Australian Clinical Psychologist ISSN 2204-4981 Volume 2  Issue 1  20103 Corresponding author: Professor Jan Copeland, NCPIC University of New South Wales E: J.Copeland@unsw.edu.au Cannabis: Use, Harms, Disorder, and Interventions Jan Copeland and Dion Alperstein National Cannabis Prevention and Information Centre (NCPIC) Medicine, University of New South Wales Abstract: Cannabis is the most common illicit drug of dependence in the Western world. Frequent cannabis use, especially when first used before the age of 16 years, is associated with addiction, poor mental health, impaired memory and learning, reduced educational attainment, in addition to social and legal difficulties. Despite the harms associated with cannabis use, dependent cannabis users are less likely to present for treatment than other illicit drug users and problematic cannabis use is rarely detected by health professionals. It is important that clinicians regularly include screening and assessment of cannabis use and account for cannabis use in case formulations. This paper will outline the prevalence of cannabis use, its associated harms, diagnostic considerations, and a brief review of best-practice treatment. Keywords: cannabis, marijuana, treatment, addiction, assessment, brief interventions Prevalence The 2013 National Drug Strategy Household Survey revealed that around 1 in 10 Australians (10.2%; or 2,000,000) aged 14 years and over, reported using cannabis in the previous 12 months and more than a third (35%; 6,600,000) had used over their lifetime (AIHW, 2014). Among recent cannabis users, 12.8% of those aged 14 years and over are daily users with an additional 19.5% using weekly or more often. The age group with the highest prevalence of recent cannabis use are 20-29 year olds with 24.7% of males in that age group reporting use (AIHW, 2014). As with tobacco, Indigenous Australians are twice as likely to smoke cannabis as non-Indigenous Australians. Cannabis use among young people is particularly concerning, with those aged 14-19 years more likely to have used cannabis than tobacco (AIHW, 2014). In the US, past year cannabis use significantly increased from 2001-2002 compared with 2012-2013 from 4.1% to 9.5% of participants in a nationally representative survey reporting use (Hasin et al., 2016). The proportion of participants reporting cannabis use disorders in the same study also doubled in that time period. Cannabis is most commonly known as marijuana in the US due to their