did my semaglutide turn cloudy?

Cloudiness indicates degradation or contamination. This can happen from shaking the vial, temperature fluctuations, or contamination during reconstitution. Discard the vial and do not use it.

How to Reconstitute Semaglutide: Step-by-Step Guide

Semaglutide comes as a lyophilized (freeze-dried) powder that must be mixed with bacteriostatic water (BAC water) before use. Getting this process right ensures accurate dosing and longer vial stability.

What You Need Before You Start

Semaglutide vial (typically 2mg, 3mg, 5mg, or 10mg)
Bacteriostatic water (BAC water) for injection
Insulin syringes (0.3 mL or 0.5 mL, 100-unit scale)
Alcohol swabs
A refrigerator for storage

Choosing the Right BAC Water Volume

The amount of BAC water you add determines your final concentration. A common target is 1 mg/mL, which makes dose math straightforward. For example, adding 2 mL to a 2 mg vial gives you exactly 1 mg/mL.

Use the PeptiTools calculator to enter your vial size and desired concentration. The calculator will show exactly how many units to draw for any dose, removing the guesswork entirely.

Tip: Always inject BAC water slowly against the glass wall of the vial, not directly onto the powder. Swirl gently to dissolve. Never shake.

Step-by-Step Reconstitution

Wipe the top of both the semaglutide vial and BAC water vial with alcohol swabs. Allow to dry.
Draw the appropriate amount of BAC water into your syringe.
Insert the needle into the semaglutide vial at a 45-degree angle.
Slowly inject the BAC water along the inner wall of the vial.
Gently swirl (do not shake) until the powder is fully dissolved.
The solution should be clear and colorless. Discard if cloudy or discolored.
Label the vial with the date of reconstitution.

Common Concentration Examples

Here are the most common BAC water volumes for standard vial sizes:

2 mg vial + 2 mL BAC water = 1 mg/mL (100 mcg per 10 units on a U100 syringe)
3 mg vial + 3 mL BAC water = 1 mg/mL
5 mg vial + 2.5 mL BAC water = 2 mg/mL (200 mcg per 10 units)
10 mg vial + 2 mL BAC water = 5 mg/mL (500 mcg per 10 units)

Using the PeptiTools Calculator

Instead of doing the math manually, use the free PeptiTools peptide reconstitution calculator. Enter your vial size (mg), how much BAC water you added (mL), and your target dose (mcg or mg). The calculator instantly shows you the exact number of units to draw on your syringe, with a live diagram.

Semaglutide CalculatorPre-loaded with typical semaglutide vial sizes and starting doses.

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General Peptide CalculatorEnter any vial size and concentration for a custom calculation.

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Storage After Reconstitution

Reconstituted semaglutide should be refrigerated at 36-46°F (2-8°C) immediately after mixing. It remains stable for up to 28 days when refrigerated. Do not freeze reconstituted peptides, as this can degrade the compound.

Semaglutide vs Other GLP-1 Peptides

Semaglutide is a GLP-1 receptor agonist. Tirzepatide adds GIP receptor activity, and retatrutide goes further with GLP-1, GIP, and glucagon receptor activity. Each compound has its own typical vial sizes, concentration targets, and dose ranges.

Tirzepatide Reconstitution GuideKey differences in concentration strategy and titration schedule.

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Tirzepatide Peptide PagePre-tuned calculator with Mounjaro/Zepbound dosing protocol.

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Retatrutide Peptide PageTriple agonist with the highest clinical weight loss data to date.

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