Despite being clean myself, I've had a bit to do with drugs & alchohol through my mates, girlfriends & some of my family. One of my friends was totally irresponsible, I watched him screw himself up & get institutionalised through cannabis abuse. Yet even after he got out, he still continued to abuse them, I don't know what he's doing now as I eventually got fed up & kept my distance from him.
It's absolutely rife amongst young people & despite all their 'streetwise knowledge' their ignorance of the hard facts & the impact it can have upon your mental health is shocking.