I think of myself as a generalist when it comes to drugs, it's like the urge to experience as many different substances is overwhelming. So far the substance i consider myself to ever have been addicted to is mephedrone.
Was virtually a daily user back when you could get a gram of 100% purity on ebay for ?7. I think the legal high ban did me a massive favour. Kind of a good job I didn't know about my current hook up method back then, or who knows where I would be now.
I know it's playing with fire, my latest try is heroin(!) after working my way the the lesser opiates, actually pretty disappointing after all the hype, can't see myself getting addicted, not worth the money or bruised veins IMHO.
I guess it would be fair to say I have a psychological addiction to getting high, just the substance that changes.