Here's one definition (verb):
To cause to become physiologically or psychologically dependent on a habit-forming substance.
Here's another (noun):
One who is addicted, as to narcotics or a compulsive activity.
I have to admit, there's a pretty big stigma attached to that word. I just spent some time unraveling my association with this word and concept, starting with the now overplayed tale of James Frey and "A Million Little Pieces." In the meantime, I have our school nurse dropping by my room once a week to serve up a little slice of curriculum called "Too Good For Drugs." Since it's fourth grade, most of the time is spent teaching kids how bad smoking cigarettes can be, and we use the "a" word to describe why someone can't stop. A couple of the kids in my room offer up their testimonials - about a mom or uncle who "caught cancer." We also teach kids what to do if they are offered drugs. We tell them how bad peer pressure can be, but they need to be strong. They make earnest promises that they would never get messed up with that stuff.
I know for a fact that the kid who lives in the apartment building across from us went to public schools right here in the same district where I've been teaching for the past nine years. Given his age, every indication points to this kid getting the same education that the kids in my room are getting. I have to know that this kid made the very same heartfelt assurances to his teacher and his classmates that he would never let himself get hooked on drugs. This kid smokes - cigarettes (probably because his mother does), and marijuana (probably because he sells it). There's a hole in his life, and he fell through.