The results show that macro-level disruptions to drug supply had a limited impact on street-level market dynamics when there was a ready replacement drug. By contrast, street-level police interventions were shown to vary in their capacity to alter drug market dynamics. Importantly, the work’s laboratory abstraction of problem-orientated policing was shown to be the optimal strategy to disrupt street-level injecting-drug markets, reduce crimes, and minimize harm, regardless of the type of drug being supplied to the market. The paper sought to examine how street-level drug markets adapted to a macro-level disruption to the supply of heroin, under three experimental conditions of street-level drug law enforcement: random patrol, hot-spot policing, and problem-orientated policing. It utilized an agent-based model to explore the relative impact of abstractions of these three law enforcement strategies after simulating an ‘external shock’ to the supply of heroin to the street-level drug market. The findings were derived from 3 years of data, which include the period of the ‘heroin drought’ in Melbourne, Australia that commenced in late 2000 and early 2001, to measure changes in a selected range of crime and harm indicators under the three policing conditions. Tables, figures, references