Some are predisposed, some are not.
"Back in the day" we were taught about an "X" factor, that anyone might have.
If you don't do drugs/alcohol, you will not be affected even if you have this factor.
That just shows how much (little) they knew 'back in the day'
I mean, let's not forget here that a number of drug addicts have begun with prescription medication - read, drugs (including pain meds or sleeping aids) that are not only NOT prohibited (like crack) but were specifically prescribed, to them, by doctors, for any number of perfectly legitimate medical reasons. And even non-legitimate reasons: with the current tendency to prescribe psychotropics to children as young as toddler-aged, with little to no chance given to psychotherapy as a way to overcome or heck, even just manage even relatively minor or non-complex behavioral issues or other difficulties, I fear we will be seeing an increase in the number of people who reach addiction through such a path
I'm sure you're not suggesting it's a viable option to avoid all medication stronger than over-the-counter in the hopes of avoiding addiction