Peptide Storage
How to Store Peptides: Lyophilized Powder vs Reconstituted Solution
Dry peptide powder: cold, dry, dark and sealed — 4°C or colder for working storage, -20°C for the long term, and warmed to room temperature before the vial is opened. A reconstituted peptide is a different question with no universal answer: two FDA labels for the same peptide give different rules, and both of them forbid the refrigerator. This page sets the reference guidance beside the labels. Research-material handling education only.
The short answer
- Lyophilized, working storage: 4°C (39°F) or colder, away from bright light (NIBSC).
- Lyophilized, long term: -20°C (-4°F) — the preferred condition in both reference documents checked, and one at which GenScript describes most lyophilized peptides as stable for several years.
- Moisture is the quiet enemy: seal tightly, and let a cold vial reach room temperature before opening it.
- Reconstituted, labeled product: follow that label exactly. Labels range from “discard if not used immediately” to 28 days, and from 2–8°C to “do not refrigerate.”
- Reconstituted, unlabeled research material: reference guidance does not recommend solution storage; where it cannot be avoided, sterile buffer near pH 5–6, single-use aliquots, -20°C or colder, no repeated freeze-thaw.
What the reference guidance says
Two handling documents written for unlabeled research peptides: the peptide-storage guidance published by NIBSC, the UK National Institute for Biological Standards and Control, and GenScript’s storage and handling guidelines. Quotation marks mean the words are theirs. They agree on every point where both speak.
| Situation | Guidance | Source |
|---|---|---|
| Dry powder, working storage | “store at 4°C or colder away from bright light” | NIBSC |
| Dry powder, long term | “For long-term storage -20°C is to be preferred” | NIBSC; GenScript (-20 °C) |
| Dry powder at room temperature | “Dry peptides are stable at room temperature for days to weeks” | NIBSC |
| Before opening a cold vial | Allow it to warm to room temperature first | NIBSC; GenScript |
| After opening | Re-seal, “preferably under an atmosphere of dry inert gas” | NIBSC |
| Solution, if unavoidable | Sterile buffer around pH 5–6, aliquots at -20 °C or colder | NIBSC; GenScript |
| Freeze-thaw | “Repeated freeze-thaw cycles are deleterious to peptides” | NIBSC |
| Freezer type | “Avoid the use of frost-free freezers” | NIBSC |
Why a dissolved peptide degrades so much faster
In the dry state the reactions that break a peptide down have almost no water to run in. Dissolve it and they start, at a rate set by the sequence. That is why no honest page can give one shelf-life figure for “peptides”: the number belongs to a molecule, a solvent, a pH and a temperature together.
| Residues | Vulnerability | What the guidance says |
|---|---|---|
| Cys, Met, Trp | Oxidation | GenScript: prone to oxidation; store without air where possible |
| Asn, Gln | Deamidation — limits solution shelf life | NIBSC names C, M, N, Q and W for solutions |
| Asp, Glu, Lys, Arg, His | Moisture uptake from air (deliquescence) | GenScript: keep in a desiccator, tightly capped |
How large the sequence effect is has been measured. Geiger and Clarke found that the model hexapeptide VYPNGA deamidates with a half-life of 1.4 days at 37°C and pH 7.4 — at that rate about 3% would remain intact after a week — while replacing the glycine after the asparagine with leucine or proline slowed degradation 33- to 50-fold (J Biol Chem 1987;262(2):785–794; PMID 3805008). One residue changed, and the stable life of the molecule changed by more than an order of magnitude. Those are body temperature and neutral pH, not a refrigerator, and they describe a model peptide rather than any product; the point they make is that a single figure cannot cover every sequence.
