[LongWayHome]

As an occasional sufferer of seasonal allergies, I can assure you that Benadryl has a short shelf-life after the expiration date. The stuff will not work well, or at all, shortly after its use date.

Antibiotics, on the other hand, seem to last many years after its expiration date.

[Vigilanteman]

Putting an expiration date on antibiotics is almost like putting one on table salt. There just isn't much in them to deteriorate.