Important: Most research peptides are not approved by the FDA for human use and are sold in the US for laboratory research purposes only. This guide explains the mechanics of reconstitution — it is not medical advice and the example doses below are illustrative math, not dosing recommendations. Consult a licensed healthcare professional before using any research compound.
Most research peptides ship as a lyophilized (freeze-dried) powder, because the dry powder is far more stable in transit than a liquid. Before that powder can be measured, it has to be turned back into a solution — that step is called reconstitution. Done correctly it takes about two minutes; done wrong, you can degrade the peptide or, worse, draw the wrong amount because your concentration math was off.
This guide covers what you need, the exact step-by-step method, the concentration formula, and a mg-by-mg BAC water chart so you can look up the answer for a 5 mg, 10 mg, or 30 mg vial without doing arithmetic. To skip the math entirely, run your numbers through the Peptide Reconstitution Calculator.
What "reconstitution" actually means#
Reconstitution is dissolving a dry peptide cake in a sterile liquid (the diluent) so it becomes an injectable, measurable solution. The peptide itself doesn't change — you're just rehydrating it. What you control is the concentration: how many milligrams of peptide end up in each milliliter of liquid. Concentration is what determines how far you pull the syringe for a given dose, so getting it right is the whole game.
What you need#
| Item | Why |
|---|---|
| Lyophilized peptide vial | The compound you're reconstituting |
| Bacteriostatic water (BAC water) | The diluent — see the next section on why BAC, not plain water |
| 1 mL / 100-unit insulin syringe | For drawing doses (small, fine needle) |
| A larger syringe + needle (optional) | 3 mL with an 18–21 g needle makes adding water easier |
| Alcohol prep pads | To swab both vial stoppers |
| A clean, flat workspace | Reduces contamination risk |
BAC water vs sterile water — which diluent?#
This trips up most first-timers. The two common diluents are not interchangeable:
- Bacteriostatic water (BAC water) is sterile water with 0.9% benzyl alcohol added as a preservative. The benzyl alcohol suppresses bacterial growth, so a reconstituted vial stays usable for weeks in the fridge. This is the standard choice for any vial you'll use across multiple doses. (Bacteriostatic Water for Injection, USP label)
- Sterile water for injection has no preservative. It's single-use — once opened or mixed, it has no protection against microbial growth.
Safety note: Benzyl alcohol — the preservative in BAC water — has been linked to "gasping syndrome" in newborns and low-birth-weight infants, and preservative-containing water should not be used to prepare medications for neonates. (benzyl alcohol toxicity / gasping syndrome)
Practically: for the multi-dose vials most people reconstitute, BAC water is the default.
How to reconstitute peptides: step by step#
- Equilibrate. Let the peptide vial and BAC water reach room temperature (about 10–20 minutes). Adding cold water to a cold cake slows dissolution.
- Sanitize. Wash your hands. Swab the rubber stopper on both the peptide vial and the BAC water vial with a fresh alcohol pad and let them air-dry.
- Draw your water. Using a syringe, draw up the exact volume of BAC water you calculated (see the chart below or use the calculator).
- Add it slowly, down the wall. Insert the needle at a slight angle and let the water run down the inside wall of the vial — never blast it directly onto the powder cake. Shear force from a hard stream can break peptide bonds. (peptide formulation handling, PMC)
- Dissolve gently — do not shake. Remove the syringe and swirl or gently roll the vial between your fingers until the solution is clear. Shaking introduces shear and foam that can denature the peptide. If foam forms, wait for it to settle. (protein drug stability, Nat Rev Drug Discov)
- Inspect. The finished solution should be completely clear with no floating particles or cloudiness. If it stays cloudy or has visible bits, don't use it.
- Label and refrigerate. Note the date and concentration on the vial and store it at 2–8 °C.
Calculating concentration (the only formula you need)#
Concentration is just peptide mass divided by water volume:
Concentration (mg/mL) = peptide (mg) ÷ BAC water (mL)
To convert to micrograms per syringe unit (a 1 mL insulin syringe has 100 units, so 1 unit = 0.01 mL):
mcg per unit = concentration (mg/mL) × 10 Units to draw = desired dose (mcg) ÷ mcg per unit
Worked example: A 10 mg vial reconstituted with 2 mL of BAC water = 5 mg/mL, which is 50 mcg per unit. For a 250 mcg research dose, you'd draw 250 ÷ 50 = 5 units.
If you'd rather not do this by hand — or you're working with a blend (e.g. a BPC-157 + TB-500 stack), where each component has its own concentration — the Peptide Reconstitution Calculator does it for you and shows the exact fill on a syringe diagram.
