Burgard DA, et al. - Researchers examined how newly legalized retail cannabis sales have influenced its use via a wastewater-based analysis. In addition, they assessed if the size of the legal market place, which began August 1, 2014 in the study area, could be projected using this approach. They collected and analyzed raw wastewater samples over the 3-year period from 2014 to 2016. From the two wastewater treatment plants that serviced a municipality of 200,000 people in the state of Washington, the samples were obtained. Via liquid chromatography coupled to mass spectrometry, they determined metabolite of the active ingredient in cannabis, 11-nor-9-Carboxy-Δ9-tetrahydrocannabinol in this quantitative analysis of 24-hour composite influent samples. Findings determined a significant increase in cannabis consumption in Washington following legalization, and that a large portion of the illicit market has been displaced by the legal sales. This data could not be used to assess the proportion of the total cannabis market supplied by state-regulated cannabis.