Plantman, djugurba has made many good points. I teach behavior disordered children and most are there because of overly permissive parents or parents who were just too lazy to raise their kids or parents who were too wrapped up in their own lives for their children to come first. I am not saying that you are any of these, I don't know you and certainly don't want to make a judgement call.
Aklim also makes good points. A drug use kit can be purchased at any drug store - they may not be out on the shelves. Ask someone that works there. If they don't carry them they will be able to tell you where to find one.
As far as suicide threats go - I treat any threat as valid. Usually when a child threatens suicide they are immediately taken to the emergency room and admitted for observation. If he is serious then he will get help. If not then at least he will have to suffer the consequences of having to stay in hospital for at least 48 hours with strict observation. Either way - he gets the point.
It is easier now to do something about this than it is to wait. As I tell many parents - it is a lot easier to deal with an out-of-control 3 year old than an out-of-control 13 year old. Same scenario with your son. It is easier to deal with him when he is 16 or 17 and you have some say so than when he is 20 (and don't anyone lecture me about "he's an adult at 20". Your child is always your child and it is just as hard to watch them make a mistake at 35 than at 15).
TAKE HIS DRIVING PRIVELAGES AWAY IMMEDIATELY - AND HIS KEYS!! It is also easier to keep him under your thumb when he is not mobile. Make him earn this privelage back - and don't make it easy for him. Spy on him if you have to - and don't anyone lecture me about privacy - there is not a person here who didn't sneak around about something when they were an adolescent.
Do what you have to do to get him back on track - even if it means missing sleep on your part. My parents camped out at the doors one time when my sister threatened to run away. They put alarms on her windows so she could not sneak out - you get the point. Do not make it easy on him at all!! I know this sounds harsh - but do you think he was thinking of you when he did what he did? He sure is not making it easy on his parents - and be sure and remind him of this.
Sorry for the ranting and raving! This is a subject that really strikes chords in my heart.