1. Make a clean space
Wash and dry your hands. Clear a clean, dry work area away from sinks, food, pets and trash.
Start here · plain-language guide
Bacteriostatic water reconstitution, explained simply
Reconstitution means adding sterile liquid to dry powder so it becomes a liquid. Think of it like adding water to a drink mix — except everything must stay sterile, and every number must come from the pharmacy label or your clinician.
This page teaches the process and the maths. It does not choose a dose.
Only mix a medicine that was prescribed and dispensed for you. Use the exact diluent, amount, storage rule and discard date on its label. Ask a pharmacist before starting if any direction is missing or unclear.
What to put on the clean table
- Your labeled powder vial
- The exact diluent named on the label
- A new sterile syringe and needle for mixing
- A new U-100 syringe only if your directions use one
- At least two fresh alcohol swabs
- A label and pen
- An FDA-cleared sharps container
Seven small steps
2. Check every label
Read the peptide vial, bacteriostatic-water vial and pharmacy directions. Stop if a seal is broken, a vial is cracked or the instructions do not agree.
3. Clean both rubber tops
Use a new alcohol swab on each rubber stopper. Let both tops air-dry completely. Do not blow on them or touch them afterward.
4. Move the prescribed water
With a new sterile needle and syringe, draw only the amount of water written in your directions. Push it slowly against the inside wall of the powder vial.
5. Be gentle
Let the water run down the glass. Gently roll or swirl only if the product directions allow it. Do not shake hard.
6. Label it now
Write the date mixed, total milligrams, water added, concentration and discard date. Never depend on memory.
7. Store it exactly as directed
Follow the pharmacy or manufacturer label. Many mixed products are refrigerated at 36–46°F (2–8°C), but that is not a rule for every product.
One common maths example
10 mg powder + 2 mL water
10 mg
amount in the vial
÷ 2 mL
water added
= 5 mg/mL
final concentration
That result describes how strong the liquid is. It does not tell anyone how much to inject. A prescribed dose is a separate number.
Same rule, different vial sizes
The rule never changes: milligrams in vial ÷ millilitres added = milligrams per millilitre.
| Powder vial | Water added | Concentration |
|---|---|---|
| 5 mg vial | 1 mL water | 5 mg/mL |
| 5 mg vial | 2 mL water | 2.5 mg/mL |
| 10 mg vial | 1 mL water | 10 mg/mL |
| 10 mg vial | 2 mL water | 5 mg/mL |
| 20 mg vial | 2 mL water | 10 mg/mL |
What “100 units” means
A U-100 insulin syringe is a tiny ruler for liquid. On that ruler, 100 units = 1 mL. It does not mean the syringe contains 100 doses.
1 unit
0.01 mL
10 units
0.10 mL
50 units
0.50 mL
100 units
1.00 mL
- A 30-unit or 50-unit U-100 syringe uses the same scale; it simply holds less liquid.
- Use a new sterile syringe and needle every time. Never reuse or share either one.
- Do not touch the needle. If it touches anything, discard it safely and start with a new one.
- Put used needles straight into a sharps container. Never leave them loose or recap them by hand.
Alcohol swabs: use a fresh one every time
A plastic flip-cap keeps dust out; it does not make the rubber top sterile. Wipe the rubber stopper before the first puncture and before every later puncture, then let it dry. Use a separate fresh swab for the injection site if your clinician has taught you to inject. Never use one swab for everything.
When does a mixed vial expire?
- 1. First, read the pharmacy or manufacturer label. Its discard date and storage directions win.
- 2. Mark the vial. Write the date it was mixed or first punctured and the discard date.
- 3. Do not assume every vial lasts 28 days. The common 28-day rule applies to many opened multidose vials only when the manufacturer does not give another date. A mixed medicine may have a shorter date.
- 4. Throw it away sooner when safety is uncertain. Do not use it after improper storage, a damaged stopper, suspected contamination, or an unexpected change in color, cloudiness or particles.
Bacteriostatic water and the mixed medicine are two different vials and may have different discard dates. Never copy the water vial's date onto the medicine vial unless the pharmacy explicitly says to.
Use your own labeled numbers
The calculator on this page checks concentration and converts a clinician-prescribed amount into volume. It never chooses a dose.
Printable guide
Take the simple steps with you
Download the full guide with the clean-setup checklist, seven steps, concentration examples, U-100 markings, expiration guidance and safety sources.
Beginner maths tools
Reconstitution & syringe calculator
These three calculators handle concentration, water-for-target strength and draw-volume arithmetic. They convert numbers only: your dose always comes from your prescriber, never from this page.
Lyophilised powder
The freeze-dried peptide puck in the vial. It is inactive until liquid is added.
Bacteriostatic water (BAC)
Sterile water with 0.9% benzyl alcohol, which slows bacterial growth so a multi-dose vial can be stored in the fridge.
Concentration (mg/mL)
How many milligrams of peptide are in each millilitre of liquid after mixing. More water = weaker liquid; less water = stronger.
U-100 insulin syringe
A 1 mL syringe marked in 100 'units'. So 10 units = 0.1 mL and 25 units = 0.25 mL, always.
Calculator 1 — What is my concentration?
Enter the peptide amount printed on the vial and how much bacteriostatic water you added. The calculator shows the strength of the liquid you now have.
Printed on the vial label, e.g. 5 mg, 10 mg, 30 mg.
Total liquid you injected into the vial.
Concentration
5 mg/mL
10 mg ÷ 2 mL
Per 0.1 mL (10 units)
0.5 mg
Each small block of 10 units on the syringe
Per 1 unit
50 mcg
One single unit line on a U-100 syringe
Calculator 2 — How much water should I add?
Working backwards: pick the strength you want the liquid to be, and the calculator tells you how much bacteriostatic water to add to the vial. Beginners usually find a round number (like 5 mg/mL) easier to measure with.
Example: 5 means every 1 mL of liquid contains 5 mg.
Add this much water
2 mL
10 mg ÷ 5 mg/mL
Same in syringe units
200 units
Drawn into a U-100 syringe to add to the vial
Calculator 3 — How far do I draw the syringe?
Enter the dose your prescriber gave you (in mg). Using the concentration from Calculator 1, this shows the volume to draw. This tool converts numbers only — it never tells you what dose to take.
Only ever the dose given to you by your clinician.
5 mg/mL
From Calculator 1 above.
Enter your prescribed dose above (and complete Calculator 1) to see the draw amount.
Read this before mixing anything
Wrong maths can cause a serious overdose. Double-check every number, and if anything is unclear, ask a pharmacist or your prescriber before injecting.
- Never inject a peptide that was not prescribed or dispensed for you. Compounded and grey-market vials are not FDA-approved and may be mislabelled or contaminated.
- Wash hands, swab the vial top with alcohol, use a brand-new sterile syringe every time, and never share vials or needles.
- Add water slowly down the inside wall of the vial and gently swirl — never shake the vial hard.
- Store the mixed vial in the fridge, label it with the date and concentration, and discard it if the liquid turns cloudy or particles appear.
- Retatrutide is investigational and not approved anywhere; any non-trial supply is unregulated with no quality guarantee.
Beginner tip: write the vial maths on a sticky label on the vial itself — “10 mg in 2 mL = 5 mg/mL, 10 units = 0.5 mg”. Doing the maths once, correctly, and labelling it prevents repeat mistakes far better than recalculating from memory each week.