Mind you I'm 18 now, my mother (having a sister who as a cocaine addict) took me to an NA group, completely disposed of all my drugs and paraphernalia, and tried to open up the doors of communication. This happened when I was 15 (this list of drugs I'd done was pretty long). Getting high was very difficult for about 6 months before I gave up. I think the key was my mom didn't break into my room every night, but knew when I was high and did her work then. As for the other parents, let them know about it.
oh, and psycillicibin is illegal in the US, Slavia is being criminalized in many states, and betel is an old rememdy for worms (which makes it very hard on the stomach, and unpleasant)

drugs, what ever ones he is doing are a serious issue. little drugs lead to more and more and more drugs.
and if it isnt stopped sooner than later, it becomes even harder to stop them.
what it sounds like, is he needs a strong male role model in his life to teach him that the way he is acting is not acceptable. and it may not sound nice, but he needs to be scared into stopping. it sounds like i said, not very nice, but believe me, it has to be done, kids these days think their resiliant to all life's problems.
my brother inlaws friend had a son like yours, and would beat his mom, and his mom got her brothers to talk to him, and they told him off big time and said if he ever did drugs or hit his mom they would send him to therapy and he would not come back till he is 100% clean. never hit her or did drugs since.

my brother was in the same situation, and me being a former drug user, had a talk with him because my mom did not know exactally how to go about it. and i told him all the down sides of drugs, and how it does ruin your life. im a mother now, and he loves seeing my son, but i told him if he kept it up i would not come around anymore and he would not be allowed to see or play with my son, and he stopped. he wasnt seriously into drugs and what not but to instill that fear sooner than later helps.
you should talk about drugs to your son, and let him know your there for him, possibly get him into an activity of some kind to preoccupy his mind and make it unlikely for him to get into drugs.
and like i said, find a positive male role model-a family member, a friend- because clearly his dad is not helping.

but you need to do it sooner than later, because the longer you wait, the deeper into this cycle he will get.

good luck to you.

salvia is not that good of a drug.. everyone I've worked with who has used salvia has had at least one bad trip... and avoided further use, the dosage must be fairly accurate and has a small range between enough to feel anything and not too much to where you forget that you are tripping. Shrooms (psycillicibin) you mentioned is illegal where i'm from but drug tests are hard to find to test for it even our local Juvenile center doesn't test for it I don't believe. I've never met anyone who used betel before. Anyway the bright side is these drugs are non addictive, the bad news is he is experimenting (glad he chose the ones he did) I would worry the most about the marijuana but even that, most rank about as easy to quit as caffeine or easier given the right motivation (in the first yr or so of use anyway and not considering genetic loading for dependency).
I've been counseling teens for 12yr and found that, in what appears to be, his spot harsh consequences beat out all the talking you could do.
DRUG ABUSE = enough consequences and it wont be worth it to use
Dependency = consequences don't really matter and they need counseling
If it were my kid, I'd ground him, take his things make him earn them back with respect and improved grades. (including if needed clothes replaced with "good will" clothes.. law says you have to provide clothing not what name brand they have to be) and maybe even bedroom door off hinges if he doesn't get the point to earn back easily of course. It is SO SO important to stick with the consequences and give a specific thing he has to do to earn back stuff or a specific date. I would also look into in the phone book for a Drug counselor to do an assessment to find out how much of the "tip of the iceberg this is. (make it confidential..from you! or its worthless) and if recommended a substance abuse class 6-24 sessions or so, if done correctly can usually help a lot.

sorry I missed a couple things
"need to tell his friend's parents?" OH yes! I would. without a doubt. but don't expect them to do anything but at least do your part.
"he refuses" WHAT? who's the parent? Call the Juvenile center in your home town if he leaves the house without permission and report him as a runaway then probation will be your back up. consequence him if he refuses and allow him to earn things back when he complies. Stick to this and NEVER give in. don't lose your ground, or your temper and consistently let him know its his choice what to do, but the rules are set. as far as refusing therapy, "take the body and the mind will follow" if it is confidential from you, and it is the right counselor he will resist at first but after a little good ole parental manipulation 90% of the teens I've worked with find out its not so bad after all but they are too short sighted at first to see the positives in it.
"i think he's depressed has add and ocd" that can be screened in the substance abuse evaluation that you make him go to all the more reason to make sure he gets assessed.

thanks for your opinion. i have initiated the process of finding counseling. i want someone who has experience with troubled teens.. i'm trying but i often feel discouraged. i am now in therapy myself. this has been very helpful for me, trying not to blame myself. be proactive not reactive.. if you have more suggestions i would appreciate it.

Not really, the therapy should take care of most anything your willing to discuss... some things take time and some things get worse for a bit till they get better but well, that's life. I'll leave you with this though, its really hard to screw up you kids 99% of the time do whatever seems right to you and as long as you have their best interest in mind they usually turn out ok. Dont be afraid for them to hate you for it, kids hate their parents sometimes its just life and they get over things so so much faster than parents. plus when they hit the maturity level where they change from adolescent (I want to do everything for myself and make my own decisions even if i get my arm cut off doing it..) to Adult hood (maybe my mom was right about a few things) then they will realize how much you tried. till then try not to expect too much gratitude. I've worked in residential treatment settings in the past where the kids were really screwed up but it was amazing how bad the things had to get to screw them up, I would say you and your kids will be quite alright, after all you're doing much better than most and asking for help when needed... Just stay consistent and they will learn faster.