A peptide mixed with bacteriostatic water keeps up to 28 days in the fridge, counted from the day you mix it. Mixed with plain sterile water, it keeps 24 hours.
Your peptides are degrading right now
Storage is where quietly wasted money accumulates, because degradation is invisible. A vial that lost half its potency looks exactly like one that did not.
The matrix
| State | Storage | Duration |
|---|---|---|
| Lyophilized powder | Refrigerator 2–8°C | Several months |
| Lyophilized powder | Freezer −20°C | 1–2+ years |
| Reconstituted with bac water | Refrigerator only | Up to 28 days |
| Reconstituted with sterile water | Refrigerator only | Use within 24 hours |
| Opened bacteriostatic water vial | Room temp or refrigerated | 28 days |
Our reconstitution guide gives slightly wider figures for unreconstituted powder, 1–2 years refrigerated and 2–3+ years frozen, and notes some peptides hold 4–6 weeks reconstituted. The Playbook's 28 days is the conservative number and the one to plan around, because it is the beyond-use date for an entered multi-dose vial rather than a claim about the peptide.
The four critical rules
Never freeze reconstituted peptides. Ice crystals form and physically destroy the molecular structure. This is irreversible and total. The freezer is for powder only.
Never leave peptides at room temperature. Heat accelerates degradation. Return the vial to the refrigerator immediately after drawing a dose, not after you finish the injection and tidy up.
Store vials upright. This prevents the solution from sitting in permanent contact with the rubber stopper, which can leach over time.
Do not mix different peptides in the same syringe. We found no study showing it is safe.
The 28-day clock
The 28-day limit on a reconstituted vial is not an estimate of when the peptide breaks down. It is a beyond-use date. CDC's rule for a multi-dose vial is that once it has been entered it is dated and discarded within 28 days, unless the manufacturer states another date and never past the original expiry; USP ⟨797⟩ sets the same ceiling from the other side: the assigned beyond-use date or 28 days, whichever is shorter.
The preservative is not what grants those 28 days, and it is not a safety net either. CDC is explicit that it has no effect on viruses and does not give complete protection against bacterial contamination. What benzyl alcohol buys you is the ability to enter the vial more than once at all.
After 28 days, the solution may still be chemically intact and no longer reliably sterile. Those are different failure modes and the second one is the dangerous one.
The same 28 days applies to an opened bacteriostatic water vial, from the date of first puncture.
This is why labelling matters. Write the date on the vial at reconstitution, and let the label do the remembering.
Three dates on a vial
A vial can carry up to three dates, and the earliest one wins.
The expiry date is set by the maker of a sealed vial, such as bac water.
A BUD, or beyond-use date, is set by a pharmacy for a vial it prepared. The pharmacy standard, USP ⟨797⟩, has it printed on the label.
28 days after the first puncture is CDC's limit for an opened multi-dose vial, unless the maker states another date. For a vial you mix yourself, the first puncture is the day you add the water.
Put together: once a needle has been in a pharmacy vial, USP ⟨797⟩ gives it until its BUD or 28 days, whichever comes first. No vial goes past the maker's expiry date. Write the date of the first puncture on the label, beside the others.
The sterile water exception
Reconstituting with plain sterile water gives you a 24-hour vial, single-use, because there is no preservative at all.
Three compounds are on our sterile-water-only list: oxytocin, NAD+ and KPV. For those, prepare the dose and discard the remainder within 24 hours.
For all three, sources disagree, and Claritide takes the cautious side: sterile water, and 24 hours. Our own list says sterile water, dosing guides mix them with bacteriostatic water, and we found no study that settles it.
hCG is not on the list. Its FDA labels mix it with a diluent preserved with benzyl alcohol. Novarel's label says to refrigerate the mixed vial and use it within 30 days. Pregnyl's says the mixed solution is stable for 60 days when refrigerated.
For everything else in this library, bacteriostatic water is the correct solvent.
Peptides that degrade faster
Some peptides are more fragile than others. Those containing cysteine, methionine or tryptophan residues are more susceptible to oxidation and may have a shorter reconstituted shelf life than the general 28-day figure.
If a specific compound's guidance is shorter than 28 days, follow the specific guidance.
Taking a vial on a trip
We found no study of how a mixed peptide vial handles a trip. The closest published advice is for insulin, which is also injected and kept cool. CDC's travel tips say not to keep it in a checked bag, where it can get too cold. They also say not to store it directly on ice, and suggest a cooler with a gel pack.
On US flights, TSA's pages allow medically necessary liquids above the usual limit, gel packs to keep them cool, and unused syringes with injectable medicine. Tell the officers at the checkpoint.
Whether a research peptide counts as medicine there, and what another country allows, are legal questions this lesson cannot answer. CDC notes that a medicine allowed at home may be banned elsewhere.
The discard rule that overrides everything
Discard if you see cloudiness, particles, discoloration or an unusual odour, regardless of how long it has been. A vial reconstituted yesterday that looks wrong is a vial to throw away.
Inspect before every single use, not just the first.