Does freezing a reconstituted peptide damage it?

One careful freeze usually isn't the problem. Repeated freeze and thaw is. Supplier handling guides from Sigma-Aldrich and GenScript both say to avoid repeated freeze-thaw cycles for peptide solutions, because each cycle degrades a little of the peptide. The damage comes from ice crystals, salt and pH shifting as water freezes out, and the peptide getting battered at the ice-water interface. Some also aggregate or oxidize there. The fix in those same guides: split the reconstituted solution into single-use aliquots before the first freeze, so you thaw only what you need and never refreeze the rest. GenScript suggests -20C for short-term and -80C for longer storage. Thaw gently at room temperature, not in hot water. How much a peptide tolerates varies by sequence, so this is general handling guidance, not a guarantee for your compound. These are research-use materials. Anything involving injection or dosing is a question for a licensed provider.