Most compounded GLP-1 vials ship as a ready-to-inject liquid solution. A minority ship as lyophilized powder — freeze-dried drug that the patient reconstitutes with bacteriostatic water at home before first use. Reconstitution is safe and well-documented when done correctly, but it adds several technical steps that the regular liquid format doesn't require, and the math for the resulting concentration is a consistent source of patient confusion. This guide walks through the process step by step with the FDA-adjacent safety boundaries and the concentration math that flows into our unit converter tool. Note: this is an educational explainer, not a substitute for the instructions that ship with your specific vial.

Before you start — the safety boundaries

Reconstitution is a sterile procedure. The boundaries that protect you from contamination and dose error come from the USP General Chapter <797> framework that governs compounded sterile preparations [1] and the FDA compounding guidance for patients [2]:

Follow the instructions that ship with your specific vial, not a generic recipe. Every compounding pharmacy has a specific protocol for the product they dispense, including the exact volume of bacteriostatic water to add, the target concentration, and the post-reconstitution BUD (beyond-use date). If your vial shipped without instructions, call the pharmacy before opening it.
Use bacteriostatic water, not sterile water or saline. Bacteriostatic water for injection (BWFI) contains 0.9% benzyl alcohol as a bacteriostatic preservative, which prevents microbial growth in a multi-dose vial across its BUD [5]. Plain sterile water for injection (SWFI) does not contain a preservative and is only appropriate for single-use preparations — reconstituting a multi-dose GLP-1 vial with SWFI would shorten the BUD dramatically. Saline is isotonic but also not appropriate for peptide reconstitution unless your pharmacy specifically dispensed it.
Single-use syringe and needle for drawing the water, separate from the one you use for injecting the dose. Cross-contamination between reconstitution and injection steps is a known infection source.
Clean, flat, dry surface away from airflow, pets, and children. The reconstitution process takes 2-3 minutes but any contamination at this stage affects every subsequent dose from that vial.
Once reconstituted, refrigerate and respect the BUD the pharmacy assigned on the label. Typical BUDs for reconstituted compounded GLP-1s refrigerated are 28-90 days depending on the pharmacy's stability documentation [1].

Step-by-step reconstitution

The generic reconstitution sequence for a lyophilized compounded GLP-1 vial:

Wash hands thoroughly with soap and water, then dry. Set out your supplies on a clean flat surface: lyophilized vial, bacteriostatic water vial, reconstitution syringe (usually 3-5 mL), alcohol pads, sharps container.
Inspect both vials. The drug vial should contain a dry powder cake, white or off-white, with no visible discoloration. The bacteriostatic water vial should be clear with no particulates. If either vial looks abnormal, do not use it — call the pharmacy.
Wipe both vial stoppers with a fresh alcohol pad and let the alcohol air-dry fully (10-15 seconds). Do not blow on it.
Draw the bacteriostatic water. Use the reconstitution syringe to draw the exact volume specified by your pharmacy (commonly 2 mL, 3 mL, or 5 mL depending on the target concentration). Point the needle up and tap the syringe to dislodge any air bubbles, then press the plunger gently to expel them.
Inject the water into the drug vial slowly. Insert the needle into the drug vial stopper at a 45-degree angle (this reduces coring) and slowly press the plunger so the water streams gently against the vial wall, not directly onto the lyophilized powder cake. Streaming water directly into the cake can denature the peptide.
Withdraw the syringe and dispose of it in a sharps container. Do not recap the needle.
Dissolve the powder by gentle rotation. Hold the vial between your hands and roll it gently in a circular motion for 30-60 seconds. Do not shake. Shaking foams the peptide solution and can denature the drug. The powder should fully dissolve within about a minute; if it doesn't, continue gentle rotation for another minute or two.
Inspect the reconstituted solution. It should be clear or very lightly opalescent with no visible particles. If it's cloudy or has visible particles, do not use it — call the pharmacy.
Label the vial with the reconstitution date and the BUD assigned by the pharmacy. This is the one label you should never skip — patients frequently forget when they reconstituted a vial and then use it past BUD.
Refrigerate at 2-8°C (36-46°F) between doses, unless the pharmacy specifically says otherwise.

