The Illicit Drug Reporting System (IDRS) is Australia’s federally funded national drug monitoring system. The purpose of the IDRS is to provide a standardised, comparable approach to the monitoring of data relating to the use of opiates, cocaine, methamphetamine and cannabis. The IDRS is intended to act as a strategic early warning system, identifying emerging drug problems of national concern. It is not intended to describe phenomena in detail, but rather, is designed to indicate the need for more detailed data collection by providing sensitive and timely data on emerging trends in illicit drug markets. One component of the IDRS involves interviews with regular IDU to obtain information on use patterns and drug markets. IDU are recruited as a sentinel group of users that are active in illicit drug markets. The information from the IDU survey is therefore not representative of illicit drug use in the general population, nor is it indicative of all illicit or injecting drug users, but identifies emerging trends that require further monitoring.