Cannabis use has both increased and substantially shifted from the illicit market since retail sales began in 2014 in Washington state, report researchers.

The researchers analyzed wastewater samples from 2013-2016 from two treatment plants that service a community of 200,000 in Western Washington.

“We set out to perform a wastewater-based analysis that explored the impact of newly legalized retail cannabis sales on its use, and to determine if this approach could estimate the size of the legal market place,” says Dan Burgard, who chairs the chemistry department at the University of Puget Sound.

Tracking marijuana use

The researchers estimate that THC-COOH (the metabolite of psychoactive THC in cannabis created within the human body) in wastewater has increased by 9 percent per quarter, on average, from December 2013 to December 2016. During this time, cannabis sales increased at nearly 70 percent per quarter, on average, for stores operating from August 2014 to December 2016.

“Given that wastewater represents a total population measure, these findings suggest that many established users switched very quickly from the illegal to the legal market,” says Burgard. “This is the strongest statement possible regarding displacement of the illegal market.”

“This project was designed to aid the understanding of how the sales of adult recreational cannabis impact its total consumption within a population,” says coauthor Caleb Banta-Green, interim director and principal research scientist at University of Washington’s Alcohol and Drug Abuse Institute.

“We believe this will be a valuable tool for local, state, national, and international policy makers as they assess and consider Washington’s recreational cannabis law.”

Growing legalization

In the past six years, nine US states (Colorado, Washington, Alaska, Oregon, Nevada, California, Maine, Massachusetts, Vermont, Michigan, and the District of Columbia), as well as the countries of Uruguay and recently Canada, have legalized the adult use of recreational cannabis.

“Existing measures, particularly surveys are subject to important biases and limitations, including potential changes in self-report as social norms change as well as very limited information on the amount of THC actually consumed,” Banta-Green notes. “Wastewater based estimates help address these limitations.”

The researchers note that their findings suggest that legalization is, in part, achieving one of its primary objectives which was to eliminate black market sales.

The research process included testing samples from 387 days spread over three years. The team utilized a new method that enables a complementary and potentially more timely and objective assessment of illicit drug consumption compared to existing measures.

Raw wastewater samples representing a full day are collected at a treatment plant and analyzed for drugs and their metabolites at extremely low concentrations (part per billion or part per trillion levels). These data can be used to track drug consumption trends, both legal and illegal, but not individual users. In some instances, 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 report appears in the journal Addiction. Funding for the research came, in part, from a grant from the National Institute on Drug Abuse.

Source: University of Washington

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