Trends in illicit and licit substance use across Spain – A comprehensive three-year wastewater-based epidemiology study.

The Spanish Network ESAR-Net was created in 2017 to implement wastewater-based epidemiology (WBE) at national scale and funded by “Plan Nacional Sobre Drogas (PNSD)” in the period 2021-2023 and performed a spring 1-week sampling campaign per year covering ca. 30 wastewater treatment plants (WWTPs) and an autumn 1-week campaign per year, focused into ca. 10 WWTPs. The WWTPs were selected to cover 10 (of the 17) Spanish regions, as well as different populations (from ca. 5,000 to over 1,000,000 inhabitants) and socioeconomic characteristics. The samples collected are analysed in the different laboratories of the network for illicit drugs, alcohol and tobacco use, including a screening of some selected new-psychoactive substances (NPS). The results of our study confirm that cannabis and cocaine are the most popular illicit drugs in Spain. Similarly, ecstasy prevalence is fairly uniform across the country. Also, results are, in general terms, comparable to those obtained in a pilot study in 18 WWTPs in 2018 supporting that the COVID-19 crisis (with still restrictions on place in 2021) has not impacted much drugs use, nor alcohol and nicotine intake. On the other hand, amphetamine and methamphetamine use show clear regional patterns, as compared to other drugs. Thus, amphetamine use is ca. 10-fold higher in the 3 locations from the Basque Country as compared to the rest of Spain, with WBE-estimated use being similar to that of cocaine (ca. 1-2 g / day / 1000 inhabitants). As regards to methamphetamine, its use in Spain is very low (many samples are below the quantification limit), in general terms. However, a niche of users exists in the two larger cities and particularly in the area of Barcelona (ca. 100-200 mg / day / 1000 inhabitants), followed by some areas of Madrid (ca. 10-50 mg / day / 1000 inhabitants). Interestingly, the enantiomeric analysis of the samples showed that in 2021 some of the methamphetamine detectable, particularly in the area of Madrid, was racemic or exhibited a mixture of the two enantiomers. This contrasts with traditional findings in Spain and most of Europe and may indicate that new supply routes for this substance would have partly entered the illicit market. As regards the NPS, their presence in the samples was rather marginal, with the exception of ketamine. This substance is now present in most locations reaching in some cases loads similar to or higher than the metabolite of cocaine. A potential explanation for that could be the popularization of the so called “pink cocaine”, which typically consists of ketamine mixed with a stimulant at lower doses. Furthermore, a study at different special events (festivities, parades, music festivals, etc) was conducted during 2023, where the particular use of stimulants and NPS could be measured.

This work is funded by the Spanish PNSD (2020I009), MCIN/AEI/10.13039/501100011033 (RED2022-134363-T) & Instituto de Salud Carlos III- NextGenerationEU/PRTR funds (RD21/0009/0012).