Peptide storage: fridge, freezer, or room temperature.

Two states, two different answers. Sealed lyophilised powder is the stable form and tolerates the most. Once you add water you have made a solution, and a solution in a vial has a much shorter and much less forgiving life.

Most storage advice circulating online collapses those two into one number. They are not one number, and the difference between them is where most degradation happens.

Powder and solution are not the same problem

Freeze drying removes the water, and water is what most degradation reactions need. That is the entire reason peptides ship as powder. Adding the diluent starts a clock that was not running before.

Freezing a reconstituted vial is usually the wrong move

The instinct is that colder is safer for longer. For a solution it often is not. Freezing and thawing concentrates solutes as ice forms and puts the peptide through an interface it did not face in the fridge, and repeated freeze thaw cycles are a recognised cause of loss for peptides in solution.

If a vial is genuinely going into long term storage, freezing it once and thawing it once is a different proposition from a vial that goes in and out of the freezer between doses. The second pattern is the one to avoid.

The freeze-thaw literature worth reading is mostly on proteins and antibodies rather than on the peptides in this catalogue, and the mechanisms it describes are aggregation at the ice-water interface, cold denaturation, and the pH and salt concentration shifts that happen as ice forms. Whether a given short peptide is affected the same way is not established for most of them. That is a reason to avoid repeated cycling rather than a measurement of what it costs you.

Light, and the part people skip

Several amino acids are photosensitive, which is why vials are often amber and why the fridge door is a worse place than the middle shelf. It is also why a vial left on a windowsill during reconstitution has already had a worse day than one that stayed in the box.

The fridge door is worth naming for a second reason: it is the warmest part of the fridge and the part that swings most in temperature every time the door opens. Middle shelf, at the back, is duller and better.

Why we will not give you one number

Every "reconstituted peptides last 28 days" style claim you see is a generalisation across molecules that behave very differently. Some are stable in solution for weeks. Some lose meaningful activity much faster. The honest answer is per compound, and for a large number of research peptides the published stability data in the exact conditions you are storing them simply does not exist.

That is a real gap, not a coy answer. Where it exists we hold it per compound in the app. Where it does not, we say so rather than picking a number that sounds authoritative.

Practical rules that hold up

Keep sealed powder cool, dry and dark, and follow the supplier's instruction where you have one. Refrigerate reconstituted vials at 2 to 8 °C, on a shelf rather than in the door. Do not cycle a working vial through the freezer. Keep it out of light and out of the warm. Write the reconstitution date on the vial, because a month later you will not remember it and guessing is the same as not knowing.

And treat any single duration you read as a claim that needs a source attached, including the ones that sound confident.