From what I have learned and experienced there is definitely an addictive 'personality' although these days many professionals call it an addictive gene. They know that if a parent is an addict the offspring are 4 times more likely to be one also, even if raised by someone else in a household where no drug/alcohol abuse is present. I found out late in life that my father was an alcoholic, he died from it when I was too young to realize what was going on.
Also, in the field they talk about 'cross-addiction', giving up one addiction for another. An addict is an addict no matter what their current addiction is. At least that is what we were taught in rehab. It was certainly true with me. I didn't run into trouble with alcohol until I had gastric bypass surgery and couldn't eat - but I could sip wine all day. Fear of cross-addiction is why I never let a Doctor prescribe any type narcotic for me. I've never, ever abused them but my experience in going from food to alcohol makes me extremely cautious about ANY mood-altering substance.
EagleHeart you are so right about it taking over. When someone is actively using you are talking to the drug, not the person. And the drug is only concerned with being sure there is more on the way! The person is only concerned with finding more and not interrupting the supply chain!