I have a full bottle of Darvocet sitting in my medicine cabinet. My doctor said to get rid of it so nobody can accidentally get into it. We all know (everybody NOD YES) not to flush medications down the toilet because it all comes back into the waterways and drinking water supply. Aside from your local pharmacy, Department of Health or Board of Pharmacy that might have a take-back program, you can also try Earth 911 or the Starfish Project. The latter takes certain medications for distribution to the people of Africa.
We also see signs in public restrooms not to flush anything other than toilet paper. That should hold true for our own homes, too.