Patterns of co-morbidity between alcohol use and other substance use in the Australian population LOUISA DEGENHARDT & WAYNE HALL National Drug and Alcohol Research Centre, University of New South Wales, Sydney, NSW, Australia Abstract The present study describes patterns of co-morbidity between alcohol use and other substance use problems in the Australian population using data from the 1997 National Survey of Mental Health and Well-Being. Multiple regression analyses examined whether the observed associations between alcohol and other drug use disorders were explained by other variables, including demographic characteristics and neuroticism. We also assessed whether the presence of co-morbid substance use disorders affected treatment seeking for a mental health problem. Alcohol use was related strongly to the use of other substances. Those who did not report alcohol use within the past 12 months were less likely to report using tobacco, cannabis, sedatives, stimulants or opiates. Higher rates again were observed among those with alcohol use disorders: half (51%) of those who were alcohol-dependent were regular tobacco smokers, one-third had used cannabis (32%); 15% reported other drug use; 15% met criteria for a cannabis use disorder and 7% met criteria for another drug use disorder. These associations were not accounted for by the demographic and other variables considered here. Co-morbid substance use disorders (sedatives, stimulants or opioids) predicted a high likelihood of seeking treatment for a mental health problem among alcohol-dependent people. [Degenhardt L, Hall W. Patterns of co-morbidity between alcohol use and other substance use in the Australian population. Drug Alcohol Rev 2003;22:7 – 13] Key words: alcohol, co-morbidity, drugs, drug use disorders, epidemiology. Introduction Alcohol is one of the most commonly used psychoactive substances in the Western world. In 1998, the Australian National Drug Strategy Household Survey estimated that around nine in 10 people aged 14 years and over had used alcohol at some point in their lives and 83% had done so in the past year [1]. In 1997, the Australian Bureau of Statistics (ABS) conducted the National Survey of Mental Health and Well-Being, the first Australian population survey of the prevalence of mental disorders and assessed DSM-IV alcohol and other drug use disorders (abuse and dependence). DSM-IV substance abuse criteria re- quired a pattern of substance use that is causing clinically significant distress or impairment [2]. DSM- IV substance dependence criteria required a cluster of three or more indicators that a person continues to use the substance despite significant substance-related problems [2]. Previous US epidemiological research has suggested that alcohol use is associated with other substance use. US surveys have found an association between daily cigarette smoking and alcohol use [3]. The US Epidemiological Catchment Area (ECA) study found that those with lifetime alcohol abuse/dependence were significantly more likely to have used other drugs, and to meet criteria for another drug use disorder [4]. Just over one in five people (22%) meeting lifetime criteria for alcohol abuse or dependence also met criteria for another drug use disorder, with the majority of such people meeting criteria for a cannabis use disorder [4]. Similar results were also found in the US National Co- morbidity Survey (NCS) [5]. However, there has been no previous examination of co-morbidity between alcohol use disorders and other substance use disorders in the Australian population. Several factors are consistently related to alcohol use disorders and other substance use disorders, which may explain this pattern of co-occurrence or co-morbidity Received 11 August 2001; accepted for publication 2 October 2002. Louisa Degenhardt PhD, Acting Lecturer, National Drug and Alcohol Research Centre (NDARC), University of New South Wales, Sydney, Australia; Professor Wayne Hall, Visiting Professor, National Drug and Alcohol Research Centre (NDARC), University of New South Wales, Sydney, Australia. Correspondence to Dr Louisa Degenhardt, National Drug and Alcohol Research Centre (NDARC), University of New South Wales, 22 – 32 King Street, Randwick, NSW, 2031, Australia. Drug and Alcohol Review (2003), 22, 7 – 13 ISSN 0959-5236 print/ISSN 1465-3362 online/03/010007–07 # Australian Professional Society on Alcohol and Other Drugs DOI: 10.1080/0959523021000059776