I would educate yourself on symptoms of drug use (beyond being disrespectful, which happens with many adolescents). If he were truly showing real signs of hard drug use, you could insist for his own safety, but only if you could show why you were concerned (and not because of the basic disrespect issue). If it is about disrespect, I would suggest family therapy first, if nothing else is working.
this is just dumb, there is a thing called mood swings