Disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional before starting any injection therapy, changing your medication routine, or if you have any health concerns.

Australian regulatory note: Some peptides discussed in this guide (including BPC-157 and TB-500) are not TGA-approved for human therapeutic use in Australia. This guide explains reconstitution technique for patients who have been prescribed compounded peptides by a doctor, or who are handling such products under their prescriber's direction. Always follow your prescriber's specific protocol.

Most injectable peptides arrive as a freeze-dried (lyophilised) powder in a small glass vial. Before you can inject them, you need to dissolve the powder in a sterile liquid. This process is called reconstitution, and bacteriostatic water is the standard choice for it. The process is simple, but getting the details right matters: incorrect reconstitution can damage the peptide, create contamination risks, or lead to dosing errors.

This guide is general information, not a substitute for advice from your prescriber. If anything about your medication or technique is unclear, ring your prescribing doctor or call Healthdirect on 1800 022 222.

This guide covers everything you need to know about reconstituting peptides at home: what bacteriostatic water is, how much to add, the correct technique to preserve your peptide, and how to store the solution once it is mixed.

Peptide reconstitution supplies including peptide vial, bacteriostatic water, draw syringe, and insulin syringe — Peptide reconstitution supplies: lyophilised peptide vial, bacteriostatic water, 18G draw syringe, and insulin syringe.

Peptide reconstitution kit: vial of peptide powder, vial of bacteriostatic water, 18G blunt fill needle, 1mL insulin syringe, and alcohol prep wipes

1. What Is Bacteriostatic Water?

Bacteriostatic water (BAC water) is sterile water with 0.9% benzyl alcohol added as a preservative. The benzyl alcohol inhibits bacterial growth, which is critical for multi-dose use: once you puncture the vial's rubber stopper, you create a potential entry point for bacteria. BAC water keeps the reconstituted solution safe for multiple withdrawals over its usable life.

Why not regular sterile water? Plain sterile water for injection contains no preservative. Once opened, it must be used immediately or discarded. For peptides that you will dose from over multiple days or weeks, bacteriostatic water is the correct choice. BAC water extends the usable window to approximately 28 days when refrigerated.

Bacteriostatic water is available from medical suppliers and some pharmacies in Australia. Injection Supplies now stocks 10mL bacteriostatic water vials for reconstitution workflows.

2. What You Need

Peptide vial: Your lyophilised (freeze-dried) peptide. It should appear as a white or off-white powder or cake at the bottom of the vial.
Bacteriostatic water: A sealed, in-date vial of BAC water.
Draw syringe -- optional convenience for reconstitution: A 10ml draw syringe with 18G needle makes peptide reconstitution cleaner when you need to transfer a larger volume of bacteriostatic water (typically 2ml or more) into a lyophilised peptide vial -- you can move all the water in one single transfer rather than multiple passes. It's convenient, not required. You can do the same reconstitution using a 1ml insulin syringe if that's what you have on hand. If you go that route, use a fresh insulin syringe for each transfer -- don't re-puncture the vial stopper with the same needle. A dulled needle increases coring risk (shearing rubber fragments from the stopper into the vial).
Insulin syringe: A 1ml insulin syringe with 31G needle for drawing and injecting your individual doses after reconstitution.
Alcohol wipes: 70% isopropyl alcohol wipes for cleaning vial stoppers before every puncture.
Sharps container: For used needles and syringes.

3. How Much Water to Add

The amount of BAC water you add determines the concentration of your reconstituted peptide, which in turn determines how many units on the syringe equal your prescribed dose. This is the step where most mistakes happen.

The basic formula

Concentration (mg/ml) = peptide amount (mg) divided by water volume (ml)

For example: a 5mg peptide vial reconstituted with 2ml of BAC water gives you a concentration of 2.5mg/ml. If your prescribed dose is 250mcg (0.25mg), you need 0.1ml per injection, which equals 10 units on a standard 1ml insulin syringe.

Common reconstitution volumes

Peptide Amount	BAC Water Added	Concentration	250mcg Dose =
5mg	1ml	5mg/ml	5 units (0.05ml)
5mg	2ml	2.5mg/ml	10 units (0.1ml)
5mg	2.5ml	2mg/ml	12.5 units (0.125ml)
10mg	2ml	5mg/ml	5 units (0.05ml)
10mg	5ml	2mg/ml	12.5 units (0.125ml)

Choosing your volume: Adding more water makes dosing easier (larger volumes are easier to measure accurately on a syringe), but means you use more syringe capacity per dose. Adding less water concentrates the solution, which is useful if your dose volume would otherwise be very large. For most peptides in the 5-10mg range, 2ml of BAC water is a practical middle ground.

