A Harvard University study published a few weeks ago demonstrated that there is a genetic component to how much you like marijuana. That's very interesting because the prediction, of course, is that the more you like it the more you would be prone to take it again, and the greater the probability you would become addicted. We know far more about this for alcohol than we do about other drugs. There's a myth that I was taught when I was a kid, and that was if you take heroin once, you're instantly addicted for the rest of your life. It's not true.
Some people get addicted very quickly, and other people become addicted much less quickly.
Well, it's probably determined by your genes, and by other unknown factors like your environment, social context, and who you are. The fundamental phenomenon of getting addicted is a biological event and, therefore, it's the same everywhere, and the underlying principles that describe the vulnerability, or the propensity to become addicted, are universal. That is a useless and unimportant distinction. First of all, not all drugs that are highly addicting lead to dramatic physical withdrawal symptoms when you stop taking them. Second, when you do have those dramatic withdrawal symptoms with alcohol and heroin, we have medicines that pretty well control those symptoms.