expiry date
The expiry date is the calendar date stamped on a medicine after which it should not be used — the front-of-pack translation of the shelf life into a day you can read at a glance. It is the date until which, and only until which, the manufacturer stands behind the product.
It is calculated as the date of manufacture plus the approved shelf life, then usually rounded down to the end of a month (so an expiry of 06/2027 means the product is fine through 30 June 2027). It assumes the product has been kept unopened in its original packaging under the labelled storage conditions; mishandling can make a product unfit well before this date.
An expired medicine is not necessarily dangerous on the dot of midnight; rather, the date marks the point beyond which the manufacturer no longer guarantees full potency and quality, and degradation products may exceed their limits. For most solid oral drugs the main risk past expiry is gradual loss of potency, but some products (notably certain antibiotics and biologics, and any sterile preparation) should be treated as genuinely unreliable once expired.
A caveat worth stressing: opening the pack often supersedes the printed expiry date with a much shorter in-use or beyond-use date — for example a reconstituted antibiotic suspension good for only 7 to 14 days refrigerated, regardless of the bottle's long printed expiry.
A glyceryl trinitrate sublingual tablet bottle may carry a two-year expiry date, but once opened the tablets lose potency by sublimation within weeks, so patients are advised to discard and replace the bottle a few months after first opening — the in-use date, not the printed expiry, governs.
Printed expiry vs in-use date: glyceryl trinitrate shows why opening can change everything.