How do you reconstitute a peptide?

To reconstitute a peptide: (1) Clean both vial tops with alcohol swabs. (2) Draw bacteriostatic water into a mixing syringe. (3) Insert the needle into the peptide vial and slowly release the water down the inside glass wall — never spray directly on the powder. (4) Gently swirl (never shake) until dissolved. (5) Label and refrigerate. The peptide is now ready for dosing with an insulin syringe.

How much bacteriostatic water should I add to a peptide vial?

The amount of bacteriostatic water determines your concentration. For a 5mg vial: adding 1mL gives 5,000 mcg/mL, adding 2mL gives 2,500 mcg/mL. For a 10mg vial: adding 1mL gives 10,000 mcg/mL, adding 2mL gives 5,000 mcg/mL. Choose an amount that makes your desired dose easy to measure on an insulin syringe. Use the TheDoseGuide dosing calculator for exact numbers.

How do I calculate peptide dosing after reconstitution?

Step 1: Convert vial size to mcg (mg × 1,000). Step 2: Divide total mcg by mL of water added to get concentration (mcg/mL). Step 3: Divide your desired dose (mcg) by concentration to get mL needed. Step 4: Multiply mL by your syringe's total units (usually 100 for a 1mL syringe) to get units to draw. Example: 5mg vial + 2mL water = 2,500 mcg/mL. For a 250 mcg dose: 250 ÷ 2,500 = 0.1 mL = 10 units on a 100-unit syringe.

What size syringe should I use for peptides?

Insulin syringes are standard for subcutaneous peptide injection. Common sizes: 100-unit (1mL) for standard doses, 50-unit (0.5mL) for smaller doses with better precision, and 30-unit (0.3mL) for very small doses. A 29–31 gauge needle is typical. Smaller syringes provide more precise measurements, which is important for accurate peptide dosing.

How to Reconstitute Peptides: Complete Step-by-Step Guide

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What Is Peptide Reconstitution?

Most research peptides arrive as a lyophilized powder — a freeze-dried cake or powder inside a sealed glass vial. Before use, this powder must be dissolved in a liquid (reconstituted) to create an injectable solution. The liquid used is called bacteriostatic water (BAC water), which is sterile water containing 0.9% benzyl alcohol as a preservative.

The amount of water you add determines the concentration of the solution, which directly affects how much liquid you draw into your syringe for each dose. Getting this right is essential for accurate dosing.

This guide walks through the entire process step-by-step, including worked examples for common peptides like BPC-157, TB-500, and Semaglutide.

What You'll Need

Lyophilized peptide vial — Check the label for the total amount in milligrams (common sizes: 5mg, 10mg, 30mg)
Bacteriostatic water (BAC water) — Sterile water with 0.9% benzyl alcohol preservative
Mixing syringe — 1mL or 3mL syringe with needle for transferring water (18–22 gauge)
Insulin syringe — For dosing after reconstitution (29–31 gauge, 100-unit or 50-unit)
Alcohol swabs — For sterilizing vial tops before use

⚠ Important: Always use bacteriostatic water for multi-dose vials, not sterile water. Sterile water lacks the preservative, meaning bacterial contamination can occur after the first use. With BAC water, reconstituted peptides remain stable for 4–6 weeks refrigerated.

Step-by-Step Reconstitution Process

1 Clean the Vial Tops

Wipe the rubber stopper of both the peptide vial and the bacteriostatic water vial with separate alcohol swabs. Allow them to air dry for a few seconds. This prevents contamination.

2 Draw Bacteriostatic Water

Using your mixing syringe, draw your desired amount of bacteriostatic water. Common amounts are 1mL or 2mL. The amount you choose determines your concentration — see the calculation section below to decide the best volume for your peptide and dose.

3 Add Water to the Peptide Vial

Insert the mixing syringe needle through the rubber stopper of the peptide vial. Aim the stream of water at the inside glass wall of the vial — let it run slowly down the side. Do NOT spray directly onto the lyophilized powder. Direct pressure can damage the peptide structure and reduce potency.

4 Swirl Gently — Never Shake

Once the water is added, gently roll the vial between your fingers or tilt it in slow circular motions. Never shake the vial — shaking creates air bubbles and can denature the peptide. The powder should dissolve within 1–3 minutes into a clear, colorless solution. If still cloudy, continue gently swirling.

5 Label and Refrigerate

Label the vial with: peptide name, reconstitution date, concentration (mcg/mL), and volume of water added. Store in the refrigerator at 36–46°F (2–8°C). Reconstituted peptides are typically stable for 4–6 weeks.

Pro Tip: If you reconstitute with 2mL and your dose is small, each dose requires drawing a tiny amount of liquid — this is more precise but harder to read on larger syringes. If you reconstitute with 1mL, each dose requires a larger draw, which is easier to read but depletes the vial faster. Choose based on your syringe size and comfort level.

