In this article10 sections
Sealed, freeze-dried peptides typically show no measurable loss for about four weeks at room temperature, so a few days in the post is fine. For keeping: freezer for years, fridge for about a year. Once mixed with water, keep it in the fridge and use it within four weeks.
Peptides are chains of amino acids joined by amide bonds, and every one of those bonds is a site for hydrolysis. Add side chains that oxidise (methionine, cysteine, tryptophan), residues that deamidate (asparagine, glutamine) and sequences that aggregate, and you have a molecule whose purity is a function of how it has been kept. Correct peptide storage is not fussiness; it is the difference between a 99% material and one that has quietly drifted to 90% by the time it is used. This guide sets out how to store peptides at each stage, from the sealed vial to the reconstituted solution, and answers the most-asked question: how long peptides last at room temperature.
- Sealed lyophilised peptide: typically stable for several weeks at room temperature (up to about 25 °C), a year or more at 2 to 8 °C, and two to three years at -20 °C.
- Those figures come from manufacturer stability data; they assume the vial is sealed, dry and out of direct light.
- Reconstituted peptide in solution: days to a few weeks refrigerated, depending on the sequence. Water restarts every degradation route.
- Methionine, cysteine and tryptophan residues oxidise; asparagine and glutamine deamidate; Asp-Pro bonds hydrolyse. Sequences without these are more forgiving.
- Shipping at ambient temperature for a few days does not measurably degrade a sealed lyophilised vial.
How should you store peptides? The quick version
In shortPowder: freezer or fridge, in the dark. Mixed: fridge, use within four weeks.
Long term: 2 to 3 years.
In use over months: about a year.
Transit only: about 4 weeks.
Use within 4 weeks. Don't refreeze.
Light damages some peptides.
Lot number and date mixed.
From this guide.
Sealed and lyophilised: minus 20 °C for the long term, 2 to 8 °C for months, in the dark. Reconstituted: 2 to 8 °C, in the dark, used within four weeks, never repeatedly frozen. Label everything. That is essentially all of peptide storage, and it is what keeps the purity on the certificate true for the life of the vial. All products on this site are supplied for laboratory research only under our research use policy.
How long do lyophilised peptides last at room temperature?
In shortSealed powder: about four weeks with no measurable loss. Fine for posting, not for keeping.
Typical stability data for sealed lyophilised peptides, as set out in this guide. Robust sequences often last longer.
Room temperature, up to about 25 °C. Stability data for sealed lyophilised peptides typically shows no measurable purity loss over four weeks at 25 °C, and many suppliers extend that to eight or twelve weeks for robust sequences. This is the band that matters for transit: a vial spending three days in the post in a British summer is nowhere near the limit. It is not the band for storage, because the small losses compound over months and because summer rooms exceed 25 °C.
Refrigerated, 2 to 8 °C. The usual recommendation for vials in active use over the coming months. A year is a conservative figure for most sequences; some are specified for two.
Frozen, -20 °C. Long-term storage. Two to three years is the standard specification, and re-testing of older lots often finds purity unchanged well beyond that. Deep-frozen storage at -80 °C adds little for lyophilised powder; it is solution that benefits from it.
How to store unopened powder vials
In shortCold, dark and dry. The freezer for long term.
Freeze-dried peptide in a crimp-sealed vial is the most stable form the material will ever be in. Water is the main agent of degradation, and lyophilisation removes it. In this form the two things that matter are temperature and light.
For storage beyond a few weeks, keep sealed vials at minus 20 °C. At that temperature most peptides show no measurable loss of purity over years. For shorter periods, 2 to 8 °C in a laboratory refrigerator is adequate; most lyophilised peptides tolerate refrigerated storage for many months and room temperature for several weeks, which is why a sealed vial can travel by post in an insulated pouch without harm. The exceptions are copper peptides and any sequence containing methionine or cysteine, which we recommend refrigerating on arrival.
