How long does a reconstituted peptide last?

Stability varies by peptide and by handling. A common working guideline is 14–30 days refrigerated once reconstituted with bacteriostatic water, but that is a rule of thumb, not a property of every compound.

What actually drives the window

• The diluent. Bacteriostatic water contains ~0.9% benzyl alcohol, which suppresses bacterial growth and is why it supports multi-day use. Sterile water has no preservative and is generally treated as single-use.
• Temperature. Refrigeration slows both chemical degradation and microbial growth. Repeated warming and cooling is worse than steady cold.
• Freeze–thaw cycles. Each cycle stresses the peptide. Freezing an already-reconstituted vial is usually avoided for this reason.
• Light and agitation. Both accelerate degradation; shaking in particular denatures peptides at the air–liquid interface.
• The peptide itself. Sequence, molecular weight and any stabilising modification all change the answer. A PEGylated or albumin-binding analog behaves differently from an unmodified fragment.

Lyophilised powder is far more stable than solution, which is why compounds ship dry and are reconstituted only when needed. If a vendor publishes stability data for a specific compound, that data beats any general guideline.

See also how reconstituted peptides should be stored and why peptides degrade faster after reconstitution. Research use only. Not medical advice.