One example is David Death, who was a massive user of coke. Coke is all good provided you have the self control and discipline to use it, indeed if you do, its a wonderful drug.
Then he progressed to Nubain, then oxys then heroin (probably mixed with both alcohol and weed). And its at this point that for many it goes wrong. For David, he blamed "the doctors for prescribing the stuff to me". I call BS on that. Take control of your own use and blame no one else.
All a matter of moderation, but in my view, the only really productive drugs are stimulants such as coke, (and meth for a select few), provided you know how to use them (and for the vast majority of people they do not have the medical understanding or self control etc to use either).