Store sealed freeze-dried peptide powder in the refrigerator at 2–8°C (a freezer for long gaps), and keep any mixed vial refrigerated, out of light, and never refrozen. An opened multi-dose vial is conventionally discarded within 28 days, sooner if the pharmacy label says so. Branded GLP-1 pens allow 21 to 56 days at room temperature.[7]
How a peptide is stored decides whether the molecule you draw up months from now is the same molecule you paid for. Peptides are chains of amino acids held together by bonds that water, heat, light, and time can all break. The single most important variable is the physical form: a dry, freeze-dried powder behaves very differently from the same peptide once it is dissolved in liquid. This guide covers storage and stability only. If you need the mixing steps themselves, see our companion guide on how to reconstitute peptides; here we pick up the moment the vial arrives and follow it through to the point you discard it.
Lyophilized powder versus reconstituted solution
Most research peptides ship as a lyophilized (freeze-dried) powder. Removing water dramatically slows the chemical reactions that degrade a peptide, which is why dry formulations can remain stable for long periods when kept cold and sealed.[1] The trade-off arrives the instant you add diluent: in solution, hydrolysis, oxidation, and aggregation all accelerate, and shelf life collapses from months or years down to weeks. A study of lyophilized PTH(1-34), a 34-residue peptide closely comparable to the research peptides sold today, found the dry material far more durable than the same peptide once reconstituted, with measurable loss beginning soon after mixing.[2] Treat the two forms as two different products with two different clocks.
What temperature should peptides be stored at?
For sealed lyophilized powder, refrigeration at 2–8°C (the standard pharmacy “refrigerated” range) is the everyday baseline, and a freezer extends the practical window further for vials you will not touch for weeks. Cold storage is what keeps the slow, residual degradation of a dry formulation slow.[1] Once reconstituted, the working rule is simple: refrigerate at 2–8°C and use within the dated window. Approved peptide drugs show how product-specific these rules are. The U.S. prescribing information for tesamorelin (Egrifta SV) has the dry 2 mg vials kept at room temperature, 20–25°C, away from light, but once mixed the solution must be injected right away and never stored, refrigerated or frozen.[3] The dry powder tolerates room temperature because the manufacturer tested that exact formulation; the dissolved peptide does not sit at all. A research peptide with no such testing has no proven room-temperature allowance, so cold storage is the conservative default.
The enemies of stability
Heat speeds every degradation reaction; leaving a vial in a warm car or near a window undoes the protection of cold storage. Light is a quieter threat: ultraviolet and even visible light drive oxidation, and light-induced oxidation of residues such as tryptophan can fragment the peptide backbone and create breakdown products that simply are not the molecule you intended to use.[4] Keep vials in their box or otherwise shielded from light. Repeated freeze–thaw is especially damaging to a peptide in solution; each cycle concentrates solutes and stresses the molecule, promoting aggregation, so a reconstituted vial should never be frozen and thawed repeatedly.[5] Agitation — shaking or rough transit — introduces air–liquid interfaces that encourage the same aggregation, which is one reason reconstitution calls for gentle swirling rather than vigorous shaking.
Bacteriostatic versus sterile water
The diluent you choose is also a storage decision. Sterile water contains no preservative, so a vial reconstituted with it should be treated as single-use or used very quickly. Bacteriostatic water contains roughly 0.9% benzyl alcohol, a preservative that suppresses microbial growth and is the reason a multi-dose vial can be entered repeatedly; CDC guidance, based on USP <797>, is to date an opened multi-dose vial and discard it within 28 days unless the manufacturer states otherwise.[7] Benzyl alcohol is not free, however: it can interact with some peptides and proteins and, in certain formulations, has been shown to promote aggregation.[6] The practical takeaway is to match diluent to use — bacteriostatic water for a vial you will draw from repeatedly, sterile water only when you intend to use the contents at once — and to remember that “preserved” protects against microbes, not against chemical degradation of the peptide itself. (Our companion guide on bacteriostatic water for peptides covers the preservative and its in-use shelf life in more detail.)
How long do compounded semaglutide and tirzepatide last in the fridge?
As long as the beyond-use date the compounding pharmacy prints on the vial, and no longer. A compounded GLP-1 has no FDA label, so there is no standard shelf life: the pharmacy sets the date from its own sterility and stability testing, and dates differ from one pharmacy to the next. Keep it at 2–8°C and follow that label. How many doses a tirzepatide vial holds at each step is worked out in our compounded tirzepatide dosage chart.
The branded versions show how carefully these limits are drawn, and why one product's figure does not transfer to another. All of them are refrigerated until first use and must never be frozen.
Swipe to see all columns
| Branded product | In the refrigerator (2–8°C) | Out of the refrigerator |
|---|---|---|
| Wegovy single-dose pen | Until the expiration date | Up to 28 days at 8–30°C, before the cap is removed |
| Ozempic pen (and Wegovy FlexTouch) | Until the expiration date, before first use | After first use, 56 days at 15–30°C or in the refrigerator |
| Zepbound or Mounjaro single-dose pen or vial | Until the expiration date | Up to a total of 21 days at or below 30°C |
| Zepbound or Mounjaro KwikPen or multi-dose vial | Unopened: until the expiration date | Discard 30 days after first use or after 4 weekly doses, whichever comes first; unopened, 30 days at room temperature |
If a compounded vial has no beyond-use date on it, ask the pharmacy before you use it. For what the drugs cost by route, see our Wegovy cost and tirzepatide cost guides.[8][9][10][11]
Practical handling
Label every reconstituted vial with the date and concentration the moment you mix it; memory is not a stability strategy, and the date is what tells you when to stop using it. Return vials to the refrigerator promptly rather than leaving them on the counter between doses, and minimize the time spent at room temperature. For travel, a small insulated cooler with a cold pack keeps powder and solution in range, but avoid direct contact with ice, which can locally freeze and stress a reconstituted solution. When shipping or receiving, expect that cold-chain handling matters: lyophilized powder tolerates brief excursions far better than liquid, which is another reason most peptides ship dry.
How can you tell if a peptide has gone bad?
Inspect every vial before use. A properly reconstituted peptide solution should be clear and colorless. Cloudiness, haze, visible particulates, floating flakes, or any color change are signs of aggregation, contamination, or breakdown, and the vial should be discarded rather than injected. Likewise discard anything past its labeled date, anything that was left warm for an extended period, or any reconstituted vial whose history you are unsure of. Degraded peptide is not just weaker; the breakdown products are unknown quantities.
The honest bottom line
Keep powder cold and dark, reconstitute only what you will use within 28 days or the label date, refrigerate the solution, protect it from heat, light, freeze–thaw, and rough handling, label it with a date, and discard anything cloudy or expired. Most research peptides are not FDA-approved and carry no validated stability data of their own, so cold, dark, dated storage is the most defensible standard to follow; approved labels show that any room-temperature allowance has to be proven for that exact product.[3] This is general handling information, not medical or dosing advice.
