How to Reconstitute Peptides
Step-by-step guide with dose calculations
Peptides are shipped as a freeze-dried (lyophilized) powder. Before you can inject or dose a peptide, you need to reconstitute it — that simply means adding sterile water to turn the powder into an injectable solution. This guide walks you through every step: what supplies you need, how to mix safely, how to calculate your exact dose in syringe units, and how to store your reconstituted vial.
What Is Reconstitution and Why Is It Needed?
Peptides are manufactured and shipped as a lyophilized (freeze-dried) powder because the dry form is far more stable than a liquid. Reconstitution is the process of adding a precise amount of sterile water to this powder to create an injectable solution.
You control the concentration by choosing how much water to add. Less water means a more concentrated solution (smaller injection volumes). More water means a more dilute solution (easier to measure small doses but larger injection volumes). The total amount of peptide in the vial stays the same regardless of how much water you add.
Why bacteriostatic water?
Bacteriostatic water (BAC water) contains 0.9% benzyl alcohol, which prevents bacterial growth. This is critical because you will draw from the vial multiple times over several weeks. Plain sterile water lacks this preservative and should only be used for single-use reconstitutions.
What You Need
Gather all supplies before you start. Everything should be sterile and sealed.
Bacteriostatic water (BAC water)
Usually sold in 30 mL vials. This is your mixing water. Do not substitute tap water, saline, or plain sterile water for multi-use vials.
Your peptide vial
Lyophilized powder with a rubber stopper and flip-off cap. Check the label for the total peptide content in milligrams (e.g. 5 mg).
Insulin syringes
Used both for drawing BAC water and for injecting your dose. Available in three common sizes — see the syringe guide below.
Alcohol swabs
70% isopropyl alcohol wipes for sterilizing vial stoppers before each needle insertion.
Insulin Syringe Sizes
All three sizes use the same needle gauge (typically 29–31G). The difference is total capacity and the graduation markings on the barrel.
0.3 mL / 30 units
Small doses (under 30 units)
Each tick mark = 0.5 units. The most accurate syringe for small peptide doses. Ideal for BPC-157, TB-500, and other peptides where your injection volume is small.
0.5 mL / 50 units
Medium doses (15–50 units)
Each tick mark = 1 unit. Good balance of accuracy and capacity. The most popular all-around choice for peptide users.
1.0 mL / 100 units
Larger doses (30–100 units)
Each tick mark = 2 units. Best for GLP-1 peptides (semaglutide, tirzepatide) or any dose requiring more than 50 units of solution.
Choosing the right syringe
The general rule: use the smallest syringe that can hold your dose. A smaller syringe has finer graduation marks, which means more accurate measurement. If your calculated dose is 8 units, a 0.3 mL syringe lets you measure that precisely. A 1.0 mL syringe would make 8 units very difficult to read accurately.
Step-by-Step Reconstitution Instructions
Follow these steps carefully. The entire process takes about 2 minutes once you have done it a few times.
Remove the flip-off caps
Pop off the colored plastic caps from both the peptide vial and the BAC water vial. This exposes the rubber stoppers underneath. Do not remove the rubber stoppers — the needle goes through them.
Swab the stoppers
Wipe the top of both rubber stoppers with a fresh alcohol swab. Let the alcohol air-dry for a few seconds. This is your primary contamination prevention step — never skip it.
Draw your BAC water
Insert the syringe needle into the BAC water vial. Turn the vial upside down. Pull back the plunger to draw your desired amount of BAC water (e.g. 1 mL or 2 mL). Remove any air bubbles by tapping the syringe and pushing the plunger slightly.
Inject water into the peptide vial
Insert the needle into the peptide vial at an angle, aiming the needle tip at the glass wall — not directly at the powder cake. Slowly depress the plunger so the water trickles down the inside wall of the vial. This prevents damaging the peptide with direct force.
Swirl gently — never shake
Once all the water is in, gently roll or swirl the vial between your fingers. The powder should dissolve within 30–60 seconds, producing a clear solution. If small particles remain, let the vial sit in the refrigerator for a few minutes and swirl again. Never shake the vial — vigorous agitation can denature (damage) the peptide.
Verify and store
The reconstituted solution should be clear and free of particles. If it appears cloudy or has visible clumps after several minutes, the peptide may have been damaged or contaminated. Label the vial with the date of reconstitution, then place it in the refrigerator immediately.
How to Calculate Your Dose
Once your peptide is reconstituted, you need to calculate how many units to draw in your syringe for each injection. This is simple math with three steps.
Find your concentration
Peptide amount (mcg) ÷ BAC water added (mL) = Concentration (mcg/mL)
Example: 5,000 mcg ÷ 2 mL = 2,500 mcg/mL
Calculate your injection volume
Desired dose (mcg) ÷ Concentration (mcg/mL) = Injection volume (mL)
Example: 250 mcg ÷ 2,500 mcg/mL = 0.10 mL
Convert to syringe units
Injection volume (mL) × 100 = Units on a 100-unit syringe
Example: 0.10 mL × 100 = 10 units
The quick version
Peptide (mcg) ÷ Water (mL) = Concentration. Dose ÷ Concentration = mL to draw. mL × 100 = syringe units on a U-100 syringe. Or skip the math and use the calculator.
