It's such a thin line, really...the Thinnest line of all, the line between use and abuse...said Irvine Welsh...
I think it's a bit like guido said....when you find yourself doing stupid, very stupid and dangerous things that you would NEVER normally do to get a hit....
when you find yourself prioritizing and obsessing about the drug in question.
when you need it to even leave the house
when you stop cold turkey and you're in for a world of shit
when you hallucinate unless you dose...
when you lie, cheat, steal even your closest mates to get a bit more of the drug in question.....
I think you're pretty addicted by then...
for me, non addict use, as in casual user, means the use may vary in when you do it, why, and how often...as in you don't really program a time and a place, it just happens, then you don't think about it for a long while, then, when the occasion arises, you take a dose...
when it becomes systematical and an every day, around the clock thing...you're fucked.
I have driven 300kms while withdrawing from GHB to get another bottle of it, and then drive back another 300kms while passing out...no fun...