How long do lyophilized peptides last?

GenScript says most lyophilized peptides are stable for several years at −20 °C away from bright light; JPT says peptides stored dry, sealed, desiccated and dark at −20 °C to −80 °C can remain stable for years, with periodic stability testing recommended. Both guides note that some sequences are exceptions: peptides with cysteine, methionine or tryptophan oxidise, and peptides rich in charged residues absorb moisture, which shortens the shelf-life of the powder itself.

Do peptides need to be refrigerated or frozen?

The manufacturers' guides say frozen, for the dry powder: −20 °C at GenScript, −20 °C to −80 °C at JPT, with lower temperatures preferred for long-term storage. Refrigeration at 2 to 8 °C is not the condition either guide specifies for long-term storage of lyophilized peptide. For solutions, the guidance is −20 °C or lower in single-use aliquots, or not to store solutions at all.

How long does a reconstituted peptide last?

The manufacturers' guides do not give a number for the case people usually mean, a peptide dissolved in bacteriostatic water and kept in a refrigerator. GenScript says the shelf-life of peptides in solution is very limited and much shorter than lyophilized, recommends against storing solutions, and, where unavoidable, recommends a pH 5 to 6 buffer in aliquots at −20 °C. JPT says reconstituted peptides go to −20 °C or lower and should be aliquoted to avoid freeze-thaw. Any specific number of days at 4 °C on a vendor page is that vendor's claim, not the manufacturers' guidance we could find.

Can peptides be frozen and thawed more than once?

The guides advise against it. GenScript: peptides that undergo freeze-thaw cycles are susceptible to degradation, so the amount needed should be pre-determined and aliquoted. JPT: repeated freeze-thaw cycles cause degradation through microcondensation, and single-use aliquots avoid repeated exposure. The practical consequence is that a solution is divided once, not thawed repeatedly.

Does light damage peptides?

GenScript specifies storage away from bright light; JPT specifies dark conditions or amber vials to prevent photodegradation. Tryptophan, methionine and cysteine are the residues most affected by oxidation, which light accelerates.

How is bacteriostatic water stored?

The Hospira label says 20 to 25 °C (68 to 77 °F), USP controlled room temperature, with no refrigeration instruction. For an opened vial, CDC's injection-safety guidance sets a discard date, within 28 days unless the manufacturer states another, and the Hospira label states none. Our bacteriostatic-water guide covers the label in full.

How Research Peptides Are Stored: What the Manufacturers' Guides and the Labels Say

Lyophilized versus reconstituted, freezer versus fridge, light, moisture, freeze-thaw and which amino acids degrade first, taken from peptide manufacturers' own handling guides, the Hospira bacteriostatic-water label and CDC's multi-dose-vial rule.

Peptide storage advice on vendor pages is confident and unsourced: a number of days in the refrigerator, a number of months in the freezer, presented as fact. The people who actually specify storage conditions are the manufacturers who synthesize peptides for laboratories, and their handling guides are public. This page reports what two of them say, what the bacteriostatic-water label says, and what CDC says about opened vials, and it is explicit about the one question none of those sources answers. It does not tell any laboratory what to do; it reports what the documents say.

Rankings on Peptifact follow the published criteria and are never sold; how brands appear on this site is set out on our disclosure page.

The two states of a peptide

A research peptide arrives lyophilized: freeze-dried to a powder in a sealed vial. At some point it is reconstituted, dissolved in a liquid. The manufacturers' guides treat these as different substances for storage purposes, and the difference is the whole subject.

Lyophilized: what the guides say

Temperature. GenScript: "Lyophilized peptides should be stored at −20 °C, away from bright light. Most lyophilized peptides are stable for several years under these conditions." JPT: "Dry peptides should be stored at −20 °C to −80 °C", with lower temperatures preferred for long-term storage; "peptides stored under these conditions can remain stable for years, although periodic stability testing is recommended." (GenScript; JPT)

Moisture. JPT: "Peptides should be stored in a tightly sealed, desiccated container. Vacuum-sealed or nitrogen-flushed containers are ideal to prevent moisture ingress." GenScript names the sequences that matter most: "Peptides containing Asp, Glu, Lys, Arg, or His are prone to moisture absorption from the air, called deliquescence. These peptides should be stored in a desiccator in a tightly capped vial." A vial taken from a freezer and opened cold condenses water onto the powder, which is why both guides, in effect, say to let a vial reach room temperature before opening it.

