One thing for me is the denial- the addict in my life didn't think anyone could tell there was something wrong with him. He thought he was acting all 'normal' and cool on drugs despite every one around him saying 'hey there's something wrong with you, why are you acting so strange?' and then he'd try to find an explanation for every comment someone said- I work a lot in the hot sun, I'm really stressed etc. etc. And then when he couldnt make things up about himself he'd start saying there were things wrong with other people, like myself- it's that time of the month for you, you're just stressed about school, you've been mean lately and I don't appreciate it.
People notice when you're doing drugs!!