
It used to be that people were told to flush old, expired, or unneeded medicines down the toilet, but out of environmental concerns that is not the case anymore.
It is also important to get rid of medication safely, so it doesn't pose a risk for children who may get ahold of it. Accidental poisoning is a very real and dangerous threat for children, young children who may not know any better and older children wishing to experiment.
This article explains how to safely get rid of old medication.