Put a safe or lock on the room where you keep your meds and make sure you are the only one who has access to the key and keep it on you at all times.
I don't know how old your son is but he is putting you in dire straits both with your PM and the police. If some kid OD's on the pain killers with your name on the bottle your liable. If he's over 17 I would tell your son to move out if I were in your situation.
If he's younger I would ground him for at least 3 months... no TV, no unsupervised use of the computer and only then for school, no non-school related phone calls, no cell phone, no video game consoles, no going to parties or having friends over... let him read books and listen to the radio! He needs to have the seriousness of this impressed on him, so he basically has the fear of God placed in him and won't ever contemplate stealing meds from you again.
It may sound harsh but its not as bad as going to juvenile hall until he is an adult.