The COVID-19 outbreak has forced countries to introduce severe restrictive measures to contain its spread . In particular, physical distancing and restriction of movement have important consequences on human behaviour and potentially also on illicit drug use and supply . These changes can be associated with additional risks for users due to reduced supplies, limited prevention and harm reduction activities . Furthermore, there have been limitations in the amount of data about drug use which can be collected due to restrictions . To goal of this study was to obtain information about potential changes in illicit drug use impacted by COVID-19 restrictions . Wastewater samples were collected in seven cities in the Netherlands, Belgium, Spain and Italy at the beginning of lockdowns (March-May 2020). Using previously established and validated methods, levels of amphetamine (AMP), methamphetamine (METH), MDMA, benzoylecgonine (BE, the main metabolite of cocaine) and 11-nor-9-carboxy-Δ9-tetrahydrocannabinol (THC-COOH, main metabolite of tetrahydrocannabinol (THC) ) were measured and compared with findings from previous years . Important differences in levels of consumed drugs were observed across the considered countries . Whilst for some substances and locations, marked decreases in consumption could be observed (e.g. , 50% decrease in MDMA levels compared to previous years). In some cases, similar or even higher levels compared to previous years could be found . Changes in weekly patterns were also observed, however these were not clearly defined for all locations and/or substances . Findings confirm that the current situation is highly heterogeneous and that it remains very difficult to explain and/or predict the effect that the present pandemic has on illicit drug use and availability . However, given the current difficulty in obtaining data due to restrictions, wastewater analysis can provide relevant information about the situation at the local level, which would be hard to obtain otherwise.