What the labels of reconstituted peptides actually say
The rule repeated online is “refrigerate after mixing and use within 28 days.” Printed labeling does not support a rule. The clearest evidence is a single peptide sold in two formulations: tesamorelin as EGRIFTA SV and as EGRIFTA WR, both from Theratechnologies. Mixed with Sterile Water, the SV label says to discard the solution if it is not used immediately and “Do not store, freeze or refrigerate” it. Mixed with Bacteriostatic Water, the WR label directs room temperature, 20 to 25°C, discard 7 days after mixing, and “Do not freeze or refrigerate.” Same molecule; two storage regimes; neither of them a fridge.
| Reconstituted product | Stated temperature | Stated window | Source |
|---|---|---|---|
| Tesamorelin (EGRIFTA SV), mixed with Sterile Water | Do not store, freeze or refrigerate | Discard if not used immediately | EGRIFTA SV labeling |
| Somatropin (GENOTROPIN MINIQUICK), preservative-free | 2–8 °C | Up to 24 hours after mixing | GENOTROPIN MINIQUICK labeling |
| Tesamorelin (EGRIFTA WR), mixed with Bacteriostatic Water | 20–25 °C — “Do not freeze or refrigerate” | Discard 7 days after mixing | EGRIFTA WR labeling |
| Somatropin (GENOTROPIN), metacresol-preserved | 2–8 °C | Up to 28 days | GENOTROPIN labeling |
| Teriparatide (FORTEO) pen solution | 2–8 °C except while administering | 28 days after first use | FORTEO labeling |
These are approved medicines whose labels describe their own formulations; they are cited because they are the only documents that state a reconstituted peptide’s storage outright, not as a guide to any other material. What they establish is negative and useful: the refrigerator and the 28 days are properties of particular products, not of peptides.
Where the “28 days” comes from
It comes from the container, not the peptide. USP <797> Section 15.2 says a punctured multiple-dose container “is not used for more than 28 days unless otherwise specified by the manufacturer on the labeling,” and CDC says an opened multi-dose vial should be dated and discarded within 28 days unless the manufacturer states another date. That limit exists because repeated needle entry can introduce microbes; the preservative in bacteriostatic water is what makes 28 days defensible for the water. It says nothing about how quickly a peptide dissolved in that water deamidates or oxidises.
The EGRIFTA WR label prints the two clocks side by side, which is as clean a demonstration as exists: the Bacteriostatic Water bottle is discarded 28 days after first use; the peptide vial reconstituted with that same water is discarded 7 days after mixing. The water’s own storage condition is room temperature too — covered on the bacteriostatic water storage page.
Fridge or freezer?
Dry powder: the freezer is the long-term answer and the refrigerator the working one. Two cautions from NIBSC change how a freezer is used rather than whether: avoid frost-free models, whose defrost cycle warms the contents repeatedly, and do not keep taking the same vial in and out — every cold vial opened before it has warmed takes on water.
Solution: freezing is where the most damage is done by habit. Reference guidance freezes solutions only as single-use aliquots, precisely so that no portion is thawed twice. For labeled products, the question is already answered, and the answer can be no: both EGRIFTA labels prohibit freezing the mixed solution.
Left out, or delivered warm
For dry powder the reference position is reassuring: NIBSC states that dry peptides are stable at room temperature for days to weeks, which covers an ordinary shipment. Mail transit is not gentle — Chowdhury and colleagues logged packages spending an average of 68.3% of transit time outside 68–77°F, with extremes of 5.1°F and 102.3°F (J Am Pharm Assoc 2023;63(3):847–852; PMID 36858884) — but that measured oral medicines in simulated transit, not peptides, and is evidence about the journey rather than about any product. A solution left out is a different matter, and without a label there is no published figure that would make a confident answer honest.
Common storage mistakes
- Opening a vial straight from the freezer. Condensation lands on the powder; let the sealed vial warm first.
- Treating 28 days as the peptide’s shelf life. It is the water container’s in-use limit.
- Refrigerating every mixed vial by reflex. Both tesamorelin labels cited above prohibit refrigerating the mixed solution.
- Thawing the same solution repeatedly. Freeze single-use aliquots or do not freeze.
- Using a frost-free freezer for long-term storage. Its defrost cycle is a slow freeze-thaw.
- Storing the water like the peptide. Bacteriostatic water is labeled for controlled room temperature.
What Medibact supplies
Medibact stocks USP-grade bacteriostatic water produced in an FDA-registered U.S. facility, sold for research use only. Medibact does not sell the labeled products named on this page and is not affiliated with Theratechnologies, Pfizer, Eli Lilly, GenScript or NIBSC; their documents are cited because they answer the storage question, and nothing here describes how any product should be used.
