I think you are great parents and that is obvious!
I know that some here have ordered drug tests on Amazon. You can even buy them in bulk - if that is the course you choose to take. I did not as I said because I KNEW he was using stronger drugs. Then if you find out that he is, you have to decide your next step. If he is clean other than MJ that would be a relief in some ways - for me it would have been.
Either way, your son is not a minor nor a little boy. And like the rest of us, you want him to grow up to be a happy, productive and responsible adult. That is really the end goal here for all of us. We know we are not going to live forever and as parents, that at the very least is the legacy we want to leave behind.
I do hope that everything that you have in place works for you. We tried everything and nothing worked for us because our son just didn't care most of the time and when he did it was short lived until he binged again. Of course now he is clean and doing extremely well and we are getting to know our son again.
Keep us posted.