I really think there's more to addiction than introversion vs. extroversion. As Yippy said, there is genetics. There is also just where you were raised and what you saw as a child/what you were exposed to or likely to be exposed to as a teen or child.
There was also an interesting study on rats in which rats who had stronger social networks and more stimulation tended to become less addicted to cocaine. So whether or not humans are like rats, IDK, but it seems to suggest that addiction can also relate to the social support network you have or the access to community.
There are also a lot of writers and artists who have struggled with addiction, many of which are people who are said to be INFPs. Not to say INFPs have to be addicted, but that it just seems the type is associated with creativity, and many creative people have and do struggle with addiction for some reason.
I know that I never wanted to be addicted as a child, and that I hated drugs and substances that could rob me of my loved ones, and that I don't think there's ever been a time in my life in which I viewed it as okay or accepted any addiction without trying to fight it the whole time.
I always advise people to stay away from addictive substances. It's just not worth it. I, myself, am also not interested in substances I've seen my friends get addicted to or sick from. I can't say I've become immune to addiction though. That's obviously not true. I would guess introverts have the benefit of being more cautious about substances, and hesitant against them even if everyone else seems to be doing them or they are available. I've known more extroverts who have comfortable addictions (especially Fe dom) in which they are somewhat addicted to a substance, but it's okay with them because they can use it in socially acceptable ways and can impose limits on it fairly easily. I feel I am often the opposite--I am not okay or accepting of dependence, but I find it's very difficult to stick to limits at times. Not sure if it's related to MBTI or not.
Edit: And to be honest, I've always had a propensity to chase things into extremes. Whether it be romance, eating disorders, "healthiness," righteousness, or chemical addictions. Whether or not that is from my genetics, my upbringing, or my life experiences, I don't know. I do know that the closest, most essential part of "me" that I identify with never wanted to feel dependent and always sensed a discomfort with it, and often fought it in extreme ways.
As a child I used to have nightmares about a ball that would not stay stable on a line. The purpose of the dream was for me to keep the ball stable, but it continued to bounce and fall, and the line would get all jaggedy. Perhaps I wanted the ball to learn to fly and land at will, or to simply gracefully overcome the dips and peaks. Always seeking moderation, but it's so elusive what that is to me. I suppose it's a journey in itself.
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