Storage

The short version

• An approved product: store it exactly as its label says. Labels differ more than people expect (examples below).
• Dry powder keeps better than liquid. Once a peptide is in water, both chemical breakdown and the risk of bacterial growth start counting.
• Mixed solution: refrigerate, protect from light, never freeze, date the vial.
• Two separate clocks run on a mixed vial: sterility (has anything started growing in it?) and stability (is the peptide still intact?). Neither can be checked by looking.
• When in doubt, discard.

What the temperature words mean

Pharmacy standards define storage terms precisely. These are the definitions in USP General Chapter <659> [1]:

A kitchen fridge is not a pharmacy fridge. A cheap fridge thermometer tells you whether yours actually holds 2–8 °C. The door shelf is the warmest and least steady spot, and anything touching the back wall or sitting under the freezer plate can freeze.

Dry (lyophilised) powder versus mixed solution

Freeze-drying removes the water from a peptide. Most of the reactions that break peptides down need water, so a dry powder in a sealed vial is far more stable than the same peptide in solution [2][3].

In water, peptides degrade by several routes at once: hydrolysis (the chain is cut), deamidation and oxidation (individual amino acids change), and aggregation (molecules clump together, sometimes into visible particles). Higher temperature, the wrong pH, light, dissolved oxygen, and shaking all speed these up [2][3][4]. Aggregates are not just lost dose: clumped peptide is one of the reasons regulators worry about immune reactions to poorly made or poorly stored products [5].

Mixing also adds a second risk that has nothing to do with chemistry: every time a needle goes through the stopper, bacteria can get in. The review literature notes plainly that reconstitution "poses a risk of contamination" [2].

Fridge or freezer?

Dry powder

• Approved product: follow the label. Some lyophilised peptides are labelled for room temperature, not the fridge. Tesamorelin vials, for example, are stored at 20–25 °C in the original box [6][7].
• No label to follow: colder and drier slows degradation, so sealed dry vials are generally kept in a refrigerator or freezer, in the dark. There is no validated expiry for an unapproved product, whatever its packaging says.
• Let a cold vial warm up before opening or puncturing it, so moisture from the room does not condense on it.

Mixed (reconstituted) solution

• Refrigerator, 2–8 °C, unless a product label says otherwise.
• Do not freeze it. Labels for injectable peptide solutions say this consistently, and say to discard a product that has been frozen [6][8][9][10]. Freezing and thawing is a recognised stress that can make peptides aggregate [2].
• Tesamorelin shows why the label matters: one formulation, mixed with preserved water, is kept at room temperature and used for 7 days; the other, mixed with plain sterile water, must be injected immediately and any remainder thrown away, and is not to be refrigerated or frozen [6][7].

Light

Light drives oxidation of several amino acids (tryptophan, tyrosine, phenylalanine) and of disulfide bonds [2]. That is why labels say to keep vials and pens in the original carton [8][9][10]. Keep vials boxed or wrapped, and never on a windowsill or in a car.

Temperature excursions

An excursion is time spent outside the intended range: a delayed parcel, a power cut, a vial left on the counter.

For approved products, the label states what is tolerated, because the manufacturer tested it:

For anything without tested data, there is no allowance to rely on. A conservative rule set:

• Mixed solution that has frozen: discard.
• Mixed solution that got hot (a parked car, direct sun, above about 30 °C) or was out of the fridge for an unknown length of time: discard.
• Dry powder that got hot, or arrived warm after days in transit: it may look unchanged and still be degraded. You cannot test it at home. Discarding is the only way to be sure.
• A brief, known excursion (minutes on the counter while preparing a dose) is expected and unavoidable. Put the vial straight back.

How long is a mixed vial usable?

There are two different limits, and the shorter one applies.

1. Sterility. Professional standards for sterile preparation (USP <797>) set time limits by how and where a product was prepared, because sterility cannot be seen [12][13]:

• A multiple-dose vial that contains an antimicrobial preservative may be used for up to 28 days after the first puncture, unless the manufacturer says otherwise [12][13][14]. The preservative is what makes this possible, and the 28-day figure assumes a manufactured product whose preservative was tested.
• A single-dose vial has no preservative. Opened outside a sterile compounding environment, it is for one use only, with no storage of what is left [13][14]. A preparation made outside such an environment is treated as "immediate use": to be given within about 4 hours [13].

