How to Store Peptides
A freeze-dried powder and the same peptide in solution are two different storage problems. Powder is robust and solution is not, and the moment you add water you have changed which set of rules applies.
Powder and solution are not the same problem
This is the single thing worth understanding, and most storage questions answer themselves once it is clear.
Lyophilised powder is stable. Freeze-drying removes the water that degradation reactions need, which is why a peptide can be shipped as powder at all and why it tolerates ordinary temperatures for a long period.
A reconstituted solution is not stable in the same way. Adding water puts the water back. Hydrolysis, aggregation and microbial growth all become possible, and the benzyl alcohol in bacteriostatic water inhibits bacterial growth — it does not stop the chemistry and it does not sterilise anything you introduce.
So a vial has two lives with two different sets of conditions, and the dividing line is the moment you reconstitute it. How to reconstitute peptides covers the step itself.
By format
| Format | Before preparing | After preparing | Light |
|---|---|---|---|
| Lyophilised vial | Cool, dry, dark. Freezer for long holding. | Refrigerated, and its life is now short | Keep out of direct light |
| Pen | Arrives in solution — refrigerated from the start | Keep out of direct light | |
| Nasal spray | Arrives in solution — refrigerated from the start | Keep out of direct light | |
| Capsules | Cool, dry, sealed. No refrigeration needed. | Keep out of direct light | |
| Bacteriostatic water | Room temperature, sealed | No special requirement | |
The pattern is simple enough to state in one line: anything in solution belongs in a fridge, and anything dry does not need one. A pen and a nasal spray arrive in solution, so they start in the fridge. A capsule never goes into solution at all.
The three things that actually cause damage
Temperature cycling, not temperature. A vial held steadily at room temperature is in better condition than one moved in and out of a fridge a dozen times. Each cycle is a condensation event on the inside of the glass and a stress on the stopper seal. Pick a place and leave it there.
Light. Peptides vary in how photosensitive they are and the packaging is not a substitute for a dark shelf. Methylene blue is the clearest case in the range — it is a dye, strongly coloured because it absorbs light, and light is therefore exactly what it should be kept away from.
Agitation. Mostly a reconstitution problem, but it does not stop being one afterwards. A reconstituted vial rattling loose in a bag is being sheared. Keep it upright and keep it still.
Freezing: when it helps and when it does not
Powder, for long holding: a freezer is the right answer. There is no water in a lyophilised cake to form ice crystals, and cold slows everything that remains.
A reconstituted solution: freezing is not a way to extend it. Freezing a solution forms ice crystals, and ice crystals and the concentration gradients around them are a recognised mechanism of protein damage. Repeated freeze-thaw cycles are worse than either state.
The practical version: freeze it before you add water, or refrigerate it after. Do not reconstitute a vial and then freeze it to make the solution last.
How long does it last? Why we will not give you a number
This is the most-asked storage question on the site and the honest answer is that we are not going to invent a figure.
A shelf life is a measured property of a specific compound in a specific formulation at a specific temperature, established by stability testing. It is not a general property of peptides and it is not something that can be estimated from a category. Publishing "28 days in the fridge" across a catalogue of thirty-odd compounds, because that is the number people search for, would be making up data — and a made-up stability figure is worse than none, because it gets relied on.
What is authoritative is the label on the vial you have and the certificate of analysis for that batch. The CoA is available on request for anything we supply, batch by batch. Email us and we will send it; we do not post certificates publicly, because a certificate detached from the batch it belongs to is not evidence of anything.
What can be said generally, and is true regardless of compound: powder holds far longer than solution, cold holds longer than warm, dark holds longer than lit, and undisturbed holds longer than cycled.
How we dispatch, and what to do when it arrives
Orders placed before 2pm are dispatched the same working day on a tracked UK service. Vials go out as lyophilised powder, which is the state that tolerates transit — it is the reason the whole catalogue is built around powder rather than pre-made solutions.
On arrival: get it off the doormat and onto a shelf. Dry formats — vials, capsules — want somewhere cool, dry and dark. Anything that arrived already in solution, which means pens and nasal sprays, wants a fridge.
If a vial arrives cracked, with a compromised stopper, or with powder that looks wrong — melted, discoloured, shifted to one side as though it has been wet — stop and get in touch before you do anything else. Do not reconstitute it to find out. Quote the batch number from the label and we will pull the certificate of analysis for it.
What this page does not cover
There is no dose on this page, no protocol, no frequency, no unit conversion and no click count, and there is none anywhere else on this site either.
Everything we supply is an unlicensed research compound. It carries an analytical specification — the compound, the quantity, the purity determined by HPLC — and not a Summary of Product Characteristics. A specification describes what is in a vial. It is not a short leaflet, and publishing a human dose alongside it would be promoting an unlicensed compound for human use. We are not willing to do that, and a calculator that returns millilitres to administer rather than a concentration is the same thing with extra steps.
What we will give you is the chemistry: the concentration arithmetic, in both directions, and the conditions a peptide is stable under. If that is not what you came for, nothing further on the site will help, and are peptides legal in the UK explains the category these compounds sit in.
Supply note. Peptiq supplies research compounds for laboratory research use only. This page covers the handling of a material — concentration, temperature and light. It contains no dosage, protocol or administration guidance of any kind, and we do not publish any.
Frequently asked questions
Does a lyophilised peptide vial need refrigerating?
Not before it is reconstituted. A freeze-dried vial is stable kept cool, dry and out of direct light, and a freezer is appropriate for long holding. Once reconstituted it should be refrigerated.
Should a peptide pen be kept in the fridge?
Yes. A pen arrives already in solution rather than as powder, so it belongs in a fridge from the start. The same applies to nasal sprays.
Can you freeze a reconstituted peptide?
Freezing a solution forms ice crystals, which is a recognised mechanism of protein damage, and repeated freeze-thaw cycles compound it. Freeze the powder before reconstitution if you need to hold it; refrigerate the solution afterwards.
How long does a reconstituted vial last?
We do not publish a figure. A shelf life is a measured property of a specific compound and formulation established by stability testing, not a general property of peptides. The label on your vial and the certificate of analysis for that batch are the authority, and the CoA is available on request.
Do capsules need to be refrigerated?
No. Capsules are a finished solid form and never go into solution. Cool, dry, sealed and out of direct light is sufficient.