How much BAC water to add (mg-by-mg chart)#
There's no single "correct" volume — you choose it to land on an easy-to-draw concentration. More water = a lower concentration and a larger, easier-to-measure draw; less water = a higher concentration and a smaller draw. This chart shows common vial sizes and the concentration each water volume produces:
| Vial size | BAC water | Concentration | Per syringe unit | 250 mcg dose | 500 mcg dose |
|---|---|---|---|---|---|
| 5 mg | 1 mL | 5 mg/mL | 50 mcg | 5 units | 10 units |
| 5 mg | 2 mL | 2.5 mg/mL | 25 mcg | 10 units | 20 units |
| 10 mg | 1 mL | 10 mg/mL | 100 mcg | 2.5 units | 5 units |
| 10 mg | 2 mL | 5 mg/mL | 50 mcg | 5 units | 10 units |
| 10 mg | 3 mL | 3.33 mg/mL | 33 mcg | 7.5 units | 15 units |
| 15 mg | 3 mL | 5 mg/mL | 50 mcg | 5 units | 10 units |
| 20 mg | 2 mL | 10 mg/mL | 100 mcg | 2.5 units | 5 units |
| 30 mg | 3 mL | 10 mg/mL | 100 mcg | 2.5 units | 5 units |
A common shortcut is the "add a zero" method: add BAC water in units equal to 10× the mg in the vial (e.g. 10 mg → 100 units → 1 mL), which always lands you at 10 mg/mL. It's a handy default, but a slightly larger water volume gives you a more precise draw for small doses.
Standard vials hold about 3 mL (300 units) at most — don't try to add more water than the vial can physically hold.
Storage and shelf life after reconstitution#
- Reconstituted with BAC water: refrigerate at 2–8 °C; typically stable for several weeks (often cited as ~4–6 weeks, compound-dependent). The benzyl alcohol is what buys you that window.
- Reconstituted with plain sterile water: no preservative — use within roughly 24 hours.
- Don't freeze a reconstituted vial unless the specific compound's data supports it; freeze-thaw cycles can degrade peptides.
- Keep it dark. Light and heat accelerate degradation. (protein drug stability)
Common mistakes to avoid#
- Shaking the vial. The single most common error. Swirl, don't shake.
- Spraying water onto the powder cake. Aim down the wall.
- Using plain tap or "distilled" water. Only sterile/bacteriostatic water for injection.
- Skipping the alcohol swab. Both stoppers, every time.
- Guessing the concentration. A wrong water volume means every dose afterward is wrong. Use the chart or the calculator.
- Using cloudy solution. Clear only.
Frequently asked questions
How much BAC water do I use to reconstitute peptides?
Enough to reach an easy-to-draw concentration — there's no fixed amount. For a 10 mg vial, 1–3 mL is typical (giving 10, 5, or 3.33 mg/mL respectively). Use the chart above or the reconstitution calculator to match a water volume to your target dose.
How do you reconstitute a 5 mg peptide?
Add 1 mL of BAC water for a 5 mg/mL solution (50 mcg per syringe unit), or 2 mL for 2.5 mg/mL (25 mcg per unit) if you want a larger, easier draw. Swirl gently until clear.
How do you reconstitute 30 mg of peptides?
Add about 3 mL of BAC water for a 10 mg/mL solution (100 mcg per unit). Note that 3 mL is roughly the capacity of a standard vial, so 30 mg vials are usually mixed at a higher concentration.
Can I use regular water or saline instead of BAC water?
No. Use bacteriostatic water (multi-dose) or sterile water for injection (single use). Tap, distilled, or drinking water is not sterile and is not appropriate for injection.
Do I shake the vial to mix the peptide?
Never shake. Swirl or gently roll the vial. Shaking creates shear stress and foam that can denature the peptide.
How long does a reconstituted peptide last?
With BAC water, typically several weeks refrigerated (often ~4–6 weeks, compound-dependent). With plain sterile water, about 24 hours.
Where to buy peptides and supplies#
Reconstitution starts with a quality vial and a proper COA. We track live prices across vetted vendors — Peptide Supply Co. is our top-rated source. Compare current pricing on popular compounds:
For compound-specific buying guides, see where to buy BPC-157, where to buy tirzepatide, and where to buy retatrutide.
Sources
- Bacteriostatic Water for Injection, USP — DailyMed label
- Frokjaer S, Otzen DE. Protein drug stability: a formulation challenge. Nat Rev Drug Discov, 2005
- Formulation composition and process effects on a lyophilized peptide (CSP7) — PMC
- Gershanik J, et al. The gasping syndrome and benzyl alcohol poisoning — PubMed