Storage and stability: what is actually known

What approved peptide labels say

These are the only peptide storage figures that come from stability testing a regulator has reviewed. They are quoted from the current prescribing information published on DailyMed, the United States National Library of Medicine label service.

Three things those labels show

The number is specific to the product, not to peptides. Semaglutide gets 56 days after first use. Tirzepatide gets 21 or 30 days depending on which container it came in. Same drug class, different numbers, because each came from testing that particular formulation in that particular container.

The clock is defined, and it differs. Semaglutide counts from first use. Tirzepatide's single-dose 21 days counts total time out of the fridge. A figure is useless without knowing which clock it runs on.

Freezing is disqualifying, not recoverable. Both labels say discard, not thaw and inspect.

Why there is no equivalent number for unapproved compounds

A storage figure on an approved label exists because the manufacturer ran stability studies on that exact formulation and a regulator reviewed them. For a compound sold as a research chemical, no such study has been run, reviewed or published. There is no manufacturer accountable for the formulation, no regulator who has looked at it, and frequently no certainty about what is in the vial.

That is why the widely repeated figure of 28 days for a reconstituted research peptide should be treated as a convention rather than a finding. We could not locate a primary source for it anywhere: not a stability study, not a label, not a pharmacopoeial monograph. It is quoted from one vendor page to the next.

The underlying chemistry is real and well described. Peptides in solution degrade through deamidation, oxidation, hydrolysis and aggregation, and the rates depend on temperature, pH, buffer, light and the specific sequence (review, PMC9610364). What that literature does not provide is a shelf life for a particular unapproved compound, reconstituted at home, in water of unknown quality, in a vial of unverified contents.

About USP chapter 797, which is frequently misquoted

Vendor and clinic pages often cite USP General Chapter 797 as the authority for a beyond-use date. That chapter governs compounding pharmacies, the facilities preparing sterile products under controlled conditions, and the dates it sets are assigned by the compounder based on their own process, environment and sterility assurance.

It was not written about a person reconstituting a vial at a kitchen bench, and applying its numbers to that situation borrows authority the number does not carry there. A beyond-use date is also not an expiry date: an expiry date comes from the manufacturer's stability testing of a finished commercial product, while a beyond-use date is a limit the compounder assigns to their own preparation.

What we will not tell you

We will not give you a number for how long an unapproved compound lasts once mixed, because no honest source for that number exists. Anyone who gives you one with confidence either has data nobody has published, or is guessing and not saying so.

What is reasonable to say is that degradation is faster warm than cold, faster in light than dark, faster with repeated temperature cycling, and that a product which has changed in appearance should not be used. None of that converts into a date.