Welcome to SR! Ann has already given you some good suggestions. I have a 31 year old daughter who's an active addict/alcoholic.
Just a little information for you-there is no 'finishing' NA. Narcotics Anonymous is a 12 step program that gives recovering addicts the tools to live life on life's terms, to cope, in effect, without the use of drugs.
I will certainly keep your son in my prayers, and please continue to post! :ghug :ghug