Your prescriber or compounding pharmacy may specify the reconstitution volume. If they do, follow their instructions exactly.

Wiping the rubber stopper of a medication vial with a 70% isopropyl alcohol prep wipe before drawing a dose

4. Step-by-Step Reconstitution

Step 1: Clean your workspace

Wash your hands thoroughly. Set out all supplies on a clean, flat surface. You want everything within reach before you start.

Step 2: Inspect the peptide vial

Before reconstituting: visually inspect the lyophilised peptide. The cake should be uniform and intact. Discoloration, loose powder, or a displaced cake may indicate transit damage or temperature excursion -- don't proceed; contact your supplier.

Step 3: Clean both vial stoppers

Wipe the rubber stopper on both the BAC water vial and the peptide vial with separate alcohol wipes. Let them air-dry for 10-15 seconds. Do not blow on them to speed drying.

Step 4: Draw the BAC water

Using an 18G draw syringe (faster): Pull the plunger back to draw in air equal to the volume of water you plan to add. Insert the needle into the BAC water vial, push the air in, invert, and draw your target volume. Remove the needle.

Using 1ml insulin syringes (works with what you likely have): Draw your target volume in one or more passes -- e.g., 2ml of BAC water takes two 1ml draws. Use a fresh insulin syringe for each transfer and discard each one before grabbing the next.

Step 5: Add water to the peptide vial (slowly)

This is the critical step. Insert the needle through the peptide vial's rubber stopper. Aim the needle at the inside wall of the vial, not directly at the powder. Slowly press the plunger to let the water trickle down the glass wall and pool at the bottom. Do not squirt the water directly onto the peptide powder.

Why this matters: Peptides are fragile molecules. Forceful streams of water can cause foaming and may denature (damage) the peptide's molecular structure. Gentle, wall-directed addition preserves the peptide's integrity.

Step 6: Let it dissolve

Do not shake the vial. Shaking creates bubbles and can damage the peptide through mechanical stress. Instead:

Gently swirl the vial in a slow circular motion, or
Roll the vial between your palms for 20-30 seconds, or
Simply let the vial sit undisturbed for 10-15 minutes. Most peptides dissolve on their own.

The solution should become completely clear and colourless. If particles remain floating after 30 minutes of gentle swirling, something may be wrong with the peptide. Do not use a solution that is cloudy or contains visible particles.

Step 7: Label the vial

Write on the vial or a small adhesive label: the peptide name, the reconstitution date, the concentration (e.g., "BPC-157 2.5mg/ml, reconstituted 10/04"), and the discard date (28 days from reconstitution). This prevents confusion, especially if you have multiple peptides.

5. Calculating Your Dose After Reconstitution

Once reconstituted, you draw your individual doses using an insulin syringe. The key is knowing how your syringe scale translates to your peptide concentration.

You can work out the volume with our dose volume calculator.

A standard 1ml insulin syringe is marked in 100 units, where 100 units = 1ml. So:

10 units = 0.1ml
25 units = 0.25ml
50 units = 0.5ml

Example dose calculation

Peptide: 5mg BPC-157, reconstituted with 2ml BAC water = 2.5mg/ml concentration.

If your prescribed dose is 250mcg (0.25mg):

Volume needed: 0.25mg divided by 2.5mg/ml = 0.1ml = 10 units on the syringe

If your dose is very small (under 5 units on a 1ml syringe), consider using a 0.5ml insulin syringe. It has the same 100-unit markings across 0.5ml, so each unit mark represents 0.005ml instead of 0.01ml, giving you twice the precision for small doses.

For a detailed explanation of syringe markings and how to read them accurately, see our How to Read an Insulin Syringe guide.

6. Storage and Shelf Life

Refrigerate immediately after reconstitution. Store at 2-8°C.
Refrigeration without freezing is the standard guidance for most reconstituted peptides. Some research protocols freeze reconstituted peptides successfully -- defer to the specific guidance that came with your product.
Protect from light. Some peptides are light-sensitive. Keep the vial in a dark area of the refrigerator or wrap it in foil.
28-day maximum. Discard reconstituted peptide solutions after 28 days, even if liquid remains. The bacteriostatic preservative's effectiveness diminishes over time, and the risk of bacterial contamination increases.
Always clean the stopper with an alcohol wipe before each withdrawal. Every needle puncture is a potential contamination event.
Inspect before each use. The solution should remain clear and colourless. If it becomes cloudy, changes colour, or develops visible particles, discard it.

