How to reconstitute peptides

What the powder in the vial is, how it is mixed, and how to turn a dose in micrograms into a mark on a syringe.

The short version

1. A peptide vial holds a fixed weight of freeze-dried powder, for example 5 mg.
2. You add a measured volume of bacteriostatic water, for example 2 mL.
3. That gives a concentration: 5 mg in 2 mL is 2.5 mg per mL.
4. The dose you want, divided by the concentration, is the volume to draw.

The calculator does this arithmetic for you. The rest of this page explains each part so you can check it yourself.

What you are working with

Lyophilized powder

Most peptides are sold freeze-dried (lyophilized) because they break down in liquid. The vial may look almost empty, or hold a small white disc or film. The label states the amount by weight, usually in milligrams.

Bacteriostatic water

Bacteriostatic water for injection is sterile water with 0.9% benzyl alcohol added as a preservative, which slows bacterial growth in a vial that is entered more than once. It is different from plain sterile water, which has no preservative and is meant for single use. Multi-dose vials of bacteriostatic water are generally labeled to be discarded 28 days after first use.

The U-100 insulin syringe

Insulin syringes are marked in units, not millilitres. On a U-100 syringe, 100 units equal 1 mL, so one unit is 0.01 mL. They come in three common sizes: 1 mL (100 units), 0.5 mL (50 units) and 0.3 mL (30 units). The smaller sizes have wider spacing between marks, which makes small volumes easier to read.

“Units” on the syringe measure volume only. They say nothing about how much peptide is in that volume until you know the concentration.

Mixing, step by step

This describes the general handling steps that product instructions and pharmacy practice have in common. Where a product comes with its own instructions, follow those.

1. Wash your hands and work on a clean surface.
2. Let the vial reach room temperature if it has been refrigerated.
3. Wipe both rubber stoppers, on the peptide vial and the water vial, with an alcohol swab and let them dry.
4. Draw up the water you have decided to add, using a new sterile syringe.
5. Add the water slowly, aiming the stream at the glass wall of the vial so it runs down the side onto the powder.
6. Swirl gently until the liquid is clear. Do not shake. Some peptides take a few minutes to dissolve fully.
7. Check the solution. It should be clear with no particles. Cloudiness or floating specks are a reason not to use it.
8. Label the vial with the date and the concentration you made, then refrigerate it.

The dose maths

Three numbers decide everything: the peptide in the vial, the water added, and the dose wanted.

Worked example

A 5 mg vial, 2 mL of water added, and a dose of 250 mcg:

• Concentration: 5 mg ÷ 2 mL = 2.5 mg per mL, which is 2,500 mcg per mL.
• Volume: 250 mcg ÷ 2,500 mcg per mL = 0.1 mL.
• Syringe: 0.1 mL × 100 = 10 units.
• Doses in the vial: 5,000 mcg ÷ 250 mcg = 20.

Try your own numbers:

Choosing how much water to add

The amount of water does not change the dose. It changes how much liquid that dose takes up. Pick an amount that puts your dose on a mark you can read accurately:

• Too little water and the dose becomes a tiny volume, such as 1 or 2 units, where a small misreading is a large percentage error.
• Too much water and the dose may not fit in the syringe, or the vial may not hold it.
• Round numbers help. A concentration where your dose lands on 10, 20 or 25 units is easier to draw the same way every time.

Storage

• Before mixing: freeze-dried peptides are generally kept refrigerated or frozen and away from light. Follow the label.
• After mixing: keep the vial refrigerated, not frozen, and away from light. How long a mixed peptide stays stable varies widely by peptide, and for most unapproved peptides it has not been formally established.
• Never reuse syringes or needles, and dispose of them in a sharps container.

Common mistakes

• Confusing mg and mcg. 1 mg is 1,000 mcg. This is the error that produces a dose a thousand times too large or too small.
• Treating syringe units as a dose. “10 units” means 0.1 mL, nothing more. The dose depends on the concentration you made.
• Assuming the vial holds what the label says. Products sold for research are not regulated for purity, identity or the amount in the vial. No calculation can correct for that.
• Using a non-U-100 syringe. The unit maths on this page only applies to U-100 insulin syringes.

Common questions

This guide explains measurement and general handling. It is not medical advice and does not say whether any substance or dose is appropriate for you. For per-peptide doses and their approval status, see the dosing chart.

Reference only, not medical advice. Doses marked FDA-approved come from the US prescribing label. Doses marked Not approved are ranges reported from small studies or community use and have not been established as safe or effective in humans. Check anything here with a licensed clinician before acting on it. Read the full disclaimer.