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Researchers from the University have found evidence which contradicts previous governments' assertions on the effects of the reclassification of cannabis.
The argument for an evidence-based drugs policy was something which came under scrutiny at the University earlier this year when a motion for YUSU to lobby for such legislation was passed by students. The results appear to lend weight to this argument, originally put forward by the University of York Liberal Democrat Society.
The researchers have found that rather than leading to a decrease in admissions for cannabis psychosis, the change in cannabis declassification in 2009 coincided with a significant increase in hospital admissions for the problem.
The Misuse of Drugs Act Cannabis originally assigned the drug to Group B, but in 2004, it was transferred to Group C.
However in 2009, due to concerns about a possible link between stronger varieties of the drug and schizophrenia, the change in classification was reversed.
Researchers from the University's Department of Health Sciences examined admissions to psychiatric hospitals in England between 1999 and 2010 to explore whether reclassifications coincided with changes in the admissions rate for cannabis psychosis.
The results revealed that there was an increasing trend in admissions from 1999 to 2004, but after the reclassification of cannabis from class B to C in 2004, there was a decline until the next reclassification in 2009.
Following the reversal back to class B in 2009, there was a significant increase in admissions.
According to the authors of the study, published in the International Journal of Drug Policy: "The association is unlikely to be due to changes in cannabis use over this period, but possible explanations include changes in policing and systematic changes in mental health services unrelated to classification decisions."
The study was led by Ian Hamilton from the Department of Health Sciences, who is an expert on the relationship between substance misuse and mental health.
Psychosis describes a range of symptoms, such as distortions of reality, hearing voices, difficulty in thinking and problems with motivation.
Hamilton commented on the results: "Our research shows an interesting relationship between the Government's decision to reclassify cannabis and the rate of hospital admissions for cannabis psychosis. It is significant as the Government's argument for reclassification was made on the basis that the stronger forms of cannabis known as 'skunk' are more likely to lead to mental health problems such as psychosis. However, our research challenges this."
He added: "While our study shows a statistical association between the reclassification of cannabis and hospital admissions for cannabis psychosis, it is in the opposite direction to that predicated by the presumed relationship between the two."