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Abstract
The overall aims of the current thesis were to determine the feasibility, acceptability, and efficacy of a brief motivational and cognitive-behavioural intervention in reducing cannabis use and cannabis related problems among Australian adolescent cannabis users: the Adolescent Cannabis Check-up. In addition it was intended to develop and psychometrically assess instruments to measure cannabis problems and cannabis dependence among adolescent cannabis users. The thesis is presented as a series of four related studies. Study 1 consists of an uncontrolled feasibility study of a brief (2-3 session) motivational intervention designed for adolescent cannabis users. Included in the intervention model was a separate session for concerned parents. The data analysis for this study was conducted in a pre-test post-test design and demonstrated that participation in the intervention was associated with improved outcomes. The intervention was shown to be feasible and acceptable to participants. Study 2 comprises an assessment of the psychometric performance of the Severity of Dependence Scale (SDS) in a population of adolescent cannabis users. Study 3 describes the development and psychometric testing of a novel assessment instrument designed to measure cannabis-related problems (other than dependence) among young people. Finally, Study 4 is a randomised controlled trial of the Adolescent Cannabis Check-up intervention, which builds on the feasibility study and incorporates the assessment instruments that were evaluated as valid and reliable in Studies 2 and 3. As hypothesised, significantly greater reductions in cannabis use and symptoms of cannabis dependence were found in the intervention group compared with the delayed treatment control group, which provides evidence for the efficacy of the intervention. The study presents a unique contribution to the intervention literature and demonstrates the potential to reduce the harms associated with cannabis use among young people.