One of the most common questions in peptide research is simply: how long does it keep? The answer has two parts, because a peptide has two very different lifespans — one before you mix it, and one after. Here's the plain-English version.
The short answer
- Lyophilised (freeze-dried) powder, unopened: stable for a long time — typically many months to a couple of years when kept cold and sealed.
- Reconstituted (mixed with liquid), in the fridge: a much shorter window — generally on the order of a few weeks, depending on the peptide and conditions.
In other words: the dry powder is the durable form; once it's in solution, the clock speeds up.
Why lyophilised powder lasts so long
Freeze-drying removes the water, and water is what most degradation reactions need. With the moisture gone and the vial kept cold and sealed, a lyophilised peptide is in its most stable state. That's why peptides are shipped and stored as powder, not pre-mixed — it's the format that survives transit and storage. Keep unopened vials at −20°C where possible.
Why reconstituted peptides have a shorter life
Once you add bacteriostatic water, two things start working against stability: the peptide is now in solution (so those water-dependent reactions can proceed), and the vial gets opened and handled. Bacteriostatic water contains a preservative that suppresses microbial growth, which is exactly why it's preferred over plain sterile water for multi-use vials — but it doesn't stop chemical degradation forever. Keep reconstituted vials refrigerated (2–8°C), not frozen, and away from light.
The factors that actually move the needle
- Temperature — the single biggest factor. Cold slows everything down; heat and freeze-thaw cycles speed degradation up.
- Light — many peptides are light-sensitive; keep vials in the dark.
- Water type — bacteriostatic (preserved) water for multi-use vials; plain sterile water has no preservative.
- Handling — repeated opening, warming to room temperature, and freeze-thaw cycles all shorten the window.
- The peptide itself — some sequences are inherently more stable than others.
Practical takeaways
Buy as powder, store cold, and only reconstitute what you'll use within a reasonable window. Our guide to storing and reconstituting peptides covers the how-to, and the reconstitution calculator helps you mix the right amount so you're not left with solution sitting past its best.
Sourcing fresh, tested peptides
Stability starts with what you begin with. Everything we stock is independently batch-tested for purity and identity, with a published Certificate of Analysis you can check in our CoA Library — dispatched same or next business day from Melbourne so it reaches you fresh.
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All products are supplied strictly for laboratory and in-vitro research use only. Not for human or veterinary consumption. This article describes general handling of research materials and is not medical advice.