Keep vials in their box or in an opaque container. Tryptophan, tyrosine and histidine absorb ultraviolet light and photodegrade. A vial on a lit bench for a day is not a disaster; a vial on a windowsill for a month is.
Do not open a sealed vial you are not about to use. Each opening admits humid air, and a lyophilised cake is hygroscopic. If you need to weigh out part of a vial, do it once, in a dry environment, and reseal the remainder under parafilm.
How to store peptides once mixed
In shortFridge, dark, and use within four weeks. Don't keep freezing and thawing it.
Once the peptide is in solution the clock starts. Hydrolysis and oxidation proceed at rates that depend on temperature, pH, concentration and the specific sequence. The practical rules are these.
Store reconstituted vials at 2 to 8 °C, protected from light, and plan to use them within four weeks. That window aligns with the 28-day multi-dose life of bacteriostatic water once its stopper has been punctured and is conservative for most sequences. Some peptides remain within specification for longer; some, particularly those prone to aggregation, do not. If a protocol runs longer than four weeks, reconstitute a fresh vial rather than extending the old one.
Do not freeze a reconstituted vial that you intend to keep drawing from. Each freeze-thaw cycle concentrates solutes as ice forms, shifts pH locally and stresses the peptide; three or four cycles can cost several percent of purity. If a solution must be kept for longer than four weeks, split it into single-use aliquots in sterile tubes, freeze them once at minus 20 °C or below, and thaw each aliquot once.
Keep the vial in the body of the refrigerator, not the door. Door temperatures cycle every time it opens and can exceed 8 °C for long enough to matter.
Add and every degradation route restarts. Refrigerated solution of a robust peptide is usually good for a few weeks; sensitive sequences are good for days. The benzyl alcohol in bacteriostatic water prevents bacterial growth but does nothing for chemical stability, which is why our bacteriostatic water article and product storage notes give separate figures for sealed and reconstituted material. Solution should be stored at 2 to 8 °C, kept out of light, and never repeatedly frozen and thawed; if it must be kept longer, it is aliquoted and frozen once. Our reconstitution guide covers the technique.
How can you tell if a peptide has gone off?
In shortSticky powder or cloudy liquid are bad signs, but a vial can look fine and still have degraded.
It has absorbed moisture.
Oxidised.
The peptide has clumped.
Discard.
Copper has come loose.
Can still have degraded. Only HPLC can tell.
From this guide.
Lyophilised powder that has collapsed into a sticky film, or that has turned yellow or brown, has absorbed moisture or oxidised. A reconstituted solution that has become cloudy, developed particles, or changed colour should be discarded. A copper peptide solution that has gone from blue to green or brown has lost its copper coordination. For anything ambiguous, a quick run against the lot's will show whether the purity has moved.
You cannot tell by looking. A collapsed, sticky or discoloured cake indicates moisture damage, and a cake that dissolves cloudy indicates aggregation, but a vial can look perfect and have lost purity to oxidation or deamidation, both of which are invisible. The only measurement is HPLC, which is what the certificate of analysis reports and why the certificate is dated and tied to a lot; our guide to reading one explains the purity figure. For a laboratory that needs to know, the answer is to re-test, and for everyone else the answer is to keep the vial sealed, cold and dark and to use it within the specification.
Is it OK if peptides arrive warm?
In shortYes. A few days in the post doesn't harm sealed powder.
Well inside the room-temperature band.
Within a few hours.
Frozen stock and a recent certificate.
From this guide.
We ship lyophilised vials in a plain insulated pouch with a cool pack for compounds that specify refrigerated storage. The insulated pouch is not a refrigerator; it slows warming for the 24 to 48 hours the parcel is with Royal Mail. On arrival, move vials to the correct storage temperature within a few hours. A lyophilised peptide that spent a day at room temperature in transit has lost nothing measurable.
