Retest dates and shelf life on research peptides, explained

Written 23 September 2026 by the trade desk. About 2 minutes to read.

Every certificate we issue carries a retest date, not an expiry date. The two are often confused, and the difference decides what a laboratory should do with a vial that has been in the freezer a while.

Shelf life

Twenty-four months from manufacture for lyophilised lines held at minus 20 degrees Celsius, and the same for solutions held at 2 to 8 degrees. The figure is the period over which the batch is warranted to meet its specification if stored as stated.

The retest date

The date on which the batch is due to be analysed again before it is sold on. It is not a cliff. A batch a day past retest has not changed overnight; it has reached the point where the warranty needs fresh data.

What happens on our shelf

Stock past its retest date is removed from sale automatically and cannot be shipped. A batch is re-analysed against the same specification; if it passes, a new retest date is set and the analysis is recorded on the certificate; if it fails, it is withdrawn. The number of retest cycles is capped, because a batch cannot be re-warranted for ever.

What it means for stock you hold

Keep the certificate with the batch. Past the retest date, either have the material re-analysed or treat it as unwarranted. Storage conditions matter more than the calendar: a vial that has been through a freezer failure is not covered by any date.

Why the date is not simply longer

A peptide in a dry cake at minus 20 degrees changes very slowly, but it does change, and the sequences most at risk are the ones with residues that oxidise or deamidate. Twenty-four months is the period for which the data supports the specification across every line we carry, not the period after which a vial is spent. Extending it would mean a longer study for each line, and the retest mechanism does that job one batch at a time instead.

Reading the two dates on a certificate

The date of manufacture is when the batch was filled, and the month is also encoded in the batch number. The retest date is the manufacture date plus the shelf life, or, after a re-analysis, the date of that analysis plus a new period. A certificate with an analysis date later than the manufacture date by a year or more is a retested batch, and the certificate will say so.

Picking order

Stock is picked oldest in-date batch first, so the batch that reaches you is the one with the least time on the shelf behind it, never a batch closer to its retest date while a fresher one sits behind it. If a laboratory needs the longest possible remaining period for a planned study, say so on the order and the desk will pick accordingly.

Applies to

Semaglutide among others. Every compound.

Read next