Background and Aims Drug checking services provide people who use drugs with chemical analysis results of their drug samples while simultaneously monitoring the unregulated drug market. We sought to identify and synthesize literature on the following domains: (a) the influence of drug checking services on the behaviour of people who use drugs; (b) monitoring of drug markets by drug checking services; and (c) outcomes related to models of drug checking services. Methods Systematic review. A systematic literature search was conducted in MEDLINE, Embase, Cochrane Central Register of Controlled Trials, Cochrane Database of Systematic Reviews, PsycINFO, Scopus, Web of Science and Dissertations and Theses Global. Eligible studies were peer‐reviewed articles and conference abstracts or grey literature, published in any language since 1990 and including original data on the domains. We assessed risk of bias for quantitative peer‐reviewed articles reporting on behaviour or models of drug checking services using National Institutes of Health tools. Results We screened 2463 titles and abstracts and 156 full texts, with 90 studies meeting inclusion criteria. Most (n = 65, 72.2%) were from Europe and used cross‐sectional designs (n = 79, 87.7%). Monitoring of drug markets by drug checking services (n = 63, 70%) was the most reported domain, followed by the influence of drug checking services on behaviour (n = 31, 34.4%), including intent to use, actual use and disposal of the drug, and outcomes related to models of drug checking services (n = 17, 18.9%). The most common outcome measures were detection of unexpected substances (n = 50, 55.6%), expected substances (n = 44, 48.9%), new psychoactive substances (n = 40, 44.4%) and drugs of concern (n = 32, 36.5%) by drug checking services. Conclusions Drug checking services appear to influence behavioural intentions and the behaviour of people who use drugs, particularly when results from drug checking services are unexpected or drugs of concern. Monitoring of drug markets by drug checking services is well established in Europe, and increasingly in North America. Concerns about drug contents and negative health consequences facilitate the use of drug checking services; lack of concern; trust in drug sellers; lack of accessibility of drug checking services; and legal and privacy concerns are barriers to use.

THIS PREPRINT HAS BEEN UPDATED AND FORMALLY PUBLISHED IN _ADDICTION_ [https://onlinelibrary.wiley.com/doi/10.1111/add.15734] (HTTPS://DOI.ORG/10.1111/ADD.15734 [https://doi.org/10.1111/add.15734]). A ONE-PAGE FACT SHEET [https://cdpe.org/publication/drug-checking-services-for-people-who-use-drugs-a-systematic-review/] IS ALSO AVAILABLE. BACKGROUND AND AIMS: Drug checking services (DCS) provide people who use drugs (PWUD) with chemical analysis results of their drug samples, while simultaneously monitoring the unregulated drug market. We sought to identify and synthesize literature on the following domains: (a) influence of DCS on behaviour of PWUD; (b) monitoring of drug markets by DCS; and (c) outcomes related to models of DCS. METHODS: This review followed PRISMA guidelines and was pre-registered in PROSPERO (CRD42018105366). A systematic literature search was conducted in MEDLINE, Embase, Cochrane Central Register of Controlled Trials, Cochrane Database of Systematic Reviews, PsycINFO, Scopus, Web of Science, and Dissertations & Theses Global. Eligible studies were peer-reviewed articles and conference abstracts, or grey literature, published in any language since 1990 and including original data on the domains. We assessed risk of bias for quantitative peer-reviewed articles reporting on behaviour or models of DCS using National Institutes of Health tools. RESULTS: We screened 2,463 titles and abstracts and 156 full-texts, with 90 studies meeting inclusion criteria. Most (n=65, 72.2%) were from Europe and used cross-sectional designs (n=79, 87.7%). Monitoring of drug markets by DCS (n=63, 70%) was most commonly reported, followed by influence of DCS on behaviour (n=31, 34.4%) and outcomes related to models of DCS (n=17, 18.9%). The most common outcome measures were detection of unexpected substances (n=50, 55.6%), expected substances (n=44, 48.9%), new psychoactive substances_ _(n=40, 44.4%), and drugs of concern (n=32, 36.5%) by DCS. CONCLUSIONS: Monitoring of drug markets by DCS is well established in Europe and increasingly in North America. There is an emerging evidence base demonstrating the capacity of DCS to influence behavioural intention, and a smaller subset of findings on its impact on the enacted behaviour of PWUD. Further research is needed on enacted behaviours and corresponding health outcomes including overdose, particularly among people who inject drugs or use opioids.

Issues. Non-medical prescription opioid use (NMPOU) contributes substantially to the global burden of morbidity. However, no systematic assessment of the scientific literature on the associations between NMPOU and health outcomes has yet been undertaken. Approach. We undertook a systematic review evaluating health outcomes related to NMPOU based on ICD-10 clinical domains. We searched 13 electronic databases for original research articles until 1 July 2021. We employed an adaptation of the Oxford Centre for Evidence-Based Medicine 'Levels of Evidence' scale to assess study quality. Key Findings. Overall, 182 studies were included. The evidence base was largest on the association between NMPOU and mental and behavioural disorders; 71% (129) studies reported on these outcomes. Less evidence exists on the association of NMPOU with infectious disease outcomes (26; 14%), and on external causes of morbidity and mortality, with 13 (7%) studies assessing its association with intentional self-harm and 1 study assessing its association with assault (<1%). Implications. A large body of evidence has identified associations between NMPOU and opioid use disorder as well as on fatal and non-fatal overdose. We found equivocal evidence on the association between NMPOU and the acquisition of HIV, hepatitis C and other infectious diseases. We identified weak evidence regarding the potential association between NMPOU and intentional self-harm, suicidal ideation and assault. Discussion and Conclusions. Findings may inform the prevention of harms associated with NMPOU, although higher-quality research is needed to characterise the association between NMPOU and the full spectrum of physical and mental health disorders.

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