Ambient shipping is not a corner cut. A sealed lyophilised vial in the post for two or three days is within the room-temperature band by a wide margin, and adding a cold pack changes nothing except the risk of condensation if the vial is opened cold. What matters is what happened before dispatch: whether the vendor stored stock frozen or on a warehouse shelf for a year, and whether the certificate is recent. Every vial ALTA PEPTIDES ships is held frozen in UK stock, published with its lot certificate of analysis, and dispatched the same working day before 1pm, with the storage specification for that product on its page and on the label.
Everything above is the quick version. The sections below go deeper.
Why freeze-dried peptides keep so well
In shortWater is what breaks peptides down. Take it out and they keep for years.
Almost every way a peptide degrades needs water. Hydrolysis of the peptide bond is a reaction with water by definition. Deamidation, in which asparagine or glutamine side chains lose ammonia and the sequence changes charge, proceeds through a water-mediated intermediate. Aggregation needs the molecules to move, which they do not in a dry cake. Lyophilisation removes the water by freezing the solution and pulling the ice off under vacuum, leaving an open, porous solid with a residual moisture content of a few percent or less. The vial is then sealed under nitrogen, which also removes most of the oxygen that drives oxidation. What is left is a chemically quiet system in which the remaining reactions run thousands of times more slowly than in solution.
What shortens shelf life
In shortHeat, moisture, light, air and repeated freeze-thaw.
Moisture. The single biggest threat. A vial opened at room temperature, or a stopper pierced and left, lets humid air in, and the cake absorbs water and begins to degrade as if it were in solution. Vials that have been in the freezer must reach room temperature before opening, or condensation forms on the cold powder.
Light. Tryptophan and tyrosine absorb ultraviolet, and photodegradation is real for sequences that contain them. Vials are stored in their boxes or in amber secondary containers.
Sequence. Methionine and cysteine oxidise; tryptophan oxidises and photodegrades; asparagine followed by glycine deamidates fastest; an aspartate-proline bond hydrolyses more readily than any other. A short peptide with none of these, GHK for example, is close to indefinitely stable dry. BPC-157 has none of the fragile residues and is unusually robust. Retatrutide and other GLP-1-class peptides carry oxidisable residues and fatty-acid chains and are specified more conservatively.
Counter-ion and excipients. Peptides are supplied as trifluoroacetate or acetate salts, sometimes with mannitol as a bulking agent. Acetate salts are slightly more stable than TFA salts over long storage; mannitol helps the cake hold its structure. The certificate of analysis states the net peptide content, which accounts for both.
Which peptides need extra care?
In shortSome sequences oxidise or clump more easily and need colder, darker storage.
GHK-Cu is stable in solution but the copper complex is light-sensitive; keep it in the dark. MOTS-c and epitalon are short, robust sequences that store well. BPC-157 is notably stable, including in acidic conditions, a property that comes up in its research history. TB-500 is longer and benefits from careful handling to avoid shear. Semax and Selank contain proline-rich motifs that resist enzymatic cleavage but are as susceptible to oxidation as any other peptide, so the general rules apply.
Questions people ask
How long do lyophilized peptides last at room temperature?
Sealed and dry, weeks rather than days; most manufacturer data supports up to about four weeks at 25 °C without measurable loss, and longer for robust sequences. For storage rather than transit, refrigerate or freeze.
Do peptides need to be refrigerated during shipping?
No. Lyophilised powder in a sealed vial tolerates ambient transit of a few days. Cold packs are added for reconstituted or sensitive products, not for standard lyophilised vials.
Can I refreeze a peptide vial?
Sealed lyophilised powder can be moved between freezer and fridge without harm. Reconstituted solution should not be repeatedly frozen and thawed; aliquot it instead.
How can I tell if a lyophilised peptide has degraded?
You cannot by eye. A collapsed or discoloured cake suggests moisture ingress, but chemical degradation is invisible. HPLC is the only reliable check, which is why the certificate is dated and lot-specific.
Information, not advice. This article summarises published research; nothing here is guidance on human or veterinary use. Products are sold under our research use policy.
