Research paper
Effect of reclassification of cannabis on hospital admissions for cannabis psychosis: A time series analysis

https://doi.org/10.1016/j.drugpo.2013.05.016Get rights and content

Abstract

Background

The UK Misuse of Drugs Act (1971) divided controlled drugs into three groups A, B and C, with descending criminal sanctions attached to each class. Cannabis was originally assigned by the Act to Group B but in 2004, it was transferred to the lowest risk group, Group C. Then in 2009, on the basis of increasing concerns about a link between high strength cannabis and schizophrenia, it was moved back to Group B. The aim of this study is to test the assumption that changes in classification lead to changes in levels of psychosis. In particular, it explores whether the two changes in 2004 and 2009 were associated with changes in the numbers of people admitted for cannabis psychosis.

Method

An interrupted time series was used to investigate the relationship between the two changes in cannabis classification and their impact on hospital admissions for cannabis psychosis. Reflecting the two policy changes, two interruptions to the time series were made. Hospital Episode Statistics admissions data was analysed covering the period 1999 through to 2010.

Results

There was a significantly increasing trend in cannabis psychosis admissions from 1999 to 2004. However, following the reclassification of cannabis from B to C in 2004, there was a significant change in the trend such that cannabis psychosis admissions declined to 2009. Following the second reclassification of cannabis back to class B in 2009, there was a significant change to increasing admissions.

Conclusion

This study shows a statistical association between the reclassification of cannabis and hospital admissions for cannabis psychosis in the opposite direction to that predicted by the presumed relationship between the two. However, the reasons for this statistical association are unclear. It is unlikely to be due to changes in cannabis use over this period. Other possible explanations include changes in policing and systemic changes in mental health services unrelated to classification decisions.

Introduction

Of all areas of British drug policy over the past fifteen years, it has been cannabis that has most often seized the spotlight. Since the report of the Independent Inquiry into the Misuse of Drugs Act in 2000, there has been considerable media coverage of the question of legal classification, focused increasingly in recent years on the association between cannabis and schizophrenia and linked concerns about stronger strains of cannabis or ‘skunk’. Analysis of seized samples in the USA, UK and a number of other European countries have shown some increase in the strength of cannabis as measured by tetrahyrocannabinol (THC) content (Cascini et al., 2012, McLaren et al., 2008, Mehmedic et al., 2010). This has led to increased interest in the question of how cannabis use and supply is controlled and, in the UK, in the issue of the drug's classification. The UK Misuse of Drugs Act (1971) divided controlled drugs into three groups A, B and C, with descending criminal sanctions attached to each class. In January 2009, cannabis was upgraded from Class C to Class B at least in part, because of concerns about the links with schizophrenia.

This paper analyses trend data in monthly admissions for cannabis psychosis to explore whether the changes in the classification of cannabis in the UK were associated with the number of hospital presentations for the treatment of cannabis psychosis.

Cannabis first became a controlled drug in the UK when the 1925 Dangerous Drugs Act was enacted in 1928. This and other drug legislation was then rationalised in 1971, with the passing of the 1971 Misuse of Drugs Act. This act provided a hierarchical system by which the controlled drugs were classified, with those drugs deemed most dangerous being placed in Class A through to those deemed least dangerous in Class C. When the Act was enacted in 1971, cannabis was placed in Class B. However, in January 2004, it was moved from Class B to C and then in January 2009 it was moved back to Class B.

The initial reclassification to Class C was championed by the then UK Home Secretary, David Blunkett. In his evidence to the Home Affairs Select Committee (HASC) inquiry into the Government's 10-year drug strategy on 23 October 2001, he gave three main reasons for the change: liberating police time for policing Class A drugs, protecting the ‘credibility’ of drug education (in that the drug classes needed to reflect the actual harms caused by drugs, otherwise the credibility of all drug information would be undermined) and greater ‘clarity’ and ‘coherence’ (Lloyd, 2008a). In early 2002, both the HASC and the body of experts advising the UK Government on policy issues, the Advisory Council on the Misuse of Drugs, recommended that cannabis be reclassified. However, by late January 2004, when a Misuse of Drugs Act Modification Order was brought into effect the change, the public mood had altered, with widespread negative press reports suggesting that Blunkett had ‘made a hash of it’ (Warburton, May, & Hough, 2005).