Storing unreconstituted peptides

Lyophilised (powder) peptides are more stable than reconstituted ones. Most can be stored in the refrigerator for months or in the freezer for longer. Check the specific storage instructions from your supplier. Do not reconstitute peptides until you are ready to begin using them.

7. Common Mistakes

Squirting water directly onto the powder

The most common reconstitution mistake. A direct stream of water creates force that can damage peptide molecules and cause excessive foaming. Always aim the water stream at the vial wall and let it trickle down gently.

Shaking the vial

Shaking causes foaming and can denature the peptide through mechanical stress. Swirl gently or let the vial sit. Patience here protects your investment.

Using the wrong type of water

Tap water, distilled water, and saline are not appropriate substitutes. Use bacteriostatic water for multi-dose reconstitution.

Inaccurate water measurement

If you add more or less water than intended, your concentration changes and every subsequent dose will be wrong. Measure carefully using a syringe with clear volume markings. A 3ml or 5ml syringe is easier to measure accurately than a 10ml syringe for volumes under 3ml.

Not labelling the vial

After a week in the refrigerator, reconstituted vials can look identical. Unlabelled vials lead to confusion about concentration, reconstitution date, and which peptide is which. Label immediately after reconstituting.

Keeping reconstituted peptides too long

The 28-day limit exists for a reason. Even with bacteriostatic water's preservative, bacterial risk increases over time. If you are not going to use the entire vial within 28 days, reconstitute with less water to create a more concentrated solution, or use a smaller peptide vial size.

When to call your prescriber

Most injections go smoothly - a small drop of blood or a brief sting are normal. The list below covers things that aren't normal and warrant a phone call to your prescriber:

Redness, warmth or pus at the injection site that develops over 24-72 hours
A hard lump that doesn't go away after a week, or one that's hot and tender
Fever, chills or feeling unwell after an injection
Any rash, hives or itching at or beyond the injection site (possible allergic reaction)
Signs of a severe allergic reaction - swelling of face or throat, difficulty breathing - call 000 immediately
You realise you injected from a vial that had been left out, was cloudy or contained particles

Frequently Asked Questions

What is the difference between bacteriostatic water and sterile water?

Bacteriostatic water contains 0.9% benzyl alcohol as a preservative that inhibits bacterial growth. Sterile water contains no preservative. BAC water is safe for multi-dose use (up to 28 days refrigerated); sterile water must be used immediately and any remainder discarded. For peptides that you will dose from over multiple days or weeks, bacteriostatic water is the correct choice.

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

There is no single correct answer because it depends on your desired concentration and dose. Common choices are 1ml (giving 5mg/ml) or 2ml (giving 2.5mg/ml). More water means easier, more precise dosing; less water means more concentrated solution and smaller injection volumes. Your prescriber may specify a volume. If not, 2ml is a practical default for most 5mg peptide vials.

Can I use bacteriostatic water for semaglutide?

Compounded semaglutide from a compounding pharmacy is typically supplied already in solution (pre-reconstituted). You draw directly from the vial without needing to add water. If your semaglutide arrives as a lyophilised powder, follow the compounding pharmacy's specific reconstitution instructions, which may specify BAC water or a different diluent.

What syringe do I use to add the bacteriostatic water?

You can use an 18G draw syringe or multiple insulin-syringe transfers. An 18G draw syringe is convenient when adding 2ml or more of BAC water -- you move all the water in one pass. If you use insulin syringes instead, use a fresh one for each transfer. Do not re-puncture the peptide vial stopper with the same needle twice.

My peptide did not dissolve completely. Is it still good?

Give it time. Some peptides take 15-30 minutes to dissolve fully. Gently swirl every few minutes. If particles remain floating after 30 minutes, the peptide may have been damaged (by heat, shaking, or age). Do not inject a solution with visible particles. Contact your supplier.

Can I store reconstituted peptides in the freezer?

Manufacturer guidance for most reconstituted peptides is refrigeration without freezing. Some research protocols freeze reconstituted peptides successfully -- defer to the specific guidance that came with your product. Only unreconstituted (powder form) peptides are routinely frozen for long-term storage.