Applied to home mixing: a vial mixed with bacteriostatic water (water with 0.9% benzyl alcohol as a preservative, sold as a multiple-dose diluent) [15] is conventionally treated as usable for up to about four weeks in the fridge. A vial mixed with plain sterile water has no preservative and should be treated as single use. A kitchen is not a clean room, so 28 days is an upper bound borrowed from better conditions, not a promise.

2. Stability. The 28-day convention is about bacteria only. It says nothing about whether a given peptide survives that long in solution [13]. Some do not: the preserved tesamorelin formulation is labelled for just 7 days [6]. For unapproved peptides there is usually no published in-use stability data at all.

Practical consequences:

• Write the mixing date and the discard date on the vial when you mix it.
• Use the product's labelled in-use period if it has one.
• If it has none, do not go beyond 28 days for a preserved solution, and shorter is safer.
• Unpreserved solution: one use.
• Discard earlier at any sign from the warning signs checklist, or whenever sterility is "compromised or questionable", in the words of the CDC [14].

Sources

Checked 13 November 2026.

1. United States Pharmacopeia. General Chapter <659> "Packaging and Storage Requirements." USP–NF. https://doi.org/10.31003/USPNF_M2773_06_01
2. Nugrahadi PP, Hinrichs WLJ, Frijlink HW, Schöneich C, Avanti C. "Designing Formulation Strategies for Enhanced Stability of Therapeutic Peptides in Aqueous Solutions: A Review." Pharmaceutics. 2023;15(3):935. https://doi.org/10.3390/pharmaceutics15030935
3. Manning MC, Chou DK, Murphy BM, Payne RW, Katayama DS. "Stability of protein pharmaceuticals: an update." Pharmaceutical Research. 2010;27(4):544–575. https://doi.org/10.1007/s11095-009-0045-6
4. Zapadka KL, Becher FJ, Gomes dos Santos AL, Jackson SE. "Factors affecting the physical stability (aggregation) of peptide therapeutics." Interface Focus. 2017;7(6):20170030. https://doi.org/10.1098/rsfs.2017.0030
5. U.S. Food and Drug Administration. "Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks." https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks
6. Tesamorelin for injection (Egrifta WR), US prescribing information and instructions for use, DailyMed. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=839334d3-8c1d-4c26-9036-2ab524a6ea75
7. Tesamorelin for injection (Egrifta SV), US prescribing information, DailyMed. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=3d783378-b02d-4f19-99dd-0fc91a042224
8. Tirzepatide (Zepbound) single-dose vial, Instructions for Use (revised April 2026). (link not shown: non-primary host)
9. Semaglutide (Wegovy), US prescribing information. (link not shown: non-primary host)
10. Bremelanotide injection (Vyleesi), US prescribing information, DailyMed. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=f1d0c1b5-2f39-4bad-a6a4-0066e3ad5dcf
11. Semaglutide (Ozempic), US prescribing information. (link not shown: non-primary host)
12. United States Pharmacopeia. General Chapter <797> "Pharmaceutical Compounding — Sterile Preparations" (revision official 1 November 2023). https://www.usp.org/compounding/general-chapter-797
13. American Society of Health-System Pharmacists. "The Pharmacist Guide to Assigning a Beyond-Use Date to a Compounded Sterile or Nonsterile Preparation." https://www.ashp.org/-/media/assets/pharmacy-practice/resource-centers/compounding/docs/The-Pharmacist-Guide-to-Assigning-a-Beyond-Use-Date.pdf
14. U.S. Centers for Disease Control and Prevention. "Preventing Unsafe Injection Practices." https://www.cdc.gov/injection-safety/hcp/clinical-safety/index.html
15. Bacteriostatic Water for Injection, USP (0.9% benzyl alcohol), US product labeling. (link not shown: non-primary host)