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March 24, 2007
Cannabis Use / Schizophrenia Correlation Being Studied
Researchers are studying historic trends in cannabis (marijuana) use in the United Kingdom, matching them to new cases of schizophrenia. If, as a significant amount of evidence shows, cannabis use contributes to the risk, or triggers schizophrenia in vulnerable individuals, then very soon, it will be accounting for 10% of all new cases of schizophrenia in Wales and Britain, with increases in schizophrenia starting earlier among young men in particular.
Researchers, in their published article in Addiction Journal, say that exposure to cannabis quadrupled in the 30 years prior to 2002. Its use in children under 18 grew 18-fold.
Some researchers suggest that if cannabis use truly triggers schizophrenia, then a rise in the number of new cases of schizophrenia should be seen. Model projections of onset of disease have been made based on heavy cannabis use, as well as on light use. According to model projections (based on historical data), by 2010 about 10% of new cases of schizophrenia could be due to heavy cannabis use. If even light use of cannabis triggers schizophrenia, then about one fourth of new cases (25%) could be due to cannabis use by 2010.
Matthew Hickman, lead author of the study, says:
"The challenge now is to improve our data on schizophrenia occurrence to see whether the projected increase occurs. This will tell us more about how important cannabis is as a cause of schizophrenia."
Thanks goes to Elda for bringing this article to our attention.
Read the full article:
Substantial increases in both prevalence and incidence of the disease are forecast by the end of the decade, with increases in schizophrenia starting earlier among young men in particular.
The research study matches historic trends in cannabis use and exposure from a national population survey against estimates of new occurrences of schizophrenia in three English cities (Nottingham, Bristol and the London Borough of Southwark).
The researchers assess what might happen to schizophrenia cases if we assume a causal link between cannabis use and onset of psychotic symptoms, an association widely recognised by some psychiatrists and researchers and considered recently by the Advisory Council on the Misuse of Drugs.
Exposure to cannabis grew fourfold over the thirty years to 2002, and its use among under-18s by 18-fold, say the researchers. If cannabis use causes schizophrenia, these increases in its use would lead to increases in overall schizophrenia incidence and prevalence of 29 per cent and 12 per cent respectively, between 1990 and 2010. (Incidence is defined as the frequency of new occurrences; and prevalence is the percentage of the population affected by the disease.)
Model projections suggest that if the association is confined to heavy cannabis users only, then approximately 10 per cent of schizophrenia cases may be due to cannabis by 2010. However, assuming an association between onset of the disease and both light and heavy users, then approximately one-quarter of new cases could be due to cannabis.
John Macleod, co-author and academic GP, said: “We need to remember that our study does not address the question whether cannabis causes schizophrenia: this remains unclear.”
Matthew Hickman, lead author of the study, added: “The challenge now is to improve our data on schizophrenia occurrence to see whether the projected increase occurs. This will tell us more about how important cannabis is as a cause of schizophrenia.”
Reference: Cannabis and schizophrenia: model projections of the impact of the rise in cannabis use on historical and future trends in schizophrenia in England and Wales (2007). Addiction 102 (4), 597-606.
Posted by Jeanie Wolfson at March 24, 2007 08:35 AM
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