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PhD Thesis - Swift, W

Patterns and correlates of cannabis dependence
Swift W (1999)

Abstract:
The sequelae of long-term cannabis use, including the prevalence and nature of cannabis dependence, are poorly understood. This thesis investigated the applicability of the influential drug dependence syndrome (DDS) concept to cannabis. Given the proposed plasticity of the DDS, its manifestation was examined among one clinical sample and two non-clinical samples of long-term users in urban and rural New South Wales. Several operationalisations of dependence criteria, including structured diagnostic interviews, examined the impact of measurement issues on the prevalence, nature and correlates of cannabis dependence.

This thesis demonstrated that long-term cannabis users readily reported symptoms consistent with those postulated for the DDS. Although substantial proportions qualified for DSM-III-R, DSM-IV and ICD-10 cannabis dependence diagnoses, the prevalence and manifestation of dependence varied between samples and with the way in which the DDS was assessed. The rural sample were least likely to meet dependence criteria, despite the most extensive use history. The urban clinical sample were almost universally dependent. Prevalence was intermediate in the non-clinical urban sample, among whom it remained stable over a one year follow-up period. Users in the non-clinical samples who met dependence criteria typically displayed little concern over their use.

There was poor to moderate concordance between dependence diagnoses in the non-clinical samples, with greater agreement among the more severely dependent clinical group. Age was most consistently associated with severity of cannabis dependence. These data largely failed to support the hypothesis that cannabis dependence symptoms form a single, coherent underlying dimension. Principal components analyses suggested a more diffuse syndrome which did not conform to that frequently identified for substances such as alcohol and opiates.

This thesis provided mixed evidence for the applicability of the DDS to cannabis. Although long-term users commonly reported symptoms of dependence measured by current diagnostic criteria, they did not form a coherent syndrome in the way that symptoms of alcohol or opiate dependence do. These findings also indicated that the operationalisation of dependence symptoms and the context of cannabis use can influence the measurement, prevalence and understanding of dependence.

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