Common Reconstitution Examples
These are the most common peptide and water combinations you will encounter. All assume a 100-unit (1 mL) insulin syringe.
| Peptide | Vial Size | BAC Water | Concentration | Typical Dose | Syringe Units |
|---|---|---|---|---|---|
| BPC-157 | 5 mg | 2 mL | 2,500 mcg/mL | 250 mcg | 10 units |
| BPC-157 | 5 mg | 2 mL | 2,500 mcg/mL | 500 mcg | 20 units |
| TB-500 | 5 mg | 1 mL | 5,000 mcg/mL | 2,500 mcg | 50 units |
| TB-500 | 5 mg | 2 mL | 2,500 mcg/mL | 2,500 mcg | 100 units |
| Semaglutide | 3 mg | 1.5 mL | 2,000 mcg/mL | 250 mcg | 12.5 units |
| Semaglutide | 5 mg | 2 mL | 2,500 mcg/mL | 500 mcg | 20 units |
| CJC-1295 / Ipamorelin | 5 mg | 2.5 mL | 2,000 mcg/mL | 300 mcg | 15 units |
Syringe units assume a U-100 (1 mL / 100-unit) insulin syringe. For U-50 syringes, divide the listed units by 2. For U-30 syringes, divide by 3.33.
Storage Guidelines
Proper storage is essential to maintain peptide potency. A reconstituted peptide is far more fragile than the original freeze-dried powder.
Store reconstituted vials in the refrigerator immediately after mixing. A dedicated shelf or container prevents accidental jostling.
BAC water's benzyl alcohol provides antimicrobial protection, but potency gradually declines. Label each vial with the reconstitution date.
Freezing and thawing causes ice crystals that can denature the peptide. Unreconstituted (powder) vials can be frozen for long-term storage.
Keep vials away from sunlight and heat sources. The refrigerator door is not ideal due to temperature fluctuation — use an interior shelf.
Powder vs. reconstituted storage
Unreconstituted powder: Stable at room temperature for weeks. For long-term storage (months), freeze at -20°C. No special handling needed beyond keeping it sealed and dry.
Reconstituted solution: Must be refrigerated immediately. Use within 4–6 weeks. Never freeze. Always swab the stopper before each draw to prevent contamination.
Common Mistakes to Avoid
These are the most frequent errors that can waste your peptide or compromise sterility.
Shaking the vial
Vigorous shaking creates foam and can denature the peptide, reducing or destroying its effectiveness. Always swirl gently or roll between your palms.
Using too much water
Adding excessive BAC water results in a very dilute concentration. This means you need to inject a large volume for each dose, which is uncomfortable and can waste syringe draws. Use 1–2 mL for most peptides.
Spraying water directly onto the powder
Forcing water directly onto the lyophilized cake can damage the peptide. Always aim the needle at the glass wall and let water trickle down slowly.
Skipping alcohol swabs
Failing to sterilize the vial stopper before each needle insertion introduces bacteria. This can contaminate the entire vial, especially over multiple weeks of use.
Using the wrong syringe size
Using a 1.0 mL (100-unit) syringe for a 5-unit dose makes accurate measurement nearly impossible. Match your syringe size to your dose volume — smaller is more precise.
Storing at room temperature
Reconstituted peptides degrade rapidly at room temperature. Always refrigerate immediately after mixing and after each use.
Reusing or sharing syringes
Insulin syringes are single-use. Reusing dulls the needle (causing pain and tissue damage) and introduces contamination risk. Never share syringes.
Using plain sterile water for multi-use vials
Sterile water without the bacteriostatic preservative allows bacteria to grow after the first needle insertion. Always use BAC water unless you plan to use the entire vial in a single dose.
Frequently Asked Questions
Can I use sterile water instead of BAC water?
Only if you plan to use the entire vial in a single dose. Sterile water has no preservative, so bacteria can grow after the first needle puncture. For multi-dose vials (the vast majority of use cases), always use bacteriostatic water.
How much BAC water should I add?
Typically 1–2 mL for most peptides. Less water means a more concentrated solution (smaller injection volumes). More water means a more dilute solution (easier to measure tiny doses). Refer to the examples table above for common amounts.
My powder didn't dissolve completely. Is it ruined?
Not necessarily. Some peptides take longer to dissolve. Place the vial in the refrigerator for 10–15 minutes, then gently swirl again. If chunks persist after 30 minutes, the peptide may have been damaged during shipping or storage.
Can I reconstitute a vial and re-freeze it?
No. Freezing a reconstituted peptide causes ice crystals that can denature the protein. Only unreconstituted (powder) vials should be frozen for long-term storage.
What does it mean if the solution looks cloudy?
A properly reconstituted peptide should be clear and colorless. Cloudiness or floating particles may indicate contamination or degradation. Do not inject a cloudy solution — discard the vial.
How do I know if my syringe is U-100?
Almost all insulin syringes sold in the US are U-100, meaning 100 units = 1 mL. Check the packaging — it will say U-100. The markings on the syringe barrel will go up to 30, 50, or 100 depending on the syringe size.
Skip the math — use the calculator
Enter your peptide amount and water volume to get exact syringe units for any dose. Free, instant, no sign-up.