The economic model of rational addiction was a breakthrough in the economic theory of consumption of addictive substances. This model’s aim is to reliably estimate an addict’s change in consumption of an addictive substance due to a change in the drug’s price or the price of another drug to which the individual is addicted. Polydrug abuse within populations of heroin addicts has been observed within health services research literature for some time. Suggestions have been made to target treatment interventions and outcome assessment to multiple drugs, rather than a single drug in clinical trials involving substance abusers. Despite this, relatively little epidemiological research has been carried out to evaluate the effectiveness of different modes of treatment for drug abuse in polydrug addicts. Bohdan Nosyk is researching whether individuals addicted to more than one substance (e.g. heroin and cocaine) display some association in their consumption patterns of these substances. If there is a significant association in consumption, focusing treatment on one addiction may be ineffective given the increase in consumption within the other (untreated) drug addiction. This study will survey individuals addicted to multiple drugs residing in Vancouver’s Downtown Eastside to determine the relationship between illicit drug prices and consumption. Research into the addicted illicit drug consumer’s behaviour – in particular, how the consumer substitutes between substances and which drugs tend to complement one another – will provide policy-makers with evidence on which to base future directions in the treatment for addictive substance abuse.