Illicit drug use creates significant burden at societal, family and personal levels. Every year substantial resources are allocated for treatment and the consequences of illicit drug use in Australia and around the world. Heroin is one of the major forms of illicit drugs. Several independent heroin treatment strategies or interventions exist and state-of-the art research demonstrates their efficacy and relative cost-effectiveness. However, assessing total potential gains and burden from providing all treatment interventions or varying the mix of heroin treatments has never been attempted. This paper proposed an individual-level simulation model (ISM)which addresses net social benefit over a lifetime that can accommodate the complexity of individuals going in and out of multiple treatments and their corresponding costs and benefits arising from different treatments during the life-course of heroin users in the context of New South Wales (NSW)Australia. This model is intended to serve as an effective tool for economic evaluation and policy making in the illicit drug area in Australia. The validity of the model has been assessed by comparing short term outcomes or examining the status of participants at a various points of time predicted from the model with other data sets that were not used to parameterise the model. Initial model results have been also presented to highlight different types of scenario analysis that can be conducted in future.