Cannabis & Mental Illness

A possible future legalization of cannabis (marijuana) would lead to wide commercial access of cannabis and an increase in the cannabis-using population, as found in other countries. As reported in many studies, increased cannabis use leads to a later increase in psychoses, especially schizophrenia. T.H. Moore and colleagues in the Lancet, 2007, concluded that there was “sufficient evidence to warn young people that using cannabis could increase their risk of developing a psychotic illness later in life”.

For example, cannabis use in the UK increased four-fold between 1970 and 2002, and increased 18-fold in the under-18s. They estimated that new cases of schizophrenia would increase by 29% in men between 1990 and 2010. In fact, it was later found that the annual new cases of schizophrenia and psychoses increased from 49 per 100,000 in 1996 up to 77 per 100,000 in 1999, an increase of 58% over three years.

In the canton of Zurich, Switzerland, cannabis use in 15-16-year old boys went up from 15% in 1990 to 50% in 2002. This was followed by a doubling in hospital first admissions for psychosis and schizophrenia in those aged 15 to 24. A major study by Zammit and colleagues in 2008 found that 1.1% of 1,648 Swedish men conscripts for military service who had ever used cannabis prior to 1970 subsequently developed schizophrenia, two-fold higher than those who never used cannabis. This went up to six-fold higher in those who ever used cannabis 50 times or more.

In general, studies found that psychosis occurs 2 to 8 years after a significant amount of cannabis use, and that the risk of psychosis is higher when cannabis use starts at an earlier age. An Australian study of 83 reports found that cannabis users had an age of onset of psychosis that was 2.7 years younger than non-users. Alcohol use was not associated with an earlier age of psychosis onset. In The Netherlands men cannabis users had a first psychotic episode 7 years younger than non-users.

Any future increases in cannabis-associated new cases of schizophrenia would add to the current high rate in Canada and the USA. M.-J. Dealberto at Queen’s University in Ontario found that the rate of new cases of schizophrenia in Canada is about 26 per 100,000 per year, considerably higher than the countries outside Canada which average about 12 new cases per 100,000 per year. (Quebec is even higher at 40.)

In addition, such an increase in new schizophrenia cases would need to be matched by significant increases in psychiatric hospital budgets and in community-based housing and welfare. For example, Ontario’s two major psychiatric centers (Ontario Shores Centre for Mental Health Sciences in Whitby, and the Centre for Addiction and Mental Health in Toronto) have a combined annual budget of about 400 million dollars, with

approximately half assigned for schizophrenia. Across Canada, such budgets would need major increases. Considering that Ontario, for example, receives about 1,100 million dollars each year for tobacco taxes, a cannabis tax might cover the increased needs of the psychiatric hospitals and the community housing.

While the majority of cannabis users would not develop schizophrenia, the wider use of cannabis would lead not only to more hospitalizations of the new cases of schizophrenia, but also to an increased confrontation of psychotically disturbed young men with police.

Although there are valid medical uses for cannabis in cases of resistant epilepsy, and various painful chronic illnesses, wider use of cannabis may also be associated with drowsy driving and car accidents.

Almost all aspects of cannabis use and the related laws are contentious. Whatever laws are adopted by government may have to be a compromise between medical need and a reduced burden to all citizens.


The author discovered the human brain’s dopamine receptor for psychosis and all antipsychotic drugs.

Source:   blog Oct. 17, 2013.

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