AIMS: Methamphetamine related harms in Victoria have recently increased, in the context of stable or declining use prevalence. We determine how changes in price and purity of methamphetamine compared to other drugs such as heroin may, in part, explain these divergent patterns. METHODS: Detailed methamphetamine and heroin purchase price data from 2152 participant interviews from the Melbourne Injecting Drug User cohort study were used to generate drug price series for the period January 2009 - June 2013. Data on drug purity from 8818 seizures made within Victoria were used to generate drug purity series over the same period. Purity-adjusted price data for methamphetamine and heroin were obtained for the period 2009-2013 by combining the two datasets. RESULTS: While the average purity of heroin seizures remained consistent and low, the average purity of powder and of crystal methamphetamine seizures increased from 12% (95%CI 10-14%) to 37% (20-54%) and 21% (95%CI 18-23%) to 64% (60-68%) respectively. Crystal methamphetamine purity was bimodal, with observations generally less than 20% or greater than 70%. The average unadjusted price per gram for heroin decreased from $374 (95%CI $367-381) to $294 ($280-308), powder methamphetamine didn’t change significantly from $252 (95%CI $233-271), and crystal methamphetamine increased substantially from $464 (95%CI $416-511) in 2009 to $795 ($737-853) in 2011. This increase was offset by an even greater increase in purity, meaning the average purity-adjusted price per gram declined. Furthermore, pure prices of both methamphetamine forms were similar, whereas their unadjusted prices were not. The pure price of heroin fluctuated with no ongoing trends. CONCLUSIONS: Decreases in methamphetamine purity-adjusted price along with the bimodality of crystal methamphetamine purity may account for some of the recent increase in methamphetamine related harm. For a given amount spent, methamphetamine purchase power has increased and the presence of extreme purity variations may challenge individuals' control of consumption.
The Melbourne Injecting Drug User Cohort Study is funded by the National Health and Medical Research Council (NHMRC, Grant number 398500). The research reported in this paper has been funded by the National Drug Law Enforcement Research Fund. PD is the recipient of an Australian Research Council Future Fellowship. AR is a recipient of an NHMRC Research Fellowship