Where this sits in the rest of the reference
FAQ
How should peptides be stored?
It depends on the state the peptide is in. As a dry (lyophilized) powder: cold, dry, dark and sealed — NIBSC gives “4°C or colder away from bright light” and states that “for long-term storage -20°C is to be preferred.” As a solution: for a labeled product, exactly as its label says, because labels for the same peptide disagree; for unlabeled research material, reference guidance treats solution storage as a last resort — sterile buffer around pH 5–6, aliquots, -20 °C or colder, no repeated freeze-thaw.
Do peptides need to be refrigerated?
Dry peptide powder is better kept cold, and a freezer is the preferred long-term condition in both reference documents checked. A reconstituted peptide has no single answer: the GENOTROPIN and FORTEO labels direct 2–8 °C, while the EGRIFTA WR label directs 20–25 °C and says “Do not freeze or refrigerate” once mixed. The formulation decides, not the word “peptide.”
How long do reconstituted peptides last?
There is no general figure, and the labeled ones run from “immediately” to four weeks: EGRIFTA SV is discarded “if not used immediately,” GENOTROPIN MINIQUICK allows up to 24 hours at 2–8 °C, EGRIFTA WR 7 days at room temperature, GENOTROPIN and FORTEO up to 28 days at 2–8 °C. For unlabeled material, GenScript states that shelf life in solution is “very limited, much shorter than that of lyophilized peptides” and recommends not storing peptides in solution at all.
Does mixing with bacteriostatic water make a peptide last 28 days?
No. Twenty-eight days is the in-use limit for the punctured water container under USP <797> §15.2 — a statement about microbial risk in a multiple-dose container, not about the peptide’s chemical stability. The EGRIFTA WR label shows the two clocks side by side: the bacteriostatic water bottle is discarded 28 days after first use, the peptide vial mixed with that same water 7 days after mixing.
Can peptides be frozen?
Dry powder, yes — -20 °C is the reference long-term condition. Solutions are where freezing goes wrong: NIBSC calls repeated freeze-thaw cycles “deleterious to peptides” and advises against frost-free freezers, which cycle their temperature. Reference guidance freezes solutions only as single-use aliquots. Labeled products can prohibit it outright — both EGRIFTA labels say not to freeze the mixed solution.
What happens if peptides are left out of the fridge?
For dry powder, a short excursion is usually not a loss: NIBSC states that dry peptides “are stable at room temperature for days to weeks.” For a solution, the answer is the label’s, where there is one — some labeled peptide solutions are meant to sit at room temperature, others are not. For unlabeled solutions no published figure exists that would make a confident answer honest.
Why should a cold vial warm up before it is opened?
Because a cold powder pulls moisture out of room air the moment the vial is opened, and NIBSC states that “contamination with moisture will greatly decrease long term stability.” Both NIBSC and GenScript direct letting the sealed vial reach room temperature first. Peptides rich in Asp, Glu, Lys, Arg or His absorb water most readily, per GenScript.
Do peptides expire?
Yes, and a labeled product states its date. Unlabeled lyophilized research material has no universal expiry — GenScript describes most lyophilized peptides as stable for several years at -20 °C away from bright light — while any solution is on a far shorter and sequence-dependent clock.
Is this medical advice?
No. This page is research-material handling education drawn from reference documents and published labeling. It is not medical advice and contains no dosing, route or frequency instruction. Product labels are cited because they answer the storage question; Medibact is not affiliated with Theratechnologies, Pfizer, Eli Lilly or any manufacturer named here.
Educational use only — not medical advice. This guide summarizes information reported in published research and community practice for educational purposes. It is not medical advice and not a recommendation to use any compound. Any doses, schedules, or combinations shown are examples of what has been reported, not instructions for you. Many peptides described here are research compounds that are not FDA-approved for the uses discussed and may be investigational or restricted. Effects, risks, and legal status vary; individual needs and results vary. Consult a qualified, licensed healthcare professional before making any decision. Do not use this content to diagnose, treat, or dose yourself.