Storing peptides: what each kind of source says

There is no single storage answer

“How should I store peptides?” hides a different question per compound and per state: a lyophilized solid and a reconstituted solution are different materials with different chemistry, and an FDA-approved product's label states storage conditions that were established for that exact formulation. This guide separates the sources instead of pretending they agree.

Lyophilized (powder)

The research-literature convention for lyophilized peptides is cold and dry: freezer temperatures (commonly cited around −20 °C) for longer-term storage, refrigeration for shorter intervals, protected from light, in airtight containers. The reason is the degradation chemistry from the first guide in this series — water, oxygen and light each drive specific degradation pathways, and cold slows all of them.

Manufacturer/supplier claims commonly extend further — “stable at room temperature for shipping”, multi-year shelf lives — and are exactly that: claims by the party selling the material. The verifiable version of a shelf life is a stability study, and few suppliers publish one.

Reconstituted (in solution)

In solution, degradation accelerates dramatically. The literature convention is refrigeration, short windows, and often a stated instruction against freezing solutions — freeze/thaw cycling mechanically stresses dissolved peptides and can promote aggregation. How short the window is depends on the sequence, the diluent, the concentration and sterility; the widely circulated community convention of “about 4 weeks refrigerated” for bacteriostatic-diluent solutions is a convention, not a study.

Community practice is itself a source worth reporting: people commonly refrigerate reconstituted vials for weeks and describe using them beyond conventional windows. Therapept reports that practice where relevant — labelled as community practice — because it is a real description of the sector, not because it is equivalent to stability data.

FDA-approved products

Approved peptide drugs carry label-stated storage conditions established for their exact formulation — pens, vials, pre-filled syringes each with specifics. The Victoza label, for example, instructs storage in a refrigerator before first use, with defined in-use periods and temperatures for the pen in use. Those statements are specific to that product's formulation and container and do not transfer to research materials. The dosing reference links each approved compound's label; the label's storage section is the authoritative source for that product.

Research-literature conditions

Papers describing peptide work typically state handling in methods sections: aliquoted stock solutions stored frozen, avoid repeated freeze/thaw, protect from light. These are laboratory conventions for analytical work — they describe how researchers preserve measurement fidelity, which is a different goal from maintaining a multi-use vial.

What changes between compounds

Sequence chemistry guarantees variation: oxidation-prone residues (methionine, cysteine, tryptophan), aggregation-prone stretches, and acid-labile bonds all make some peptides materially fussier than others. Where compound-specific stability data exists, it is linked from that compound's identity page. Where it does not, no guide — including this one — can honestly fill the gap.