There really should be an acceptable alternative in the U.S., since accidental poisoning and overdoses frequently happen with leftover medication improperly stored.
Correction to my previous post: It is up to each state to determine whether drugs can be recycled or returned to pharmacies. However, almost all states that do have recycling programs (or allow returns) specifically exclude controlled substances, making it a moot point for this thread/forum.
As of now, there are few simple options for people wanting to responsibly rid themselves of used meds.