I know that all of my meds I have now have a 1 year expiration date right on the label from the day they were dispensed.

Over time, some meds gain potency, making them toxic while others lose it. The safest thing to do with 3 year old sleeping pills (or any old prescription) is flush them down the toilet because you don't know if they are more potent or weaker. (I only say flush them because this is what my pharmacist has told me.)

As far as OTC drugs, many of them have the expiration date printed somewhere on the bottle or blister packs, taking the guesswork out of it.

Dolfin