The changes brought about in January 2004 were complicated by the simultaneous enactment of the Criminal Justice Act 2003, which introduced amendments to the Police and Criminal Evidence Act of 1984 making possession of cannabis (but no other Class C drug) an arrestable offence. It also increased the maximum sentence for all Class C trafficking and supply offences from 5 to 14 years – the same maximum for Class B offences. This effectively rendered the legal difference between cannabis as a Class C drug and cannabis as a Class B drug insignificant, although this was poorly understood by the media and presumably, the wider public (Lloyd, 2008b). However, the move to Class C did affect policing. Before the introduction of the new legislation in 2004, the Association of Chief Police Officers (ACPO) introduced guidance on which aggravating factors would warrant an arrest for cannabis possession and in which circumstances police officers should give a ‘street warning’ – a formal, on-the-spot warning (ACPO, 2003). An evaluation of these changes concluded that ‘Overall our findings suggest that the reclassification of cannabis…has had a smaller impact than advocates of the change hoped and than opponents feared’ (May, Duffy, Warburton, & Hough, 2007, p. 44).

A new concern in many of the media reports from 2004 onwards, was the mental health effects of smoking cannabis – in particular the association with psychosis (Lloyd, 2008a). Psychosis is a term that describes a range of symptoms, for example: distortions of reality, hearing voices, difficulty in thinking and problems with motivation (Turkingdon & Weiden, 2009). Media concerns have particularly focused on the stronger varieties of cannabis, and their role in cannabis induced psychosis: ‘sensimilla’ or ‘skunk’ has higher Δ-9-tetrahydrocannabinol (THC) and lower cannabidiol (CBD) than cannabis resin, both of which may be associated with psychosis (ACMD, 2008, Weissenborn and Nutt, 2012). Reflecting these concerns, the Advisory Council on the Misuse of Drugs (ACMD) was twice asked in the space of three years, by the Home Secretaries at the time, to consider the evidence in this area. Its two resulting reports in 2005 and 2008 both reaffirmed that cannabis should remain in Class C (ACMD, 2005, ACMD, 2008). However, ignoring these recommendations, the Home Secretary Jacquie Smith announced in May 2008 that she would be moving cannabis back to Class B, stating that:

There is accumulating evidence, reflected in the Advisory Council on the Misuse of Drugs report, showing that the use of stronger cannabis may increase the harm to mental health. Some young people may be ‘binge smoking’ to achieve maximum possible intoxication which may be very serious to their mental health.

Thus, fears about the mental health harms associated with cannabis became the rationale for the cannabis reclassification decision. This paper will explore whether there is an association between the two, as measured by admissions to psychiatric hospitals in England.

Section snippets

Methods

Records of admissions for cannabis psychosis in National Health Service Hospitals in England, were extracted from the Hospital Episodes Statistics (HES) database for the period between April 1999 and December 2010. Records of a diagnosis of psychosis due to use of cannabis consisted of nine ICD-10 diagnostic categories, F12.0–F12.5, F12.7–F12.9 (World Health Organisation, 2010). Patients with a secondary diagnosis of cannabis psychosis were excluded. Similar monthly admission data for all

Cannabis psychosis admissions

Fig. 1 and Table 1 show the trends in admissions and the results of the time series analysis. From 1999 up to the first reclassification in 2004, there was a significantly increasing mean number of monthly admissions for cannabis psychosis (p < 0.0001). There was little or no evidence of an immediate level change after the first (p = 0.10) or second (p = 0.99) reclassification. However, there were significant changes in the month-to-month trend in the mean number of admissions after the first (p < 

Discussion

This study appears to suggest that there may be an association between the reclassification of cannabis and hospital admissions for cannabis psychosis: although in the opposite direction to that envisaged by Jacquie Smith's reasoning for moving cannabis to Class B in 2009. There was a significant, declining trend in admissions following the shift from Class B to C in 2004, suggesting that reducing the classification of cannabis does not result in an increase in serious mental health problems

Limitations of the study

There are several limitations to the research. No independent check of the primary data could be undertaken; it is therefore difficult to estimate the error that it contains. Areas where error could occur include fidelity to diagnostic criteria which is a particular issue for the diagnosis of cannabis psychosis. Although guidance is offered in the main classification indices, as Baldacchino, Hughes, and Kehoe (2012) observes “…a distinctive cannabis psychopathology that is clearly

Conclusion

This study has shown a surprising relationship between cannabis classification and admissions for cannabis psychosis: a relationship that is antithetical to that assumed by the decision to move cannabis to Class B in 2009. Explaining why this should be the case is a considerable challenge and we suspect that the pronounced changes in admission trends that we have found are likely to be driven by causal factors other than changes in classification. Nevertheless, there is the potential for mental

Conflict of interest

No conflict of interest.

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