Don't panic
This is something to keep an eye on, but it's not like people just started flushing old medicines down the toilet last year. Don't freak out just yet.
My wife's a pharmacist, and we properly recycle expired medicines (I used to flush them myself in the old days). In fact, they had an environmental faire at City Hall Saturday, and we took a bagfull in then. It gets incinerated. Don't know what happens to the air...