Estimating Illicit Stimulant Drug Consumption in Luxembourg Using Wastewater-Based Epidemiology.

Wastewater-based epidemiology (WBE) is a reliable complement to traditional drug-use monitoring approaches such as surveys and law-enforcement statistics, yet evidence from small countries with heterogeneous population settings remains limited. This study applied WBE to estimate community-level consumption and geographical variation of four illicit stimulant drugs (amphetamine, cocaine as benzoylecgonine, methamphetamine and 3,4-methylenedioxymethamphetamine [MDMA]) across the Grand Duchy of Luxembourg, representing urban, periurban and rural contexts. Weekly time-proportional influent wastewater samples were collected during 2024 from five wastewater treatment plants. Target drugs and metabolites were extracted using solid-phase extraction and quantified by liquid chromatography coupled to triple quadrupole mass spectrometry. Consumption estimates were normalised to population size using established correction factors and drug purity estimates from analysis carried out on seizures in 2024. A total of 255 samples were analysed with 100% detection frequency for cocaine, 99.6% for MDMA, 92.5% for amphetamine and 79.2% for methamphetamine. Estimated consumption levels were highest in the treatment plant serving Luxembourg City and lowest in the most rural setting. Significant increases were observed for cocaine and MDMA during weekends. Drug consumption showed linear correlations with population size across all substances. Annual consumption estimates identified cocaine as the most consumed illicit stimulant in Luxembourg. Wastewater-based epidemiology allows a nonbiased estimation of stimulant drug consumption in Luxembourg, revealing distinct spatial patterns with higher consumption in urban than in rural areas, as well as pronounced increases during weekends. These findings demonstrate the utility of this approach in complementing traditional drug surveillance systems and supporting evidence-informed public health responses.