The short version: once you mix a peptide with water it belongs in the fridge, at roughly 2–8 °C. Sealed, unmixed powder is more forgiving and survives short spells at room temperature, but for anything longer it also wants to be cold, and for long-term storage it is usually kept frozen. Heat is what does the real damage, so the warmer it gets, the shorter the safe window. Your own vial's instructions always win.
This trips almost everyone up at the start, because a vial goes through two very different lives — a dry, stable one before you mix it, and a much shorter, more fragile one afterwards. The rules are different for each, so it is worth separating them.
| State | Room temp | Fridge (2–8 °C) | Freezer |
|---|---|---|---|
| Sealed powder (lyophilised) | Tolerates short periods | Fine for weeks–months | Best for long storage |
| Reconstituted (mixed) | Only briefly — hours, not days | The normal home; days to a few weeks | Once only, to extend it |
These are general handling norms, not a guarantee for any specific compound. Exact numbers vary by peptide, purity and whether the water has a preservative.
Short, planned excursions are usually fine — letting a vial reach room temperature before use, or the day or two it spends in the post. The problems come from heat and time together: a vial left in a hot car, on a sunny windowsill, or forgotten warm for days. A reconstituted vial is far more sensitive to this than sealed powder. If in doubt, keep the excursion as short and as cool as you can, and write down when it happened so you are not guessing later.
In rough order of how much damage they do:
Sealed powder that spent a couple of warm days in transit is usually no drama — get it cold and carry on. A fridge outage of a few hours is similarly minor. The judgement call is a reconstituted vial that has been warm for an extended period; there is no way to test it at home, so weigh it up and, when unsure, start fresh. See the storage guide for travel and power-cut specifics.
Reconstituted HCG is kept refrigerated; the sealed form tolerates short room-temperature periods but is stored cold. Follow the instructions on your own vial — presentations differ.
Sealed powder freezes well. A mixed vial can generally be frozen once to extend it, but avoid repeated freeze–thaw cycles.
MK-677 is an oral small molecule, not a peptide, and is usually stored at room temperature away from heat and light. See what actually counts as a peptide.
The shelf-life reference table lists refrigerated and frozen figures for every compound in the library, with the method and limitations.