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No single measure is able to provide a complete picture of population- or community-level drug abuse and its current trends. Therefore, a multi-indicator approach is needed. The aim of this study was to combine wastewater-based epidemiology (WBE) with data from other national indicators, namely driving under the influence of drugs (DUID) statistics, drug seizures, and drug use surveys. Furthermore, drug market size estimates and a comparison of confiscated drugs to drugs actually consumed by users were performed using the WBE approach. Samples for wastewater analysis were collected during one-week sampling periods in 2012, 2014 and 2015, with a maximum of 14 cities participating. The samples were analysed with a validated ultra-high-performance liquid chromatography-mass spectrometric (UHPLC-MS/MS) methodology for various common drugs of abuse. The results were then compared with data from other national indicators available. Joint interpretation of the data shows that the use of amphetamine and MDMA has increased in Finland from 2012 to 2014. A similar trend was also observed for cocaine, although its use remains at a very low level compared to many other European countries. Heroin was practically absent from the Finnish drug market during the study period. The retail market for the most common stimulant drugs were estimated to have been worth EUR 70 million for amphetamine and around EUR 10 million for both methamphetamine and cocaine, in 2014 in Finland.

Estimations of drug use at the national level are generally based on various sources of information, such as drug seizures, socio-scientific studies, toxicological data and hospital records. Nevertheless, all of these approaches have limitations that cannot be overcome, even if conclusions are drawn from combined data retrieved from different sources. Drug epidemiology through wastewater analysis has the potential to provide unique perspectives, internationally comparable data, and up-to-date information on the use of both traditional illicit drugs and new psychoactive substances (NPSs). In Finland, no large-scale studies on regional illicit drug consumption, based on a wastewater approach, have been reported. In this study, 24-h influent composite samples were collected during two 1-week study periods from ten different wastewater treatment plants in May and November–December 2012. The cities included in the study represent the geographical areas throughout Finland and cover 40% of the Finnish population. The samples were analyzed with an in-house validated, ultra high-performance liquid–chromatography mass spectrometric (UHPLC–MS/MS) method for various common illicit drugs and some NPS type stimulant drugs. The results were also compared with available statistics, information on drug seizures and laboratory-confirmed toxicological data, as well as other studies available based on wastewater analysis. The data show that illicit stimulant drug use is more common in the larger cities of Southern Finland. Amphetamine was the most commonly used drug in all 10 cities during both collection periods (excluding the collection period in May in Lappeenranta). Cocaine consumption remains very low in Finland in comparison to other European countries; it was concentrated in the biggest cities in Southern Finland. This study shows interesting temporal and spatial differences in drug use in Finland, as well as the possibilities of using wastewater analytics to reveal local hotspots of NPS consumption.