How to reconstitute peptides
7 min read · Updated September 2026 · MY PEPTIDES Research Team
Key facts
Reconstituting a peptide means mixing the lyophilized (freeze-dried) powder with a liquid so it can be measured accurately. The standard reconstitution solution for research work is bacteriostatic water, which contains a small amount of benzyl alcohol so a vial can be drawn from more than once. The procedure is short: bring everything to room temperature, swab the stoppers, add a measured volume of bacteriostatic water slowly against the inside wall of the vial, swirl gently without shaking, then store the reconstituted vial refrigerated at 2-8°C and out of light. The amount of water you add sets the final concentration, so working it out first with a peptide calculator matters. One US-specific point runs through the whole guide: many of the compounds we supply for the US market ship pre-mixed as a solution, so for those vials there is nothing to reconstitute at all. Each compound is synthesized in our own UK laboratory and re-tested in a US laboratory before a US batch ships. This page covers the steps and the common mistakes. It is for laboratory research handling only, describes no dosing or use in humans or animals, and concerns compounds that have not been evaluated by the FDA.
Reconstituting a peptide means mixing the freeze-dried powder with a liquid so you can measure it. It takes about two minutes once you have done it a few times, and the steps below cover it start to finish, along with the mistakes that trip people up. One US-specific note before you start: many of the compounds we supply for the US market ship pre-mixed as a solution, so for those vials there is nothing to reconstitute at all (more on that at the end).
Research use only. This is a laboratory handling reference. It does not describe dosing, administration, or use in humans or animals, it makes no therapeutic claims, and the compounds discussed have not been evaluated by the FDA.
What "reconstitution" actually means
Most research peptides are supplied lyophilized, which means freeze-dried into a solid powder. Powder is stable for storage, but you cannot measure a powder accurately, so before use it has to be dissolved into a liquid. That dissolving step is reconstitution. The liquid you add is the reconstitution solution, and for research work that is almost always bacteriostatic water.
Bacteriostatic water is sterile water with about 0.9% benzyl alcohol added. The benzyl alcohol slows bacterial growth, which is what lets you draw from the same vial more than once over a research period. Our bacteriostatic water guide covers why that matters and how it differs from plain sterile water.
Do our US vials even need this?
Often not. Every vial we ship to US laboratories arrives pre-mixed as a solution at a known concentration, prepared under controlled conditions and HPLC-verified, so there is no powder to reconstitute and no bacteriostatic water to source. If that is what you ordered, skip the procedure below and simply refrigerate the vial at 2-8°C on arrival. The steps that follow apply when you are working from lyophilized powder, ours or another supplier's, and they are worth getting right, because reconstitution is the stage where most avoidable variability enters an experiment.
What you need
- The peptide vial (a lyophilized powder)
- Bacteriostatic water, your reconstitution solution
- A syringe to draw and add the water
- Alcohol swabs
The steps
1. Bring everything to room temperature. Take the peptide vial and the bacteriostatic water out and let them sit until they are no longer cold. Cold vials and cold liquid do not mix as cleanly, and condensation on a cold vial adds moisture you do not want.
2. Clean the stoppers. Wipe both rubber stoppers with an alcohol swab and give them a second to dry before you pierce them.
3. Work out your water volume first. Decide how much bacteriostatic water you are adding before you touch anything, because that number sets your final concentration. If you are not sure, run it through the peptide calculator so the concentration lands where you want it.
4. Draw the water. Pull your measured volume of bacteriostatic water into the syringe.
5. Add it slowly, against the wall. Push the needle through the stopper and let the water run down the inside wall of the vial. Slow is the whole trick. Firing it straight onto the powder can damage the peptide.
6. Swirl, do not shake. Set the vial down and roll it gently between your fingers until the powder fully dissolves and the liquid goes clear. Shaking foams the solution and stresses the peptide, and it gains you nothing.
7. Store it cold. The reconstituted vial goes in the refrigerator at 2-8°C, out of direct light, and is used within your research window. See how to store research peptides for the detail.
Mistakes to avoid
- Shaking the vial. Swirl instead, every time.
- Spraying water straight onto the powder rather than down the wall.
- Guessing the water volume and ending up with a concentration you cannot measure cleanly.
- Leaving the reconstituted vial at room temperature. Once it is in solution it belongs in the refrigerator, and it must not be frozen, because freeze-thaw cycling degrades a peptide already in solution.
Concentration is the part people get wrong
The same peptide reads as very different numbers on a syringe depending on how much water you used. Add 1 mL to a 5 mg vial and you get 5 mg/mL; add 2 mL and you get 2.5 mg/mL. Get the water wrong and every measurement after that is off. Doing the arithmetic before the powder ever touches liquid is the difference between clean data and a vial you have to discard. The peptide calculator does it for you.
The shortcut: our pre-mixed US vials
Reconstitution is the step where avoidable variability creeps in: water choice, added volume, mixing technique, and the delay before first use all differ between benches. That is why the compounds we supply for the US market ship as pre-mixed solutions at a known concentration, prepared under controlled conditions and released against a batch-specific Certificate of Analysis, with purity confirmed by HPLC and identity by mass spectrometry. Every compound is synthesized in our own UK laboratory, and each US batch is verified in a US laboratory before it is dispatched cold-chain, with tracked delivery across the United States next business day, priced in US dollars and payable by Visa, Mastercard or Apple Pay. Store the vial refrigerated at 2-8°C on arrival, not frozen. If that suits your work better, browse the shop and check the supply format on each product page.
Frequently asked questions
- What liquid is used to reconstitute peptides?
- Bacteriostatic water, which is sterile water with about 0.9% benzyl alcohol. The benzyl alcohol lets you draw from the same vial more than once, which is why it is the standard reconstitution solution for research peptides. Plain sterile water works but is really single-use.
- Do I need to reconstitute the vials I buy from you in the US?
- Usually not. The compounds we supply for the US market ship pre-mixed as a solution at a known concentration, so there is no powder to reconstitute and no bacteriostatic water to add. Just refrigerate the vial at 2-8°C on arrival. The steps here apply when you are working from lyophilized powder instead.
- How much bacteriostatic water should I add to a peptide vial?
- It depends on the concentration you want, not on a fixed rule. More water makes the solution easier to measure but more dilute; less water concentrates it. Work out the volume before you add anything, using a peptide calculator, so the final concentration is one you can measure cleanly.
- Why can you not shake a peptide vial?
- Peptides are delicate. Shaking foams the solution and can degrade the compound. Swirling gently gets the powder fully into solution without that stress, and it takes only a little longer.
- How long does a reconstituted peptide last?
- Keep the reconstituted vial refrigerated at 2-8°C and out of light, do not freeze it, and use it within your research window. The lyophilized powder lasts far longer, which is why peptides are shipped as powder and reconstituted only when needed.
- Are these research peptides FDA-approved?
- No. They are supplied strictly for in-vitro laboratory research, are not for human or veterinary use, and have not been evaluated by the FDA. This page covers laboratory handling only and contains no dosing or medical advice.