It depends on the state and the duration
A lyophilised (powder) vial left at room temperature for a short period, hours rather than days, is generally considered more forgiving than a reconstituted vial in the same situation, since removing the water slows most degradation reactions significantly.
Short lapses versus long ones
A few hours at typical room temperature, the kind that can happen during a delivery, is commonly treated as low risk for powder form. Multiple days at room temperature, or any exposure to genuinely hot conditions (a warm car, direct sunlight), is treated far more cautiously, especially for a reconstituted vial.
What’s actually happening chemically
Heat speeds up the breakdown of the peptide’s chain. This is a gradual process, not an instant one, which is why a brief lapse doesn’t necessarily ruin a vial the way, say, leaving milk out overnight would spoil it. But the effect is cumulative and not reversible by refrigerating again afterward.
Refrigerating again after a lapse
Putting a vial back in the fridge after a temperature lapse stops further degradation from that cause, but it doesn’t undo whatever degradation already happened. The vial may still be usable, just potentially with somewhat reduced potency depending on how long and how hot the lapse was.
The practical takeaway
A short lapse is unlikely to be a serious problem, particularly for powder. A longer lapse, or any exposure to real heat, is a reason to treat the vial with more caution rather than assume it’s unaffected.