Three enemies, one direction
Heat, light and water are the forces that dismantle a peptide, and they only ever work in one direction. Warmth accelerates every degrading reaction; ultraviolet light attacks bonds and sensitive side chains directly; and water enables hydrolysis, which is why the dry form so dramatically outlives the dissolved one.
Lyophilised powder in a sealed vial is the compound at its most defensible: no solvent, minimal oxygen, one container between the material and the world. Kept cold and dark, sealed vials measure their stability in months to years.
Reconstitution changes the game permanently. The moment water enters, hydrolysis begins its slow work and every subsequent needle through the septum adds risk. A reconstituted vial is not spoiled, it is simply on a clock that the sealed vial was not.
Nearly every question we receive about peptide storage and shelf life comes back to those three enemies plus the format the compound arrives in. Sealed powder is one case. A pre-filled pen or a nasal spray is already in solution when it reaches you, so the reconstituted rules apply from the day of delivery rather than from the day water goes in.
Four conditions, in priority order
Follow these and storage stops being a variable in your work.
Reading the dates honestly
The expiry on a sealed vial assumes the storage conditions above; it is a promise about the compound under discipline, not under any circumstances. A vial that spent a summer week in a parcel locker has aged more than its label knows.
For reconstituted material, supplier guidance varies by compound, but the honest framing is weeks rather than months, refrigerated, with bacteriostatic water, and less than that for the compounds flagged as fragile on their product pages.
When a date and a doubt collide, the doubt wins. Peptides are replaceable; the confounded results of research run on degraded material are not. That asymmetry should settle every borderline case.
The literature supports the asymmetry rather than any particular date. Stability studies of lyophilised peptides indexed on PubMed repeatedly find the dry, sealed form holding its assay value across long intervals, while the same compounds in solution lose it on a timescale set by temperature, pH and sequence. That is why a supplier can state a shelf life for the sealed product and only hedge on the reconstituted one: the second number depends on what happened after delivery.
- Freeze a reconstituted vialIce crystals shear dissolved peptides. Freezing is for sealed powder only.
- Store in the fridge doorThe door is the warmest, most temperature-cycled shelf in the appliance.
- Leave vials in daylightWindow sills and bench tops under lab lighting both count. Dark means dark.
- Trust an undated open vialNo date means no clock, and no clock means the material is already a question mark.
The storage series
Two companion pages complete the picture.
About storage
The storage questions that reach our inbox.