Welcome to the family.
If your son is of legal age and independent there's not much you can do for him, sorry to say.
The addict himself has to want to get clean, we can't 'make' them want it.
We have a forum here dedicated to those whose lives are touched by addiction. Give it a look. The people there understand what you're going thru.
Friends and Family of Substance Abusers - SoberRecovery : Alcoholism Drug Addiction Help and Information