The BBC took a step forward this week producing a balanced review of the literature on cannabis for the first time in about a decade. There are however two myths about cannabis that the documentary fails to really break down.
1. Cannabis Causes Schizophrenia
Schizophrenia rates have been at a plateau for the last 100 years (consistently affecting about half a percentage point of the population). The majority of schizophrenics have never used cannabis in their life. Schizophrenia appears to be a genetic disorder, passing down family lines. In the past thirty years cannabis use has exploded, rising between ten and twenty fold (in the US now overtaking cigarette use in young people). In the same period of time the government has restricted the market resulting in a boom in skunk production over the past decade. With both of these two factors, if the hypothesis that cannabis causes schizophrenia were true we would expect to see a rise in schizophrenia. This did not happen, in fact there is some evidence schizophrenia is in decline. Therefore it appears clear there is no direct causal link between cannabis and schizophrenia. For a reference point, in the same period alcohol use has doubled and liver disease has risen two fold becoming the only form of “death” that is on the rise by any great degree.
Growth in Liver Disease Correlates Perfectly with Growth of Alcohol Consumption
This does beg the question of why there is a slight correlation between people with schizophrenia and cannabis use. It is starting to look more likely that cannabis is used by people with schizophrenia attempting to self medicate. One component of cannabis (CBD) has even been found to be an effective anti-psychotic. Ironically, this is the component that is lost when growers are forced to farm intensively indoors (i.e. in skunk). The evidence is certainly clear however that the main component in skunk varieties (THC) has a negative effect on those with schizophrenia, however schizophrenics are still attracted to skunk because of it’s anxiety relieving properties. The conclusion of the BBC program that it is safest to stick to strains with balanced levels of CBD/THC such as Thai Stick and avoid if your family has a history of mental illness certainly seems to be correct.
*For the record, 90% of schizophrenics smoke cigarettes for the same reasons. No one however is suggesting cigarettes cause schizophrenia.
2. Cannabis is Addictive
To it’s credit, the program does note that cannabis is not physically addictive and there are no physical withdrawal symptoms. However it naively states that “treatment rates for cannabis are on the rise” failing to recognise the proportion of those in treatment forced to attend “rehab” centres by court order instead of going to jail for possession/dealing. This is really not a fair measure of harm. I’ve been unable to uncover rehab admission statistics broken down by mode of admission, the NHS stats leave that key component out (if anyone has access please do send). It seems pretty inappropriate to force cannabis users to attend these classes when there are endless waiting lists for serious drug addicts.
Other than those two points the program was fair and balanced and I’d recommend it. In other news, across the pond the US National Institute of Drug Abuse (NIDA) has just started claiming cannabis use causes testicular cancer based on one tiny study that really showed no such thing. Sigh.
Hickman M, Vickerman P, Macleod J, Kirkbride J, & Jones PB (2007). 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. Addiction (Abingdon, England), 102 (4), 597-606 PMID: 17362293
Zuardi, A., Crippa, J., Hallak, J., Moreira, F., & Guimarães, F. (2006). Cannabidiol, a Cannabis sativa constituent, as an antipsychotic drug Brazilian Journal of Medical and Biological Research, 39 (4) DOI: 10.1590/S0100-879X2006000400001
GREEN, B. (2005). Cannabis use and misuse prevalence among people with psychosis The British Journal of Psychiatry, 187 (4), 306-313 DOI: 10.1192/bjp.187.4.306
Cattapan-Ludewig K, Ludewig S, Jaquenoud Sirot E, Etzensberger M, & Hasler F (2005). [Why do schizophrenic patients smoke?]. Der Nervenarzt, 76 (3), 287-94 PMID: 15448920
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