Commentary on ter Laak <i>et al</i> .: The importance of drug market information and differentiating drug use patterns

Integrating large scale wastewater analysis with supporting data on drug prices and purity can deliver good estimates of the market size of illicit drugs. The understanding of drug use patterns also helps achieve better estimation outcomes. Wastewater analysis has been used to monitor spatial and temporal trends of drug use in communities for more than a decade now [1], but the data needs to be integrated to inform law enforcement and health policy. Ter Laak et al.’s study [2] provides a comprehensive analysis of drug market size and user behavioural differences in relation to urbanity, offering valuable insights for relevant stakeholders. Two key aspects of this study stand out: the critical role of drug market information for the interpretation of market size/prevalence, and the difference of use patterns among the three target drugs, which has the potential to indicate the nature of drug use. The data presented on drug prices and purity levels are essential for understanding a national drug market and the broad context of drug use. Variations in street drug purity can influence the levels of drugs measured in wastewater. Therefore, it is important to evaluate trends in purity data and adjust, when necessary, particularly when examining temporal and spatial patterns of population drug use, with substantially varying levels of purity [3, 4]. The study by Ter Laak et al. [2] is a good example of how purity data can be used to estimate market size and reduce uncertainties. The consistency in the purity and price of drugs serves as an indicator of the stability of the Dutch drug market. Triangulation of wastewater data with drug prices and purity may provide a better reflection of changes (or the lack thereof) in the drug market because of any intervention including shifts in manufacturing practices or the introduction of adulterants [5-8] that could lead to change in the mass of target drugs measured in wastewater. Ter Laak et al. [2] also evaluate the association of drug use with the level of urbanity. The positive relationship between urbanity and drug loads of benzoylecgonine and 3,4-methyl​enedioxy​methamphetamine (MDMA) was used to extrapolate the drug consumption estimates in all towns in the Netherlands based on their urbanity index. The variation in drug consumption throughout the week has not been discussed, but could be used to explain the observed relationship between the levels of drug consumption and the urbanity score. Both MDMA and cocaine are party drugs and have large weekday-weekend variation [9]. Sites that have a high urbanity score are more likely to contain a higher percentage of nightlife venues (pubs and clubs) compared to sites with a lower urbanity score, and therefore, have higher levels of party related drugs. Amphetamine shows no correlation with urbanity (so possibly not a party drug) and is, therefore, more regularly used. By assessing the weekly variation of the data, the authors could differentiate the nature of drug use per catchment (i.e. regular users and those who use drugs recreationally in social or party settings). Such information could help the management of drug use and support preventative measures [10]. As highlighted in a background paper commissioned by the European Monitoring Centre for Drugs and Drugs Addiction [11], integrating data on drug purity and pricing is crucial for wastewater-based epidemiology approach to accurately estimating market sizes. The current lack of up-to-date and representative data creates significant challenges, with current limitations being lack of spatial specificity, data acquisition delays and infrequent reporting. Setting up proper sampling and reporting strategies across countries can help address these limitations and improve the reliability of market size estimates. Rory Verhagen: Writing—original draft; writing—review and editing. Phong K. Thai: Conceptualization; supervision; writing—review and editing. The Queensland Alliance for Environmental Health Sciences, The University of Queensland, gratefully acknowledges the financial support of Queensland Health, Australia. None.