HIV Insight: High-Frequency Drug Purity and Price Series as Tools For Explaining Drug Trends and Harms in Victoria, Australia

Methamphetamine-related harms in Victoria have increased recently 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.

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 during the same period. Purity-adjusted price data for methamphetamine and heroin were obtained for the period 2009-13 by combining the two data sets.

While the average purity of heroin seizures remained consistent and low, the average purity of powder and of crystal methamphetamine seizures increased from 12% to 37% and 21% to 64%, 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 to $294, powder methamphetamine did not change significantly from $252, and crystal methamphetamine increased substantially from $464 in 2009 to $795 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.

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.

Below: Average price [Melbourne Injecting Drug User Cohort Study (MIX)] and purity-adjusted price [MIX prices adjusted by average Victoria Police Forensic Services Department (VPFSD) seizure purities] per gram of heroin and methamphetamine, January 2009 to July 2013

Below: Average purity of Victoria Police Forensic Services Department (VPFSD) seizures, January 2009 to July 2013

Below: Price series and 95% confidence intervals for 1 pure gram of heroin and methamphetamine based on regressions controlling for quantity discounts, Melbourne Injecting Drug User Cohort Study (MIX) prices adjusted by Victoria Police Forensic Services Department (VPFSD) seizure purities, January 2009 to July 2013. Crystal methamphetamine series has been slightly right-shifted for clarity