The two states, two different rules
Every peptide has two storage phases: as a dry, lyophilised powder, and after reconstitution into liquid. The powder form is more stable and tolerates brief temperature excursions better. Once mixed with water, the rules tighten considerably.
General ranges
Refrigeration at 2-8°C is the standard recommendation for both states, though powder often has a wider tolerance for short periods outside that range (such as during shipping) than a reconstituted vial does.
What accelerates degradation
Heat, light and time are the three factors that matter most. Warmer temperatures speed up the chemical breakdown of the peptide chain. Direct light exposure adds to that. And even under ideal storage, a reconstituted peptide has a finite window, typically a matter of weeks, not months.
Freezing isn’t a shortcut
It might seem like freezing would extend shelf life indefinitely, but repeated freeze-thaw cycles can damage a peptide’s structure through ice crystal formation. Most guidance for injectable peptides recommends refrigeration, not freezing, for this reason.
A practical routine
Keep vials refrigerated, away from light, upright, and away from the fridge door. Label reconstituted vials with the date they were mixed, and treat any vial that’s spent an extended period at room temperature as compromised rather than assuming it’s still fine.