I'm very confused by the storyconstantly mentioning the MC addiction, yet when offered unknown drugs, "I've never done anything like this before"???
Drug is far to be the only thing that can lead to addiction ; it's one of the few things that lead to a physiological addiction, but addiction can also be emotional. And most addiction are destructive in a way or another. Even the most innocent things, like stamp collection by example, can become addictive, as long as it fill something in your life.
It's the same scheme whatever your addiction. It start innocently, then you discover that it put you in an enjoyable state of mind (whatever serenity, excitement, etc.), therefore you do it more often, more longer, more seriously. The deeper you'll go, the more you'll do nothing else. And the more you'll do nothing else, the deeper you'll want to go, because it now don't just fill some hole in your life, it fill the hole that your life has become because of this addiction.
And it's why it's really difficult to quit, especially without help, because it's a vicious circle that left nothing else in your life.