What does “reconstitution” mean?
Compounded semaglutide is often dispensed as a lyophilized powder — the same technology used to stabilize many injectable medications for long-term storage and shipping. Lyophilization (freeze-drying) removes moisture from the peptide, making it stable at room temperature for a longer period than a pre-mixed liquid.
Before injection, the powder must be dissolved in a diluent — almost always bacteriostatic water — to create a liquid solution. That process is called reconstitution.
Note: some compounding pharmacies dispense semaglutide as a pre-mixed liquid solution, which does not require reconstitution. If your pharmacy provides a pre-filled vial with a liquid already inside, skip to the storage and dosing sections below. Your pharmacy label and prescription paperwork will clarify which format you received.
Why bacteriostatic water, not regular sterile water?
Bacteriostatic water for injection contains 0.9% benzyl alcohol, a preservative that inhibits microbial growth. Because you will draw from the same vial multiple times over several weeks, the preservative is essential to prevent bacterial contamination between uses.
Sterile water for injection (SWFI) lacks a preservative and is safe only for single-use preparations. Using SWFI in a multi-dose vial of compounded semaglutide creates infection risk. Bacteriostatic water is available at most pharmacies without a prescription, though it may be sourced through your compounding pharmacy as part of your kit.
Volume to inject equals your prescribed dose in milligrams divided by the concentration in milligrams per milliliter — everything else is detail.
How do you calculate the correct semaglutide dose to inject?
The math behind a semaglutide reconstitution calculator is straightforward. Two equations cover everything you need:
Step 1: calculate your solution concentration
Concentration (mg/mL) = total semaglutide (mg) ÷ volume of bacteriostatic water added (mL)
| Vial size | Bacteriostatic water added | Resulting concentration |
|---|---|---|
| 5 mg | 2 mL | 2.5 mg/mL |
| 5 mg | 1 mL | 5 mg/mL |
| 10 mg | 2 mL | 5 mg/mL |
Your compounding pharmacy specifies the correct bacteriostatic water volume for your vial. Do not change this volume without confirming with your clinician or pharmacist — it changes every dose calculation downstream.
Step 2: calculate the volume to inject
Volume to inject (mL) = prescribed dose (mg) ÷ concentration (mg/mL)
| Prescribed dose | At 2.5 mg/mL | At 5 mg/mL |
|---|---|---|
| 0.25 mg | 0.1 mL | 0.05 mL |
| 0.5 mg | 0.2 mL | 0.1 mL |
| 1.0 mg | 0.4 mL | 0.2 mL |
| 1.7 mg | 0.68 mL | 0.34 mL |
| 2.4 mg | 0.96 mL | 0.48 mL |
Use an insulin syringe marked in 0.01 mL increments for accuracy at small volumes. U-100 insulin syringes (1 mL total) are the standard tool; 29–31 gauge needles minimize injection discomfort.
How do you reconstitute semaglutide powder step by step?
- Wash hands thoroughly with soap and water for at least 20 seconds before handling any injectable medication.
- Gather supplies: semaglutide vial, bacteriostatic water vial, drawing syringe (1–3 mL), needle for drawing, alcohol swabs.
- Swab both vial tops with alcohol swabs and allow to air-dry for 15–30 seconds.
- Draw the bacteriostatic water into your syringe (the volume specified by your pharmacy — typically 1–2 mL).
- Inject the water slowly into the semaglutide vial, directing the stream toward the glass wall rather than directly onto the powder to avoid foaming. Do not shake.
- Gently roll the vial between your palms in a circular motion until the powder is fully dissolved. The solution should be clear and colorless. If it is cloudy or has visible particles, do not use it.
- Label the vial with the date of reconstitution and the beyond-use date provided by your pharmacy.
- Refrigerate immediately — do not leave reconstituted semaglutide at room temperature for extended periods.
How should you store semaglutide after reconstitution?
Store reconstituted semaglutide in the refrigerator between 36–46°F (2–8°C). Do not freeze the vial. Freezing can denature the peptide and render it ineffective. Most compounded semaglutide vials have a beyond-use date of 28 to 56 days after reconstitution, depending on the specific formulation and pharmacy — always follow the label.
Protect the vial from direct light. Some peptides degrade when exposed to UV light; keeping the vial in its original box or a dark storage area is a simple precaution.
If you need to travel, an insulated cooler or travel medication case can keep the vial in the safe temperature range. Semaglutide can typically tolerate brief room-temperature exposure (under 77°F) for up to 28 days according to reference data for branded semaglutide — but always check with your pharmacy for compounded product-specific guidance.
When should you ask your clinician or pharmacist?
This guide covers general reconstitution principles. Your specific vial, dose, and protocol may differ. Always defer to your compounding pharmacy’s written instructions and your prescribing clinician for anything vial-specific. Contact them if:
- Your solution appears cloudy, discolored, or has visible particles
- You are unsure about the concentration your pharmacy used
- Your dose has changed and you need to recalculate the injection volume
- You accidentally used sterile water instead of bacteriostatic water
- Your vial was left unrefrigerated for an extended period
You can learn more about how clinician-supervised semaglutide programs work at PepScribe on the semaglutide program page. All compounded medication is prepared in the USA by licensed 503A pharmacies — no hidden overseas supply chain.
Frequently asked questions
What is semaglutide reconstitution?
Reconstitution is the process of dissolving compounded semaglutide lyophilized (freeze-dried) powder in bacteriostatic water to create an injectable solution. Your pharmacy will typically provide reconstitution instructions and the correct volume of bacteriostatic water for the specific vial you receive.
How much bacteriostatic water do I use to reconstitute semaglutide?
The volume depends on the milligrams of semaglutide in your vial and the concentration your clinician prescribed. A common example: a 5 mg vial reconstituted with 2 mL of bacteriostatic water yields a 2.5 mg/mL solution. Always follow the specific instructions that come with your compounded vial — concentrations vary by pharmacy and prescription.
Can I use regular sterile water instead of bacteriostatic water?
No. Bacteriostatic water contains benzyl alcohol, a preservative that prevents bacterial growth in the vial after it has been opened and used multiple times. Sterile water for injection does not contain a preservative and is only safe for single-use applications. Compounded semaglutide vials are multi-dose and require bacteriostatic water.
How do I know what dose to draw after reconstitution?
Your clinician or pharmacist will specify both your dose in milligrams and the volume to draw in milliliters based on the concentration of your reconstituted vial. Use the formula: volume (mL) = dose (mg) ÷ concentration (mg/mL). For a 0.25 mg dose from a 2.5 mg/mL solution: 0.25 ÷ 2.5 = 0.1 mL.
How should reconstituted semaglutide be stored?
Store reconstituted semaglutide in the refrigerator at 36–46°F (2–8°C). Do not freeze. Most compounded semaglutide vials are stable for 28–56 days after reconstitution when refrigerated — check the expiry or beyond-use date on your pharmacy label. Protect from light.