The estimation of cannabis consumption through wastewater analysis

Cannabis is the most commonly used illicit drug worldwide. Its use is becoming less stigmatized as illustrated by the increasing public opinion towards legalization in many countries. Accurate and reliable data on cannabis consumption is, however, needed to assess the impact of new policies and plan prevention strategies carefully. To this aim, measuring drug residues in wastewater, which represent anonymous urine samples of entire populations, can provide valuable information on patterns and trends of drug use, complementing traditional data. This trans-disciplinary approach, known as wastewater-based epidemiology, has demonstrated its value and is well established for monitoring illicit drugs, such as cocaine and amphetamine-type stimulants. However, measuring the main human urinary metabolites of cannabis in wastewater has presented additional challenges and uncertainties related to the analytical measurements, stability and poorly understood excretion rates. Consequently, results often suggested an overestimation of consumption. This chapter aims to identify key aspects, which demand attention and demonstrate the current utility and potential of wastewater analysis for the estimation of cannabis consumption.