I know it's not a scientific study, but it have changed my mind. Years ago I though that weed was mostly inoffensive.
Interestingly, I heard an expert to comment that the weed of now it's not the weed of then, but many times more powerful because the plants have been selected for it.
That observation, by itself, does not say anything about what's cause and what's effect. It may very well be that cannabis causes all these things. It may also be that the sort of people who have psychological problems are drawn towards smoking weed either because of these psychological problems (i.e. seeing cannabis use as a relief for mental stress) or because of a common cause of both desire for cannabis and psychological problems.
I'm not saying which is true (not an expert on the subject), just that you cannot deduce it from your observation.
Just to be clear, I'm talking about heavy users here, not occasional users.
I don't think is a so strange prior to have. After all, heavy use of almost anything, have secondary effects.
I understand, this is an observation, not an experiment.
Anyway, as a follower of Bayes, I have updated my probabilities.
They would be a great example of a person who acts "too safe" all of his life not realising that it's his own fear that basically keeps him in his sandbox, when there's a whole world out there (BTW, I am not speaking about anything related to the New Age, as that could be interpreted - just the risks one could possibly take in general).
Two of my smartest friends are one who doped every day for a few years and the other one who practically never did drugs. Both are considered quite weird by the general population, and both know that and they know how they could manage others (but not vice-versa).
Now quite frankly I find that most of the people will never realise that drugs work well when they're done in balance with the other things in life. And the fact that occasional stressing of your body is quite beneficial in the long term, simply because it works just like training your physique.