Sorry to be replying so late after your first answer I will be giving top feedback immediately after your response - but just a follow up.
I appreciate your expertise in the area, but what about the various cases i've been reading about online (forums mostly) who have had problems?
I can only assume that these people admitted use and subsequently tested positive? You seem 100% confident I will face no sort of problem, but what if I get a particularly un-lenient interviewer? - isn't it largely down to them, and a bit of a grey area if they don't like 'something' ?
One other thing, can you advise on how this may be brought up in my US embassy visa interview - or given that I will test negative - might it not even be mentioned?
And finally...if i'm asked - i'm assuming a straight, no nonsense, truthful response is best, XXXXX XXXXX mistake i made as a 20yr old kid and something I regretted' ?