How to store peptides

Research peptides are almost always sold lyophilised: freeze-dried into a powder or a small solid “cake” at the bottom of a sealed vial. In that dry state most peptides are fairly robust. Once water is added (reconstitution) the clock starts running much faster, because water lets the reactions that break peptides down actually happen.

So storage advice splits in two: how to keep the dry vial, and how to keep it once mixed. The general rules below apply to most peptides; where a specific peptide is known to be less stable, its page in our peptide guides says so. Always check the supplier’s own storage instructions too; a supplier that gives none is telling you something (see how to spot an unreliable supplier).

These are general rules that apply to most peptides. The supplier’s instructions and any stability data for a specific peptide take priority.

Knowing what degrades peptides makes the rules easier to remember:

• Heat speeds up every degradation reaction. This is why freezer storage extends shelf life and why a parcel left in a hot van matters.
• Moisture. Many freeze-dried peptides are hygroscopic: they pull water from the air. Even a little moisture in a dry vial starts the slow chemistry that dry storage is meant to prevent.
• Oxygen. Peptides containing cysteine, methionine or tryptophan oxidise more readily.
• Light, particularly ultraviolet, can degrade some amino acids.
• Repeated freezing and thawing, which is especially hard on peptides in solution.
• Bacteria, once the vial has been opened and mixed. This is the reason bacteriostatic water exists.

Stability depends on the sequence. Peptides containing cysteine, methionine or tryptophan are prone to oxidation. Sequences with asparagine, particularly next to glycine, can deamidate in solution. Some hydrophobic peptides tend to clump together (aggregate), especially after shaking or repeated freezing. Cyclic peptides and those modified to resist breakdown are often more robust than short linear ones. This is why a single shelf-life figure for “peptides” is misleading, and why published stability data for a specific peptide, where it exists, beats general rules.

• Long term: in the freezer. Around −20 °C is the usual recommendation for keeping dry peptides for months or longer. Laboratories keeping reference material for years often use −80 °C.
• Short term: the fridge is fine. At 2–8 °C most dry peptides keep for weeks. A few days at room temperature, as in normal shipping, is generally tolerated by dry peptides; that is why they can be posted without refrigeration.
• Keep them dark and sealed. Leave vials in their box or an opaque container, with the stopper and seal intact until you need them.
• Let a cold vial warm up before opening. Opening a vial straight from the freezer lets moist room air condense inside it. Leaving it closed until it reaches room temperature avoids that.
• Avoid the fridge door and frost-free cycles where you can. The door warms every time it opens, and frost-free freezers cycle their temperature.

Once mixed, a peptide solution is far less stable than the powder it came from.

• Refrigerate it at 2–8 °C. Do not leave a mixed vial at room temperature.
• How long it keeps depends on the peptide. Some are stable in solution for weeks in the fridge; others lose potency much sooner. There is no single number that fits every peptide, and figures quoted online are often guesses. Our individual peptide pages note published stability data where it exists.
• Mixing liquid matters. Bacteriostatic water contains a preservative that suppresses bacterial growth, which suits vials used more than once. Plain sterile water has none, so a vial made with it should be treated as single-use. Our bacteriostatic water guide compares the two.
• Mix gently. Let the water run down the inside of the vial and swirl rather than shake. Vigorous shaking can cause some peptides to aggregate.
• Freezing a solution is a trade-off. Some labs freeze peptide solutions in single-use portions (aliquots) so each is thawed only once. Refreezing the same vial repeatedly is what does the damage.
• Label it. Write the date mixed and the amount of water added on the vial. The water volume decides the concentration: the peptide calculator converts it into mg per mL and syringe units.

• A dry cake that has collapsed, looks wet, or has turned sticky or discoloured.
• A solution that is cloudy, has particles or flakes, or has changed colour. Most reconstituted peptides are clear and colourless (copper peptides such as GHK-Cu are a known exception: they are blue).
• A powder that will not dissolve when it normally would.

None of these can be confirmed by eye. Only a laboratory test can say how much intact peptide remains; see third-party testing explained.

Check the parcel as soon as it arrives. Note whether it came with cold packs, and whether they were still cold. Check that each vial is sealed, that the batch number on the vial matches the certificate on the supplier’s site, and that the contents look like a dry, intact cake or powder. Then move the vials to the fridge or freezer straight away.

If anything is wrong, photograph it before opening and contact the supplier. Delivery speed and packaging are part of each supplier’s rating on PepFinder: see the fastest delivery ranking, and if you have ordered, a short review helps other buyers know what to expect.