This chapter presents the main tools aiming to screen different kinds of cannabis use and problems resulting from it. It is not an exhaustive presentation of the published literature, yet it provides concise discussion of the concepts and tests developed so far.
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There is evidence that cannabis use sometimes leads to problems, and these problems are now a major concern in the field of public health. As a consequence, many surveys try to evaluate the proportion of cannabis users who suffer problems resulting from cannabis use or the proportion of dependent users. The largest recent surveys were conducted in the USA and Australia. Estimations vary and depend on the instruments used. In Australia, the National Survey of Mental Health and Well-being conducted a study in 1997 among a representative sample of 10 600 people of the Australian population aged 18 and over, and used DSM-IV and ICD-10 diagnoses. Swift et al.
(2001) found that 1.5 % (DSM-IV) or 1.7 % (ICD-10) of this population was cannabis dependent, with marked differences in symptom prevalence. The proportions among cannabis users during the last 12 months were 21 % (DSM-IV) and 22 % for ICD-10. In the USA, according to a recent NHSDA survey (SAMHSA, 2002), 2 % of people aged 12 and over fulfilled DSM-IV criteria for cannabis dependence or abuse during the last 12 months. The proportion among those aged 18–25 years was 6 %. According to this survey, 17 % of last year cannabis users fulfilled criteria for cannabis dependence or abuse.
The concepts and definitions used in the DSM and in the ICD are controversial, and not all studies support the idea that cannabis smokers develop dependence as well as abuse (see also Witton, this monograph, Vol. 2). In a study by Hollister (1986), for instance, cannabis was given to subjects for a certain period of time in order to study the effects of interruption of the supply. The first attempts failed, but this may be due to amounts of cannabis, which were too small, and a period of supply, which was too short, for ethical reasons. Many authors do, however, confirm that dependence can occur with long-term use: patients who receive significant doses over a long period of time develop symptoms such as occasional perspiration, slight nausea, anxiety and sleeplessness (Compton et al., 1990; Jones, 1996; Crowley et al., 1998; Haney et al., 1999a,b; Vandrey et al., 2005). Despite this general agreement, Jones (1996) emphasises that frequency of dosing and dose interval are more important than daily dose for producing a cannabis withdrawal syndrome. Typical patterns of cannabis use appear to be non-optimal conditions to get an obvious withdrawal syndrome, though less obvious symptoms may be relevant when treating cannabis-dependent patients. Smith (2002) points out that these symptoms are not specific for cannabis (they can be observed with tobacco) and vary with the psychological profile of the individual. Coffey et al. (2002), argue that tolerance might be useless in clinical assessment of cannabis dependence.
The list of criteria used for psychological dependence for all drugs in the DSM-IV definition of dependence appears non-exhaustive. In addition, some of these criteria have been criticised for not seeming relevant for certain researchers (Soellner, 2002).
For example, criterion 7, dealing with the continuation of use despite the recognition of its contributing role to some psychic or physical problems, ignores the eventuality that the user might have no intention of stopping use and, on the contrary, might rationally
Chapter 2
43 choose to continue to use it because it provides greater benefits. This possibility has not been investigated. Indeed, the challenge of adapting a generic mental health standard, such as IV, to use of a specific drug is illustrated in the discrepancy between DSM-IV’s definition of dependence for all drugs and the criteria it proposes for cannabis.
Problems with conceptualising harmful use and thresholds are compounded by the difficulties of developing the screening tools themselves. Measures such as MINI use items from the ‘problem domain’ and refer to them as criteria of dependence. It also seems problematic to define dependence by its consequences, for example criterion 6 in the DSM-IV. As the definition of dependence is so strictly delimited in DSM, a link between dependence and its potential consequences cannot be proven (Soellner, 2002).
‘Drift’ in the use of items from the problem domain can also be criticised as these items do not measure whether users intend to quit. Intention to quit is crucial, as research shows that cannabis users argue that they would and could quit if cannabis consumption led to suffering (Swift et al., 1998), and cannabis use is not necessarily viewed as a problem by dependent users.
Other variables are also problematic. Some of the dependence criteria, such as spending a great deal of time around the substance, might be confounded by the illegality of the drug (this is a problem for MINI and ICD-10, for instance). In CUDIT and CAGE there is a question about feelings of guilt after using cannabis, which could also be confounded by the illegality of the drug. Thus, most screening measures combine the dimensions of psychological dependence and harm. This is true of CUDIT, MINI and CAST, and thus it is not clear what they are screening for: dependence? Or abuse?
These are concepts that DSM-IV makes a serious attempt to separate, and combining the two areas is problematic for an illicit substance: many of the problems have resulted from the fact that cannabis is illegal.
In general, analysis of diagnostic tools, such as DSM-III, DSM-IV and ICD, used as severity scales for drug dependence shows that diagnostic algorithms greatly influence the results (Langenbucher et al., 1995). A comparison between DSM-III R and DSM-IV emphasises the influence of the evolution of the diagnostic criteria on the screening results (Mikulich et al., 2001). These problems question the very nature of the concepts of addiction: what should be measured, why and how?
An examination of concepts used in American and European definitions of the stages of drug use disorders reveals some cultural differences. For example, the definition of drug abuse, according to the American DSM-IV, contains moral criteria and characteristics, either in the concepts themselves or in the wording of the concepts, whereas the European definition of harmful use, according to the ICD-10, seems more pragmatic.
Law transgression or failing in social roles are included in DSM-IV’s definition of abuse, in addition to using despite knowledge that damage results from use. Use in hazardous
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situations, such as driving, may be seen as risky behaviour that increases risk of being injured or of causing injury, yet an accident may never occur. In DSM-IV’s definition of dependence, criterion 7 presupposes that use itself is bad, even if it brings a benefit and contributes to the psychological balance of the user, who might have made a rational decision to continue using. In a sense, the user under DSM-IV is presupposed to have a social duty and responsibility: he or she must conform to social and legal norms. Users’
knowledge of the law and their psychological reaction both contribute to the definition of abuse. Such moral rationale seems less present in ICD-10’s definition of harmful use, although these concepts should perhaps be examined when defining drug-related harm.