Before you start
Important: This guide explains handling, not dosing. Unapproved peptides have not been tested for use in humans – you are responsible for quality, sterility and amount yourself. Approved prefilled pens (e.g. Mounjaro, Wegovy) are not reconstituted. Check how much water to use and how many units correspond to your amount in the calculator.
- Step 1
Get your supplies ready
- Vial with powder (white cake or powder, no discolouration)
- Bacteriostatic water (sterile water with 0.9 % benzyl alcohol) – no tap or mineral water
- Sterile U-100 insulin syringes, 0.5 or 1 mL – a new one for every injection
- Alcohol swabs, label or pen, sharps bin
- Clean work surface; wash your hands thoroughly
Reconstituting the vial
- Step 2
Disinfect the stoppers
Pull off the plastic caps and wipe both rubber stoppers – powder vial and BAC water – with an alcohol swab. Let the alcohol dry completely, otherwise it gets into the solution when you puncture the stopper.
- Step 3
Draw up the BAC water
Draw as much air into the syringe as the amount of water you want to remove, and inject it into the upright water vial. Then turn the vial upside down and slowly draw up the planned amount of water. For 2 or 3 mL, draw up several times with a 1 mL syringe and read it precisely each time.
The amount itself is up to you – it only determines the concentration. More on this in the guide How much water to reconstitute?
- Step 4
Let the water run down the glass wall
Pierce the stopper of the powder vial, hold the vial at a slight angle and point the needle so that the water runs slowly down the inner wall. Don't spray it forcefully straight onto the powder – that can damage delicate peptides and cause foaming.
Many vials are under vacuum and draw the water in by themselves. If it goes too fast, hold the plunger back slightly.
- Step 5
Swirl gently, label, refrigerate
Swirl the vial gently or roll it between your palms, do not shake. Some powders dissolve immediately, others need a few minutes in the fridge. The finished solution must be clear – cloudy, flaky or discoloured means: do not use (see the quality guide).
Note down the contents, amount of water, concentration and date – the Tracker prints a label for this. Then store at 2–8 °C, protected from light.
Injecting with the U-100 insulin syringe
- Step 6
Read the scale correctly
On a U-100 syringe, 100 units equal 1 mL, so one line (1 unit) is 0.01 mL. On 1 mL syringes often only every second line is marked, on 0.3 and 0.5 mL syringes every unit. You read it at the front edge of the black rubber stopper, not at the end of the plunger.
How many units correspond to your amount depends on the concentration – the calculator works this out. Background in the guide Converting units.
- Step 7
Draw up the amount and remove air
Disinfect the stopper again and let it dry. Inject a little air into the vial, turn the vial upside down and draw up a little more than needed. Hold the syringe with the needle pointing up, tap gently, push out the air and bring the stopper exactly to the correct line.
- Step 8
Choose the injection site
Suitable sites are the subcutaneous fat on the belly (at least 5 cm away from the navel), the front of the thighs or – with help – the upper arm. Change the site every time; do not inject into red, hardened or scarred skin. Wipe the site with alcohol and let it dry.
- Step 9
Inject
Gently lift a skin fold with two fingers. Insert the needle swiftly at a 90-degree angle, or rather 45 degrees if you have very little subcutaneous fat. Push the plunger slowly all the way down, wait 5–10 seconds, pull out the needle and only then release the skin fold. Do not rub.
Never reuse the syringe or put the cap back on – put it straight into the sharps bin.
Common mistakes
- Using tap water, saline from a nasal spray or “just any” water
- Shaking the vial vigorously or spraying water forcefully onto the powder
- Using syringes more than once – the needle becomes blunt and unsterile
- Reading at the end of the plunger instead of the front edge of the stopper
- Using U-40 syringes (veterinary) with a U-100 calculation
- Not noting the concentration and guessing later
- Using cloudy solution anyway
When to see a doctor
- Redness, swelling, warmth, pain or pus at the injection site
- Fever or chills after an injection
- Shortness of breath, facial swelling or a rash all over the body – call 112 immediately
In an emergency: 112 (EU emergency number).
FAQ
How do I reconstitute a peptide vial with BAC water?
Disinfect both stoppers, draw up the planned amount of bacteriostatic water and let it run slowly down the glass wall into the powder vial. Then swirl gently – do not shake – until the solution is clear, and label it.
Why shouldn't you shake the vial?
Vigorous shaking creates foam and mechanical stress. This can damage delicate peptides. Gentle swirling or rolling is enough to dissolve the powder.
What is the difference between BAC water and sterile water?
Bacteriostatic water contains 0.9 % benzyl alcohol, which inhibits the growth of germs after opening. Sterile water without additives is intended for single use.
How do I read a U-100 insulin syringe?
100 units equal 1 mL, so 1 unit is 0.01 mL. You read it at the front edge of the black stopper.
At what angle do you inject subcutaneously?
With short insulin needles usually at a 90-degree angle into a gently lifted skin fold; in very slim people more like 45 degrees.
Can I use the insulin syringe more than once?
No. The needle becomes blunt after one puncture and is no longer sterile. This increases pain and the risk of infection.
This article does not replace medical advice. It gives no dosing recommendations. As of September 2026.