One of the main goals of legalizing medicinal cannabis is to eliminate black market sales, and a study out of Washington state shows that this goal could be realized. In a recently published study of public wastewater samples in a Washington state population center, cannabis use both increased and substantially shifted from the illicit market since retail sales began in 2014.
The study used wastewater samples collected at a treatment plant and analyzed for drugs and metabolites at extremely low concentrations (part per billion or part per trillion levels). The data was used to track drug consumption trends, both legal and illegal. The concentration of the metabolites can be used to “back calculate” to the actual number of doses of drug used in a particular area.
The researchers estimate that the THC-COOH (the metabolite of psychoactive THC in cannabis created within the human body) found in wastewater has increased by 9% per quarter, on average, from December 2013 to December 2016. During this time, cannabis sales increased at nearly 70% per quarter, on average, for stores operating from August 2014 to December 2016.
The intended purpose of legalizing medicinal cannabis was to eliminate black market sales. The results of this study suggest that in this population, sales changes are proportional to changes in waste water effluent metabolite measurement and that “legal sales appear to have displaced a large portion of the illicit market.”
Using wastewater-based analysis to monitor the effects of legalized retail sales on cannabis consumption in Washington State, USA. Addiction, 2019.