The concentration math

The resulting concentration (mg/mL) depends on the amount of drug in the vial and the volume of bacteriostatic water you add. The formula:

concentration (mg/mL) = drug mg in vial ÷ water volume mL

Common compounded vial + reconstitution combinations:

Drug mg in vial	+ BWFI volume	= Concentration
5 mg semaglutide	2 mL	2.5 mg/mL
10 mg semaglutide	2 mL	5 mg/mL
10 mg semaglutide	4 mL	2.5 mg/mL
20 mg tirzepatide	2 mL	10 mg/mL
30 mg tirzepatide	3 mL	10 mg/mL
40 mg tirzepatide	4 mL	10 mg/mL

Once you know the concentration, you can compute the syringe units for any desired dose using our GLP-1 unit converter. The most important point: the concentration depends entirely on how much water you added, so if you add a different volume than the pharmacy specified, your unit-to- mg math changes and every subsequent dose will be wrong. Always follow the pharmacy's reconstitution instructions exactly.

Common reconstitution errors

Shaking instead of rolling. Shaking foams the solution, denatures the peptide, and can reduce potency significantly. Gentle rotation only.
Using the wrong water. Bacteriostatic water has the preservative needed for multi-dose storage. Sterile water for injection or saline does not. Your pharmacy should ship bacteriostatic water with the lyophilized vial — if they didn't, call them.
Adding the wrong volume. The math only works if the volume matches what the pharmacy specified. If your instructions say 2 mL and you added 3 mL, your concentration dropped by 33% and every dose you draw will be 33% too low. Discard and start over with a fresh vial.
Streaming water directly into the powder cake. The force of water jet on the lyophilized cake can denature the surface peptide. Aim the stream against the vial wall instead so the water gently dissolves the cake from the edges inward.
Not labeling the reconstitution date. Without a date on the vial you cannot track the BUD. The reconstitution date is the most important label in the entire process.
Freezing the reconstituted solution. Same rule as brand-name pens — never freeze a GLP-1 solution. Freezing denatures the peptide.

When reconstitution is the wrong format for you

Lyophilized vials are uncommon in the compounded GLP-1 market because most patients prefer the simplicity of a ready-to-inject liquid. If you're uncomfortable with the reconstitution process:

Ask your telehealth provider if they can switch you to a pharmacy that dispenses ready-to-inject liquid vials. Most can.
If you're on commercial insurance that covers Wegovy or Zepbound, the brand-name pens are pre-filled and require no reconstitution at all. The patient-experience difference is meaningful.
If cost is the reason you're on lyophilized powder in the first place, the new Foundayo (orforglipron) approval includes a $149/month self-pay tier that may be price-competitive. See our Foundayo approval deep-dive.

Safety disclaimer

This guide is educational and does not replace the written instructions that ship with your vial or the clinical judgment of your prescriber. If you are unsure about any step of the reconstitution process, call your compounding pharmacy before opening the vial. Do not use any vial that looks abnormal, is past its BUD, or wasn't reconstituted correctly.

Related research and tools

For the concentration-to-units math that flows from any reconstitution, use our GLP-1 unit converter. For the injection technique after the vial is reconstituted, see our injection guide. For post-reconstitution storage rules and BUD, see our storage guide. For the 503A/503B distinction that governs how compounding pharmacies can operate, see our PCAB investigation. For what FDA has actually cited compounded GLP-1 pharmacies for, see our FDA warning letters database.

References

1.U.S. Pharmacopeial Convention. USP General Chapter <797> Pharmaceutical Compounding — Sterile Preparations. USP-NF. 2023. https://www.usp.org/compounding/general-chapter-797
2.U.S. Food and Drug Administration. Compounded Drug Products — 503A and 503B Outsourcing Facility Information for Patients. FDA Drug Compounding Resources. 2024. https://www.fda.gov/drugs/human-drug-compounding/compounding-and-fda-questions-and-answers
3.Novo Nordisk Inc. WEGOVY (semaglutide) injection — US Prescribing Information. FDA Approved Labeling. 2025. https://www.accessdata.fda.gov/drugsatfda_docs/label/2025/215256s024lbl.pdf
4.Eli Lilly and Company. ZEPBOUND (tirzepatide) injection — US Prescribing Information. FDA Approved Labeling. 2025. https://www.accessdata.fda.gov/drugsatfda_docs/label/2025/217806s016lbl.pdf
5.U.S. Food and Drug Administration. Bacteriostatic Water for Injection — Labeling and Patient Information. FDA Drug Label Resources. 2024. https://www.accessdata.fda.gov/scripts/cder/daf/