A number of years ago, I had a severe back injury, and opted not to have the surgery I was told was virtually necessary to fix the problem. So, to sleep, stand, or sit, I had some pain medications prescribed and they got me through the day, not particularly effectively, but the pain was really something without them.
At about month four, my pharmacist was refilling the prescription, and he mentioned that it was the strongest pain killer available, it was a barbiturate, and that at the rate and duration that I was taking them, I was very likely now addicted and that I ought to obtain a consultation about that.
Oh great. Nobody had said a word about any of that at the time. I went back to the office, thought about it, and tossed the pills. I thought, well, now I get to see if those movies showing horrendous withdrawal symptoms were true.
The results? Other than the pain, nothing.
I asked the neurologist about it, and he was quite surprised, but he said there are distinctive "personalities," I happened to be one of the fortunate few that was a "non-addictive" personality, and that given the experience and the drug involved, an extreme outlier of a non-addictive personality, but that at the other extreme were people who addicted at the drop of a hat, to coffee, behaviors, and especially drugs of any kind, and if it was to the addictive pain killers, he said those were nightmarish situations for those people and invariably -- he used that word -- led to criminal behaviors; the compulsion was just that strong. Fine people, turned criminals because of that biochemical trait.