"A public health intervention operating for more than 50 years, drug checking services (DCS) allow the public to submit drug samples from unregulated drug markets (i.e. illegal and legal drugs sold through criminal channels) for chemical analysis. DCS emerged across the United States in the late 1960s and early 1970s during the rise of a psychedelic counterculture that championed the use of psychoactive substances to expand consciousness [1, 2]. DCS were later expanded in European settings throughout the 1990s, beginning in the Netherlands, primarily in response to the popularity of dance events and associated use of 3,4-methylenedioxymethamphetamine (MDMA) and other drugs [3, 4]. More recently, DCS have been implemented in Australasia, the Americas and the United Kingdom, often with an emphasis on preventing harms from new psychoactive substances (NPS), including synthetic opioids. A global review of DCS conducted in 2017 identified 31 services operating across 20 countries . Notably, the contamination of unregulated drug markets with fentanyl and the resulting opioid overdose crisis has motivated the recent expansion of DCS in Canada  and the United States .
"DCS provide people who use drugs (PWUD) with information on the chemical composition of their drug samples to facilitate more informed decision-making . While some analysis methods can be operated by PWUD, DCS typically offer tailored harm reduction advice with the provision of analysis results to PWUD . By aggregating data on the composition of drug samples, DCS provide insight into trends in the unregulated drug supply and inform policymaking and harm reduction activities at the population level . DCS can inform public health alerts  when drugs of concern are detected, thus offering potential benefits to the broader community of PWUD and service providers . DCS differ globally in terms of their legality and degree of government support, as well as where and how samples are collected and analysed. Models include mobile services at events, fixed services where samples can be dropped off or mailed and the distribution of analysis methods for personal use, all of which employ a variety of technologies with differing benefits and drawbacks [8, 13, 14]."
Maghsoudi N, Tanguay J, Scarfone K, Rammohan I, Ziegler C, Werb D, et al. Drug checking services for people who use drugs: a systematic review. Addiction. 2021;1–13. doi.org/10.1111/add.15734