# How to reconstitute a peptide or GLP-1 vial (step by step)

> What reconstitution means, why lyophilized peptides need bacteriostatic water, and the math that turns a vial of powder into an exact, drawable dose.

Source: https://glp-1-app.com/learn/how-reconstitution-works/

Education · not medical advice

## How reconstitution works

Many compounded and research peptides ship as a freeze-dried powder. Before use they're “reconstituted” — dissolved in liquid. Here's the why and the math.

### Why powder, and why water

Peptides are more stable stored dry (lyophilized). To use one, you add a sterile liquid — usually **bacteriostatic water** (water with a tiny amount of benzyl alcohol that inhibits bacterial growth, so a vial can be used over multiple days). The powder dissolves into a known concentration you can then draw from.

### The three numbers that matter

1. **Vial strength** — mg of powder in the vial (on the label).
2. **Bacteriostatic water** — mL you add. You choose this.
3. **Target dose** — mg you want to draw each time.

From those, everything else follows:

concentration = vial mg ÷ water mL volume per dose = dose mg ÷ concentration units (U-100) = volume mL × 100

### Choosing how much water to add

There's no single correct volume — it's a trade-off. More water makes a _dilute_ solution: larger, easier-to-read draws but fewer mg per mL. Less water makes a _concentrated_ solution: tiny draws that are harder to measure precisely. A good calculator lets you try a volume and immediately see the resulting units and doses-per-vial, so you can pick a comfortable draw.

### Handling & storage

Reconstituted vials are typically refrigerated and have a limited beyond-use window (often cited around 28 days, but follow your pharmacy's label). Track the reconstitution date so you don't use a vial past its window.

### Keep reading

### Sources

This tool converts the numbers you enter — it never recommends a dose. Its constants are cited below; the warnings are arithmetic checks, not clinical limits.

- Syringe "units" are a volume marking, not a drug amount: a U-100 syringe reads 100 units = 1 mL (U-40 = 40 units/mL). The calculator converts mg ↔ mL ↔ units on this standard — it never assumes units equal mg.[Standard insulin concentration, U-100 = 100 units/mL (PMC5505430) ↗](https://pmc.ncbi.nlm.nih.gov/articles/PMC5505430/)
- The volume to draw is (drug ordered ÷ drug available) × the vial's total mL — i.e. dose ÷ concentration, where concentration (mg/mL) = vial mg ÷ bacteriostatic water mL. You enter every number; the tool only does this arithmetic.[Dose-volume formula — StatPearls "Dose Calculation" (Bookshelf NBK430836) ↗](https://www.ncbi.nlm.nih.gov/books/NBK430836/)
- An opened (punctured) multi-dose vial is dated and discarded within 28 days unless the manufacturer states otherwise.[CDC Injection Safety (per USP General Chapter ) ↗](https://www.cdc.gov/injection-safety/hcp/clinical-safety/index.html)

Educational only — not medical advice and not a recommended dose. Some peptides are not approved for human use. Confirm everything with a licensed clinician.

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