Detected levels of cannabis metabolites, combined with cannabis sales records, show that legal weed is winning in Washington state.
A team of researchers from the University of Puget Sound and the University of Washington recently took to the sewers to find out just how people's cannabis habits have changed since Washington legalized recreational cannabis in 2014. By testing sewer water for THC-COOH—a metabolite that people expel after consuming cannabis—the researchers could get a pretty good idea of how much cannabis was being consumed in the area.
Sewage samples collected between the summer of 2014 and winter 2016 found that cannabis consumption in Washington increased by about nine percent each quarter. The fact that more people are consuming cannabis post-legalization perhaps isn't surprising, and the increased consumption rate really isn't that high. However, during the same period legal cannabis sales increased by between 60 and 70 percent each quarter.
The fact that legal sales increased so dramatically while actually consumption only raised slightly must mean that cannabis consumers are quickly transitioning to the legal market concluded the researchers.
"Given that wastewater represents a total population measure, these findings suggest that many established users switched from the illegal to the legal market," reads the study. "This is the strongest statement possible regarding displacement of the illegal market."
Washington isn't the only place turning to the toilet to chart peoples' cannabis consumption habits. Statistics Canada has run similar studies which they have used to figure out which Canadian cities consume the most cannabis.