A further note on cannabis useOne of the common arguments on the pro-cannabis side, when considering metastudies such as the one that has got the UK media's panties all knotted, is that they ignore reverse causation. The reason for this is that many studies show that co-occurrence of substance abuse and schizophrenia is common, which suggests that the same factors might impel both or that mental illness causes substance abuse in some way (I do not mean that you have to be mental to take drugs but that the outcomes of mental illness may well lead to substance abuse).
This paper on alcohol use disorder and schizophrenia is interesting. I note the following particularly:
People with schizophrenia and AUD often report that they use alcohol and
other drugs to alleviate the general dysphoria of mental illness, poverty, limited opportunities, and boredom; they also report that substance use facilitates
the development of an identity and a social network (Dixon et al. 1990).
An entire generation of adults with schizophrenia in the United States has
grown up during the era of deinstitutionalization (Lamb and Bachrach
2001). Although residing predominantly in the community rather than in hospitals, these people still have had limited vocational, recreational, and social
opportunities (caused by factors such as illness, stigma, and segregation).
Further, they have experienced downward social drift into poor urban living
settings, where they are regularly exposed to substance abuse and substance-
abusing social networks (Lamb and Bachrach 2001).
Studies into correlation of cannabis use and mental illness do not allow metaconsiderations. This is a problem for any scientific study: it will be looking at the particular without having the means to investigate the more general context. So I think that it's reasonable to conclude that there is a correlation between cannabis use and mental illness, just as there is between abuse of alcohol and mental illness, but premature to conclude why.
Clearly, any discussion of substance abuse is coloured by the model that you use to explain it. Science explains substance abuse by the addiction model, largely because it's very easy to test in mice. You can give mice a ton of heroin and they'll all get hooked. Mice do not live on sink estates, so you can't test the hypothesis that poor social conditions are causative of substance abuse (Rat Park notwithstanding). The higher incidence of substance abuse in lower socioeconomic groups is indicative though. But this model leads policymakers to the conclusion that the drug itself is the problem to be managed, not the individual's conditions. This model has, I believe, become entrenched because it supports the moral case for prohibition: drugs are bad in and of themselves (which is a different thing from saying that they can have bad outcomes).
Should vulnerable people be protected from bad outcomes of their choices? Well, maybe they should. There would be a variety of means to do that, and in mental illness, as this paper notes, managing outcomes in an integrated way, treating the person as the agent not the drug, works.
Should people who might be vulnerable also be protected? That's a more difficult question. If a study shows that children who watch violent movies show increased aggression, should all children be banned from watching violent movies, even if we feel that causation is an open question, and on the whole, we feel that the increased aggression is only seen in children otherwise predisposed to it? Is it better to protect more widely or to target protection (I do not accept that we should not extend protection at all, and libertarians who do are not respectable in my view)? It's possible to argue that if one cannot be sure who the correct targets are, too broad protection is better than failing to cover those who need it.
In other words, even if only some kids become aggressive when watching violent movies and others are not affected, if we are not sure which will be affected or why, but wish to protect those who are, we must extend prohibition to all children. In discussing this, I should point out that I consider protecting children and other vulnerable groups from the outcomes of their own choices by prohibition to be a poor choice on the whole, but something I support where alternative methods of protection are too difficult or costly to use, or simply would not work. In the case of skunk -- we will agree for argument's sake that it is dangerous for some children to smoke high-THC marijuana -- it would be a costly, and likely futile, undertaking to teach children to recognise and reject it in favour of lower-THC weed or to abstain. The same consideration does not apply to adults in my view.
I will not answer comments that are not related to the content of this post. Bitter ranting about ignoring the evidence will just be, erm, ignored. I'm well aware of the evidence on both sides (and I read about the study that showed greater lung damage from smoking cannabis than tobacco -- nothing new, and should not be a consideration for public policy). If you cannot take a sophisticated view of this -- and by that I do not mean you have to agree -- you will be pissing in the wind if you comment.