Happy people normally don't end up with drug dependencies. Happy people do sometimes abuse drugs, but normally people who end up with a dependence are ones who trying to keep that hollow empty feeling of major depression at bay. Have you ever met a happy well balanced junky?

Often drug problems are not really the root problem, but just another symptom of a much bigger problem in a person's life. Feelings of helplessness, lack of control in life, that holly empty feeling of depression, not being able to see a gainful future, or just feeling like you don't truly have anything worth living for. Sometimes it's just a way to not have to face the real problems in life that you just can't bare to bring yourself to think about or address. Other times, especially with stimulants they are overworked, overwhelmed, and are using them to just keep going.

Ofc, maybe it's a chicken and egg situation. Was it the drugs that brought a person to that place or was it because they were already there that they were vulnerable to a substance dependency? Then again, most well adjusted upbeat people that I've know, who have gainful but manageable things going on in their lives, tend to just treat substances at most as a recreational waste of time because they have things in their lives that are more important.