"Alcohol remains the most common principal drug of concern, increasing over time to 46% of all treatment episodes in 2008–09 compared with 38% in 2002–03. Treatment for heroin use has been declining over time ....Treatment for cannabis use has remained stable ....while amphetamine treatment as a proportion of all episodes has declined .....A multitude of factors may potentially contribute to changes in the pattern of drugs for which treatment is sought over time. These factors include but are not limited to changes in the drug market, the perception of use by drug users and the community, the availability of treatment services and willingness to seek treatment."

Reference: Australian Institute of Health and Welfare 2010. Alcohol and other drug treatment services in Australia 2008–09: report on the National Minimum Data Set. Drug treatment series no. 10. Cat. no. HSE 92. Canberra: AIHW

http://www.aihw.gov.au/publications/index.cfm/title/11500