expired drugs

What's the deal with the "discard after one year" label on pill bottles? Is it based on real science? Or, is the FDA just trying to get you to send in "outdated" medicines, especially prescription opioids?
Today s Wall Street Journal examines an age-old question: What does the expiration date on a drug mean? Is it safe to take drugs after this date? Do they still work? The Journal piece gives some general guidelines most of which are correct but there is information that is not included, says ACSH s Dr. Josh Bloom, and what is not there is probably more interesting.