How to Calculate Your Dose

Once reconstituted, you need to calculate exactly how much liquid to draw into your insulin syringe for a given dose. Here's the formula:

The Four-Step Formula

Convert vial size to mcg: Vial mg × 1,000 = total mcg
Calculate concentration: Total mcg ÷ mL of water added = mcg per mL
Calculate mL per dose: Desired dose (mcg) ÷ concentration (mcg/mL) = mL to inject
Convert to syringe units: mL to inject × syringe units = units to draw

Worked Example: BPC-157

BPC-157 · 5mg vial · 2mL BAC water · 250 mcg dose

Step 1: 5 mg × 1,000 = 5,000 mcg total

Step 2: 5,000 mcg ÷ 2 mL = 2,500 mcg/mL

Step 3: 250 mcg ÷ 2,500 mcg/mL = 0.1 mL

Step 4: 0.1 mL × 100 units = 10 units on a 100-unit syringe

Worked Example: TB-500

TB-500 · 5mg vial · 1mL BAC water · 2.5 mg (2,500 mcg) dose

Step 1: 5 mg × 1,000 = 5,000 mcg total

Step 2: 5,000 mcg ÷ 1 mL = 5,000 mcg/mL

Step 3: 2,500 mcg ÷ 5,000 mcg/mL = 0.5 mL

Step 4: 0.5 mL × 100 units = 50 units on a 100-unit syringe

Worked Example: Semaglutide

Semaglutide · 3mg vial · 1.5mL BAC water · 250 mcg dose

Step 1: 3 mg × 1,000 = 3,000 mcg total

Step 2: 3,000 mcg ÷ 1.5 mL = 2,000 mcg/mL

Step 3: 250 mcg ÷ 2,000 mcg/mL = 0.125 mL

Step 4: 0.125 mL × 100 units = 12.5 units on a 100-unit syringe

Syringe Size Guide

Syringe Size	Total Volume	Total Units	Best For
100-unit	1.0 mL	100	Standard dosing; most common choice
50-unit	0.5 mL	50	Smaller doses; better precision
30-unit	0.3 mL	30	Very small doses; maximum precision

A 29–31 gauge needle is standard for subcutaneous peptide injections. Thinner gauges (31G) are more comfortable but draw liquid more slowly.

Storage Best Practices

Before Reconstitution (Powder)

Store in freezer or refrigerator
Keep away from light and moisture
Powder vials can remain stable for months to years when stored properly

After Reconstitution (Liquid Solution)

Refrigerate immediately at 36–46°F (2–8°C)
Do NOT freeze reconstituted peptides — freezing can damage the peptide structure
Keep away from direct sunlight and heat
Use within 4–6 weeks for best potency
Always clean the vial stopper with an alcohol swab before each use

⚠ Signs of degradation: If the solution becomes cloudy, changes color, or develops visible particles after being stored, it may be degraded. Discard and reconstitute a fresh vial.

Common Mistakes to Avoid

Spraying water directly on the powder — Always aim at the glass wall. Direct pressure can denature the peptide.
Shaking the vial — This creates air bubbles and damages peptide bonds. Always swirl gently.
Using sterile water instead of BAC water — Sterile water has no preservative; the vial will be contaminated after the first use.
Storing at room temperature — Reconstituted peptides must be refrigerated immediately and kept cold.
Freezing reconstituted vials — Freezing can destroy the peptide structure. Only freeze un-reconstituted powder.
Reusing syringes — Always use a fresh insulin syringe for each injection to prevent contamination and ensure needle sharpness.
Not labeling vials — Always label with peptide name, date, and concentration. Multiple reconstituted vials can look identical.

Frequently Asked Questions

How much bacteriostatic water should I add? ▼

It depends on your vial size and desired dose. For a 5mg vial: 1mL gives 5,000 mcg/mL, 2mL gives 2,500 mcg/mL. Choose an amount that makes your dose easy to measure on your syringe. Use the TheDoseGuide calculator for exact numbers.

How long do reconstituted peptides last? ▼

Reconstituted with bacteriostatic water and stored at 36–46°F (2–8°C), peptides are typically stable for 4–6 weeks. With sterile water (no preservative), use within 24–48 hours.

What's the difference between bacteriostatic water and sterile water? ▼

Bacteriostatic water contains 0.9% benzyl alcohol as a preservative, preventing bacterial growth and allowing multi-dose use for 4–6 weeks. Sterile water has no preservative and must be used within 24–48 hours. Always use BAC water for peptide vials.

Can I use regular water to reconstitute peptides? ▼

No. Only use bacteriostatic water or sterile water for injection. Tap water, bottled water, and distilled water contain impurities and microorganisms that will contaminate the vial and degrade the peptide.

What syringe should I use for peptides? ▼

Insulin syringes in 100-unit (1mL), 50-unit (0.5mL), or 30-unit (0.3mL) sizes with 29–31 gauge needles. Smaller syringes provide more precise measurements for small doses.

What if the solution is cloudy after mixing? ▼

Continue gently swirling the vial — some peptides take longer to dissolve. If it remains cloudy after 10+ minutes, the peptide may have been damaged by heat, shaking, or contamination. It's best to discard and start with a fresh vial.

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The Complete Guide to Peptide Reconstitution for Beginners