Our paper examines how street-level drug markets adapt 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. We utilize 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. We use 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. Our results show that macro-level disruptions to drug supply have a limited impact on street-level market dynamics when there is a ready replacement drug. By contrast, street-level police interventions are shown to vary in their capacity to alter drug market dynamics. Importantly, our laboratory abstraction of problem-orientated policing is 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.