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Temperature bands, the four things that actually cause degradation, and how long each format realistically lasts.
Where a peptide should sit depends almost entirely on whether it is dry or in solution.
There is no single correct storage temperature, but there is a clear ordering: colder is more stable, and the penalty for being warm accumulates. The practical question is which band a given vial belongs in today, not what the theoretical optimum would be.
Deep frozen
Archival storage. Worth it for fragile sequences or anything being held for years.
Frozen
The default for lyophilised powder held long term. A standard freezer reaches this.
Refrigerated
Where a reconstituted vial lives, and where powder sits once it is in use.
Ambient
Fine in transit and while you handle it. Not a place to leave anything.
The same compound can be stable for two years or for three weeks depending on which state it is in.
As a lyophilised powder, a peptide is remarkably robust. There is no water for hydrolysis to work with and very little molecular mobility, so at −20 °C most sequences hold for a year or two, and at −80 °C considerably longer. What it is vulnerable to is moisture, which is why the seal matters more than the exact temperature.
In solution, everything speeds up. The molecule is mobile, surrounded by water, and exposed to whatever entered when the stopper was pierced. Refrigerated at 2-8 °C, roughly four weeks is a sensible planning figure. That is not a hard expiry - a vial that has stayed sterile and looks completely clear is often good for longer - but it is the number to build a routine around.
The practical consequence is that reconstitution is a commitment. It is worth doing when you are ready to use the compound, not in advance because it is convenient.
Four stressors do nearly all of the damage, and each has an unglamorous countermeasure.
These are not independent. Warmth makes oxidation faster, moisture makes warmth worse, and a vial that has been shaken has more surface area for everything else to act on. Getting the storage right is mostly about not stacking them.
Freezing extends life; repeatedly thawing spends it.
Each freeze-thaw cycle forms and melts ice crystals through the solution, and the mechanical stress of that is real. A vial that is frozen once and thawed once has lost very little. One that has been in and out five times has lost meaningfully more, even though it spent almost all of that time at the correct temperature.
The fix is to decide the portion size before freezing rather than after. Aliquot into single-use volumes, freeze those, and thaw only what you are about to use. A vial you never refreeze cannot accumulate cycles.
It is also worth knowing that frost-free freezers work by cycling their temperature up periodically to prevent ice build-up. That is convenient for food and quietly hostile to anything you are storing long term - a manual-defrost unit holds a genuinely steadier temperature.
Time at ambient temperature during shipping is normal and not a problem.
Lyophilised powder tolerates a shipping window at room temperature without meaningful loss - this is exactly why peptides are supplied dry. A package that arrives warm has not been ruined.
What matters is what happens next. Inspect the vials on arrival, check that seals and stoppers are intact, and move everything into proper storage rather than leaving it on a bench. If a vial has come out of a cold shipper, let it equilibrate before you open it so condensation does not form on the cold glass.
Realistic working windows by format.
Lyophilised powder, frozen
−20 °C for routine long-term holding; −80 °C for archival or fragile sequences.
Lyophilised powder, refrigerated
Fine for a vial in active use. Keep it sealed and dry.
Reconstituted, refrigerated
Often longer if it has stayed sterile and clear, but treat 28 days as the working assumption.
Nasal solution, refrigerated
Same clock as any other solution. The pump does not preserve anything.
These windows vary by compound - some sequences are markedly more fragile than others. Where a specific product has its own guidance, it is on that product's page and takes precedence over this table.
If you remember nothing else from this page.
Working out the concentration to put on that label is covered in the reconstitution guide.
General laboratory reference material for research use. Not medical advice. Where a specific product carries its own storage guidance, follow that instead.