Peptide Storage, Reconstitution, and Handling

Peptides come as a dry white powder in a small sealed vial. Before you can use them, you need to mix them with a liquid — a process called reconstitution. And before and after reconstitution, how you store them makes a huge difference in whether they stay potent or degrade into useless fragments. This guide walks you through everything step by step.

Why Do Peptides Come as a Powder?

Peptides are fragile molecules. In liquid form, they slowly break down over time — especially at room temperature. To extend shelf life, manufacturers use a process called lyophilization (freeze-drying) to remove all the water from the peptide solution, leaving behind a stable dry powder that can be stored for months or even years without degrading.

Think of it like instant coffee. The manufacturer brews the coffee, then removes all the water to create a stable powder. You add water back when you're ready to use it. Peptides work the same way.

What Is Bacteriostatic Water?

Bacteriostatic water (BAC water) is sterile water that contains 0.9% benzyl alcohol — a preservative that prevents bacteria from growing in the vial. This is important because once you add liquid to the peptide powder, the vial is no longer completely sealed, and bacteria could potentially contaminate it over time.

Regular sterile water works too, but it has no preservative, so you'd need to use the entire vial in one sitting. BAC water lets you draw multiple doses from the same vial over several weeks. Always use BAC water unless your specific peptide requires otherwise.

How to Reconstitute a Peptide Vial

Reconstitution is simpler than it sounds. Here is the basic process.

• Wash your hands thoroughly.
• Wipe the top of both the peptide vial and the BAC water vial with an alcohol swab. Let them dry for 10 seconds.
• Draw the desired amount of BAC water into a syringe (typically 1-2 mL for most vials).
• Insert the needle into the peptide vial and slowly push the water down the side of the vial — do not squirt it directly onto the powder.
• Gently swirl the vial (do not shake) until the powder is fully dissolved. The solution should be clear.
• Label the vial with the date and store in the refrigerator.

How Much BAC Water Should You Add?

The amount of BAC water you add determines the concentration of your solution — and therefore how much you need to draw for each dose. Use our Reconstitution Calculator to get the exact numbers for your specific peptide and dose. As a general rule, adding 1 mL of BAC water to a 5 mg vial gives you a concentration of 5 mg/mL.

Most people use insulin syringes (U-100) for drawing doses. These syringes are marked in units from 0 to 100, where 100 units = 1 mL. So if your concentration is 5 mg/mL and you want a 0.5 mg dose, you'd draw 10 units.

Storage: Before Reconstitution

Lyophilized (dry powder) peptide vials should be stored in a cool, dark place — ideally in the refrigerator (2-8°C / 36-46°F). They can often be stored at room temperature for short periods during shipping, but long-term storage at room temperature degrades them faster.

For very long-term storage (6+ months), some peptides can be stored in the freezer (-20°C). However, repeated freeze-thaw cycles damage peptides, so only freeze a vial if you don't plan to use it for a long time.

Storage: After Reconstitution

Once you've added BAC water, the clock starts ticking. Reconstituted peptides should always be kept in the refrigerator (never at room temperature or in the freezer). Most reconstituted peptides remain potent for 4-8 weeks when refrigerated properly. Some, like Semaglutide and Retatrutide, can last up to 45-60 days.

Injection Site Hygiene

Always use a fresh, sterile needle for each injection. Never reuse needles — they become dull and can introduce bacteria. Wipe the injection site with an alcohol swab before injecting and let it dry. Rotate injection sites to avoid building up scar tissue in one area.