It sorta left out gross personality changes, changes in activity patterns, and changes in social contact groups. This is something especially to be alert to and aware of with teenagers. Even 'high functioning' users will show all three to some extent. Although other factors may apply (puberty is a b**dh), noticing the changes might give someone a chance to catch their kid before things start to really get nasty.
Never say 'it can't happen with my kid', but keep in mind accusing someone who isn't using might backfire at that age, and just might tick them off enough to get them to try something they haven't.
The biggest change an addict undergoes as they get hooked is that they don't care about anything (or anyone) but the drug(s), with some 'caring' for buddies who use (who are often a source).
The complicating factor is that with puberty, interests and peer groups commonly change anyway. But when kids quit caring about the basic things they used to care deeply about without replacing them with something else that seems like the next normal step, or having a reason for turning away from longstanding friends, there may be a problem.