Light. GenScript: "away from bright light." JPT: "dark conditions or in amber-colored vials to prevent photodegradation."

Oxidation. GenScript: "Peptides containing Cys, Met, or Trp residues are prone to oxidation and require storage under anaerobic conditions to maintain stability." JPT names "methionine, cysteine, tryptophan, and asparagine" as "more prone to oxidation and hydrolysis."

None of this depends on what the peptide is for. It depends on the sequence, which is printed on the certificate of analysis.

Reconstituted: what the guides say, and what they do not

GenScript: "The shelf-life of peptides in solution is very limited, much shorter than that of lyophilized peptides", particularly for sequences containing Cys, Met, Trp, Asp, Gln or N-terminal Glu, and the company "does not recommend storing peptides in solution." Where storage is unavoidable: "use buffers at pH 5–6 to dissolve your peptide, divide the peptide solution into aliquots, and store the aliquots at −20 °C. Avoid freeze-thaw cycles of the aliquots." JPT: "Reconstituted peptides should be stored at −20 °C or lower, depending on their stability in solution", and "repeated freeze-thaw cycles can still cause degradation through microcondensation. It is advisable to aliquot peptides into single-use vials."

Now the gap. The question most people bring to this page is how long a peptide lasts once dissolved in bacteriostatic water and kept in a refrigerator. Neither guide answers it. Neither gives a number of days at 2 to 8 °C; both point to −20 °C aliquots or to not storing solutions at all. Bacteriostatic water's preservative, 0.9% benzyl alcohol, inhibits bacterial growth in the vial; it does nothing about the chemistry that degrades a peptide in solution, which is oxidation, hydrolysis and aggregation, all of which run faster at refrigerator temperature than in a freezer. The "28 days" figure that vendor pages attach to reconstituted peptides is CDC's rule for the opened multi-dose vial of diluent, not a stability figure for any peptide. We looked for a manufacturer's guide that states a refrigerated shelf-life for a peptide in bacteriostatic water and did not find one; a page that gives one should say where it comes from.

The diluent's own label

Bacteriostatic Water for Injection, USP (Hospira, NDC 0409-3977-01) is stored at 20 to 25 °C, USP controlled room temperature; the label gives no refrigeration instruction and no discard date for an opened vial. CDC's injection-safety guidance, dated 2024-03-26, says: "Once a multi-dose vial is opened (e.g., needle-punctured) the vial should be dated and discarded within 28 days unless the manufacturer states another date for that opened vial." The label, the NDC records and the vendor prices are in our bacteriostatic-water guide.

A storage table, from the sources

State	Temperature	Container	Light	Handling	Source
Lyophilized, long term	−20 °C (GenScript); −20 °C to −80 °C, lower preferred (JPT)	Tightly sealed, desiccated; vacuum or nitrogen-flushed ideal	Dark or amber vial	Warm to room temperature before opening; desiccator for Asp/Glu/Lys/Arg/His-rich sequences; anaerobic for Cys/Met/Trp	GenScript, JPT
Reconstituted, if stored at all	−20 °C or lower	Single-use aliquots	Dark	pH 5 to 6 buffer (GenScript); no repeated freeze-thaw	GenScript, JPT
Reconstituted in bacteriostatic water, refrigerated	Not specified by either guide	Not specified	Not specified	No manufacturer figure found	This page
Bacteriostatic water, unopened	20 to 25 °C	Original vial	Not specified	Do not refrigerate per label (no instruction to)	Hospira label
Bacteriostatic water, opened	20 to 25 °C	Original vial, dated	Not specified	Discard within 28 days unless manufacturer states another date	CDC

What this page does not do

It does not say how to reconstitute a peptide, at what concentration, or what to do with the solution. It reports storage conditions published by manufacturers and regulators and links each one. Where the sources are silent, it says so rather than filling the gap.

Sources and dates

Opened 2026-09-05: GenScript's Peptide Storage and Handling Guidelines; JPT's How to Store Peptides; the Hospira Bacteriostatic Water for Injection label on DailyMed (as reported in our bacteriostatic-water guide); CDC's injection-safety guidance (2024-03-26). Biosynth's and Tocris's storage pages could not be opened on the day and are not quoted. Corrections and additional manufacturer guidance go to the contact page; who we are is on the about page.