Sorry this is a rather quick/rambly post as dashing today. Apologies for not responding to everyone!
I don't have a clue either Squeegle but some of these links may be of interest:
Supporting Your Child Drugs and Alcohol
Young Minds drug use
Mentor
I don't know what I what do in your shoes but I suppose I would confiscate and try and find more info before confronting??? Forewarned is forearmed and all of that. Good luck with it.
Same here Tickling you would never know that your first lang wasn't English! You "speak" it so well!
I must admit I didn't get on well with CBT at all, although I only went to six sessions. It was all so clinical (guy explaining it was very cold and robotic) and he just drew squiggles on a white board and droned on without making eye contact and it took me right back to fifth year maths (shudder). I went expecting a bit of humanity and understanding and came out with a notebook full of diagrams that I couldn't comprehend. I remember coming away full of admiration for his tidy house and very large over-sized sculpture of an eye
.
Having said all of that Ticklingcheese I am so glad that it worked for your ds and that he is doing so well now
He was (and is) very lucky to have you there to support him. Your description of him as the "nicest person imaginable" also brought a lump to my throat
.
Never apologise for venting Parsley (that's what this thread is for) and sorry the holidays are hard work at the moment! I always look forward to them (like I always did when dd was 8 or 9 for example) and then the reality hits ... . I've just scarfed down a load of Easter egg and I really must stop it. 
Noted about D and B12 vits! And the point about 'Findmyfriends'! All very useful x
Hope your ds will agree to take part in some activities Lightandairy and that he enjoys them!
And
to all Po Ts such as Auberginerus and others who are struggling with teen motivation and exams. Or motivation to attend counselling in some instances.
Parsley's advice of "one day at a time" is excellent I think. It's too stressful and wearisome to think long-term sometimes when we are in the middle of the mire "or our little hell" as Xeroxarama puts it.
Waves to Billy Staywithmemyblood Whattodofgs Gandalf McMen Whoops75 Daintytoes and everyone I have inevitably missed!