The dynamics of methadone treatment for intravenous opioid users. The major flows in this study were people cycling between being on methadone and off treatment. This is a minimal model of the insights from the more detailed modelling project described in Chalmers J, Ritter A, Heffernan M, McDonnell G. Modelling pharmacotherapy maintenance in Australia. A report prepared for the Australian National Council on Drugs. Sydney: Drug Policy Modelling Program, University of New South Wales; 2009