APO 097

Found an oblong, white pill on the floor of our basement today.  It has APO on one side and 097 on the other.  Looked it up on-line (what would we do w/out the Internet?) and  I found out that it's Paxil.  I tried to find out if this medication is typically abused, but couldn't find anything.  What the heck?  I know he will deny.  I know he didn't get it from our doctor.  *Since he's 18 - it's possible but I know it isn't the case.  Wonder what else he's doing?  I also know that it isn't our middle guy.  He took himself off of these kind of drugs years ago that were prescribed by a doctor - it's the last thing he would want to do. Besides - he's doing extremely well.  There is no doubt in my mind that it's my youngest. 
update:  My husband told my son that I found an anti-depressant laying on the floor and asked him about it.  He told my husband that it was probably one of the pills he took when he was on medication.  That didn't work because he was on Welbrutin and this pill was Paxil - nice try.  Since that wasn't the "right" answer he says it must be his brother's.  
He didn't come home last night.  No surprise.  Same ol - same ol.  Every time I think we don't need to go back to the counselor - something "happens" just before.  Not sure how effective this guy is but for some reason it does give me some peace of mind.  I know I'm fooling myself thinking that I'm doing something - but whatever it takes.