Peptide Storage and Reconstitution: The Complete Guide

Written by Adam Maggio | Medically reviewed by Dr. Sarah Chen, PharmD, BCPS

Lyophilized (freeze-dried) peptides are stable at room temperature for months but should be refrigerated for long-term storage. Reconstitute with bacteriostatic water (not sterile water) for multi-dose vials. Once reconstituted, store at 2–8°C and use within 30 days. Never freeze reconstituted peptides.

Understanding Lyophilized Peptides

Most research peptides are supplied in lyophilized (freeze-dried) form — a white powder in a sealed glass vial. Lyophilization removes water from the peptide solution, dramatically extending shelf life and stability. Lyophilized peptides are stable at room temperature for 6–12 months and at refrigerator temperature (2–8°C) for 1–2 years or longer. Freezing lyophilized peptides is acceptable for very long-term storage.

Reconstitution: Step-by-Step

1. Gather supplies: bacteriostatic water (BW), alcohol swabs, insulin syringe, and the peptide vial. 2. Wipe the tops of both vials with alcohol swabs. 3. Draw the desired volume of bacteriostatic water into the syringe. 4. Inject the BW slowly down the side of the peptide vial — do not inject directly onto the powder. 5. Gently swirl (do not shake) until the powder is fully dissolved. 6. The solution should be clear and colorless. 7. Label the vial with the date of reconstitution and the concentration.

Calculating Concentration

If you add 1 mL of BW to a 5 mg vial, the concentration is 5 mg/mL = 5000 mcg/mL. For a 500 mcg dose, draw 0.1 mL (10 units on an insulin syringe). If you add 2 mL of BW to the same vial, the concentration is 2.5 mg/mL = 2500 mcg/mL. For a 500 mcg dose, draw 0.2 mL (20 units). Use more BW for easier dose measurement; use less for smaller injection volumes.

Why Bacteriostatic Water?

Bacteriostatic water contains 0.9% benzyl alcohol, which inhibits bacterial growth and allows the vial to be used multiple times over 28–30 days. Sterile water (without benzyl alcohol) should only be used for single-dose vials, as it does not prevent bacterial contamination after the first use. Never use tap water, distilled water, or saline for peptide reconstitution.

Storage After Reconstitution

Store reconstituted peptides at 2–8°C (refrigerator temperature). Use within 28–30 days. Do not freeze reconstituted peptides — freezing can cause aggregation and loss of potency. Keep away from light. If the solution becomes cloudy, develops particles, or changes color, discard it.

Signs of Degraded Peptides

Discard peptides if: the lyophilized powder has turned yellow or brown; the reconstituted solution is cloudy or has visible particles; the vial seal was compromised; the peptide was stored improperly (e.g., left at room temperature for weeks after reconstitution). When in doubt, discard and use a fresh vial.