there is definitely a link between marijuana use and emotional disorders such as schizophrenia, however little to no research has been done into whether this is causal or not (in either direction). It may well be that prolonged marijuana use gives you a higher chance of having schizophrenia, or else it might be that schizophrenics are more likely to find themselves wanting to smoke marijuana (either for chemical reasons, or more likely through societal channels).
Also, for anyone, regardless of age, they are always learning and developing their personality. if they smoke the whole time, then their personal development is done under the influence of marijuana (or it can be speed, whatever), so when you think about it, the person they become depends on their perception based on the drugs in their system. Society has seen this most seriously with Valium, which ruined the lives (in my opinion) and upbringing of many children whose mothers were on Valium for a good few decades, not to mention ruining the lives of the mothers as well, sleeping their waking lives away.
But this is the sort of research that is not done because of stigmatisation, in the media and in government, and it's the sort of information that doesn't get disseminated for the same reason, you only hear this stuff on the "grapevine", and you never know who's telling the truth. everything i just said might eb rubbish for all you know!
that's why i advocate our society having a more honest approach to its problems (our problems), including drugs, environmental health, global poverty and economic injustice. While we continue to sweep these issues (and others) under the carpet or file them in the somebody-else's-problem bucket, nothing will get done and these problems will compound, and we all have to live with it then.
