You bought a vial of lyophilized peptide powder. Now you need to turn it back into a liquid you can actually inject. This is called reconstitution, and it's simpler than it looks, but there are a few things you can screw up if you're not paying attention.
What is bacteriostatic water?
Bacteriostatic water (usually just called "bac water") is sterile water with 0.9% benzyl alcohol added as a preservative. The benzyl alcohol stops bacteria from growing, which is why it's the go-to solvent for reconstituting injectable peptides.
You're dissolving a freeze-dried powder back into liquid form so it can be drawn into a syringe and injected. That liquid needs to stay clean, not just when you mix it, but for the days or weeks you'll be pulling doses from the same vial. Bac water handles that.
It's sold in 30 mL vials at most pharmacies and medical supply stores. Cheap and easy to find. Buy USP-grade with proper labeling and skip anything sketchy.
Why you can't just use sterile water
Regular sterile water (water for injection) has no preservative. The moment you push a needle through a vial's rubber stopper, you've opened a path for contamination. Bac water's benzyl alcohol keeps bacteria from multiplying even after you've punctured the stopper a dozen times.
Plain sterile water works if you're mixing and injecting the entire vial in one shot. But most peptide protocols involve pulling multiple doses from one vial over days or weeks. Without a preservative, bacteria can colonize the solution. Injecting contaminated liquid causes infections.
Bottom line: if you're drawing more than one dose from a vial, use bacteriostatic water.
Equipment you'll need
Before you start, gather everything:
| Item | Purpose |
|---|---|
| Bacteriostatic water (USP grade) | Solvent for reconstitution |
| Alcohol swabs | Sterilize vial tops before piercing |
| Insulin syringes (1 mL / 100 unit) | Drawing and injecting doses |
| Mixing syringe (1-3 mL) | Drawing bac water for reconstitution |
| Peptide vial (lyophilized powder) | The peptide you're reconstituting |
| Sharps container | Safe needle disposal |
Insulin syringes are measured in "units" where 100 units = 1 mL. This becomes important when calculating doses.
Step-by-step reconstitution
1. Clean your workspace. Wash your hands. Work on a clean, flat surface. You're preparing an injectable, so basic hygiene matters.
2. Swab the vial tops. Use an alcohol swab on both the peptide vial and the bac water vial. Let them air dry for a few seconds.
3. Draw your bacteriostatic water. Using your mixing syringe, draw the desired amount of bac water. How much depends on your dosing math (covered below), but 1 mL or 2 mL are the most common amounts.
4. Inject the water into the peptide vial, gently. This is where people go wrong. Do not squirt the water directly onto the powder cake. Peptides are fragile molecules and a high-pressure stream of water can damage them. Angle the needle so the water runs slowly down the inside wall of the vial. Let gravity do the work.
5. Swirl, don't shake. Once the water is in the vial, gently roll or swirl it between your fingers. Never shake a peptide vial. Shaking creates foam and can denature the peptide (break apart its structure). Most peptides dissolve within a minute or two of gentle swirling. If you see small particles, set the vial down and wait. They'll usually dissolve on their own.
6. Inspect the solution. The reconstituted peptide should be clear or very slightly hazy. If it's cloudy, has visible particles that won't dissolve, or looks discolored, don't use it.
How to calculate your dose
The math is simple. You need three numbers:
- Total peptide in the vial (in mcg or mg)
- Amount of bac water you added (in mL)
- Your target dose (in mcg or mg)
The formula:
Dose volume = (target dose / total peptide) x total water added
Example
Say you have a 5 mg vial of BPC-157 and you add 2 mL of bac water. Your target dose is 250 mcg.
First, convert to the same units: 5 mg = 5,000 mcg.
Dose volume = (250 mcg / 5,000 mcg) x 2 mL = 0.1 mL
On a 100-unit insulin syringe, 0.1 mL = 10 units. So you'd draw to the "10" mark.
Quick reference for common reconstitution volumes with a 5 mg vial:
| Bac water added | Concentration | 250 mcg dose | 500 mcg dose |
|---|---|---|---|
| 1 mL | 5 mg/mL | 0.05 mL (5 units) | 0.1 mL (10 units) |
| 2 mL | 2.5 mg/mL | 0.1 mL (10 units) | 0.2 mL (20 units) |
| 2.5 mL | 2 mg/mL | 0.125 mL (12.5 units) | 0.25 mL (25 units) |
More water means larger injection volumes but easier-to-measure doses. Less water means smaller injections but requires more precision. 2 mL is a good middle ground.
The same math applies to any peptide. TB-500, Ipamorelin, Sermorelin. The formula is identical. Only the vial size and target dose change.
Storage after reconstitution
Once reconstituted, peptide solutions must be refrigerated at 2-8°C (36-46°F). Store vials upright in the fridge, away from light. Most reconstituted peptides stay stable for about 28 days in bac water when stored properly.
A few storage rules:
- Never freeze a reconstituted peptide. Freezing can damage the molecular structure.
- Keep it in the fridge, not on the counter. Room temperature accelerates degradation.
- Label the vial with the reconstitution date and concentration.
- Swab the stopper with alcohol before every draw.
Unreconstituted (lyophilized) peptide powder is much more stable. Most can sit in the freezer for months or years. Only reconstitute what you'll use within about a month.
Common mistakes
Blasting water onto the powder cake. The single most common error. High-pressure water can denature the peptide. Aim the needle at the glass wall and let the water trickle down.
Shaking the vial. Swirl. Roll. Tilt. Do not shake. Aggressive agitation damages peptide bonds and creates bubbles that make accurate dosing difficult.
Using too little water. If you're trying to measure 2 units on an insulin syringe, the margin of error is huge. Use enough bac water to make your doses easy to measure.
Skipping the alcohol swab. It takes three seconds. Every time you pierce the stopper, swab it first.
Storing at room temperature. Reconstituted peptides degrade fast outside the fridge. Even a few hours at room temp can reduce potency.
Reusing syringes. Insulin syringes are single-use. Reusing them increases infection risk and dulls the needle, making injections more painful.
Summary
Reconstitution feels complicated the first time and becomes routine by the third. Use bacteriostatic water (not plain sterile water), let it run down the side of the vial, do the dose math, refrigerate after mixing, and use within 28 days. The process is the same whether you're working with semaglutide, BPC-157, CJC-1295, or anything else.
Disclaimer: This article is for educational purposes only and does not constitute medical advice. Peptide therapies should be pursued under the guidance of a qualified healthcare provider. Never self-prescribe injectable medications. Dosages, protocols, and suitability vary based on individual health factors. Always consult your doctor before starting any new treatment.