And it may begin as a choice, but for some people, the choice is quickly lost. Experimentation is always the initial step. And this is the step most people understand. Part of being a teenager, growing up, is that feeling of being invincible. Teenagers feel that they will live forever.
Parents accept that.
For many, experimentation quickly moves into use. Usage may start as a weekly thing. Just a party on the weekend. This phase of the disease may last for a while. Friends are using, everyone's having fun, and the drug makes you feel better.