The CDPE conducts systematic reviews to generate the best available evidence to guide drug policies. Our systematic reviews analyze the effectiveness of policies and interventions that aim to prevent, treat, or reduce harms related to problematic substance use.

By developing a strong body of evidence to identify the most impactful strategies as well as potentially wasteful or harmful interventions, these studies can contribute to advancing evidence-based drug policies that promote health and human rights.

To request a copy of any publication that is not open access, please email info@cdpe.org. Current and past systematic reviews include:

Drug checking services for people who use drugs: A systematic review
Maghsoudi N, Tanguay J, Scarfone K, Rammohan I, Ziegler C, Werb D, Scheim AI

Abstract | Full Article | One-Page Fact Sheet | Podcast

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.

Prevalence and correlates of providing and receiving assistance with the transition to injection drug use
Gicquelais RE, Werb D, Marks C, Ziegler C, Mehta SH, Genberg BL, Scheim AI

Abstract | Full Article

Background: Preventing the transition to injection drug use is an important public health goal, as people who inject drugs (PWID) are at high risk for overdose and acquisition of infectious disease. Initiation into drug injection is primarily a social process, often involving PWID assistance. A better understanding of the epidemiology of this phenomenon would inform interventions to prevent injection initiation and to enhance safety when assistance is provided.

Objectives:  We conducted a systematic review of the literature to 1) characterize the prevalence of receiving (among injection-naive persons) and providing (among PWID) help or guidance with the first drug injection and 2) identify correlates associated with these behaviors. Correlates were organized as substance use behaviors, health outcomes (e.g., human immunodeficiency virus infection), or factors describing an individual’s social, economic, policy, or physical environment, defined by means of Rhodes’ risk environments framework.

Results: After screening of 1,164 abstracts, 57 studies were included. The prevalence of receiving assistance with injection initiation (help or guidance at the first injection) ranged 74% to 100% (n = 13 estimates). The prevalence of ever providing assistance with injection initiation varied widely (range, 13%–69%; n = 13 estimates). Injecting norms, sex/gender, and other correlates classified within Rhodes’ social risk environment were commonly associated with providing and receiving assistance.

Conclusions: Nearly all PWID receive guidance about injecting for the first time, whereas fewer PWID report providing assistance. Substantial clinical and statistical heterogeneity between studies precluded meta-analysis, and thus local-level estimates may be necessary to guide the implementation of future psychosocial and sociostructural interventions. Further, estimates of providing assistance may be downwardly biased because of social desirability factors.

Impact evaluations of drug decriminalisation and legal regulation on drug use, health and social harms: A systematic review
Scheim AI, Maghsoudi N, Marshall Z, Churchill S, Ziegler C, Werb D

Abstract | Full Article

Objectives: To review the metrics and findings of studies evaluating effects of drug decriminalisation or legal regulation on drug availability, use or related health and social harms globally.

Design: Systematic review with narrative synthesis.

Data sources: We searched MEDLINE, Embase, PsycINFO, Web of Science and six additional databases for publications from 1 January 1970 through 4 October 2018.

Inclusion criteria: Peer-reviewed articles or published abstracts in any language with quantitative data on drug availability, use or related health and social harms collected before and after implementation of de jure drug decriminalisation or legal regulation.

Data extraction and synthesis: Two independent reviewers screened titles, abstracts and articles for inclusion. Extraction and quality appraisal (modified Downs and Black checklist) were performed by one reviewer and checked by a second, with discrepancies resolved by a third. We coded study-level outcome measures into metric groupings and categorised the estimated direction of association between the legal change and outcomes of interest.

Results: We screened 4860 titles and 221 full-texts and included 114 articles. Most (n=104, 91.2%) were from the USA, evaluated cannabis reform (n=109, 95.6%) and focused on legal regulation (n=96, 84.2%). 224 study outcome measures were categorised into 32 metrics, most commonly prevalence (39.5% of studies), frequency (14.0%) or perceived harmfulness (10.5%) of use of the decriminalised or regulated drug; or use of tobacco, alcohol or other drugs (12.3%). Across all substance use metrics, legal reform was most often not associated with changes in use.

Conclusions: Studies evaluating drug decriminalisation and legal regulation are concentrated in the USA and on cannabis legalisation. Despite the range of outcomes potentially impacted by drug law reform, extant research is narrowly focused, with a particular emphasis on the prevalence of use. Metrics in drug law reform evaluations require improved alignment with relevant health and social outcomes.

The experience of initiating injection drug use and its social context: A qualitative systematic review and thematic synthesis
Guise A, Horyniak D, Melo J, McNeil R, Werb D

Abstract | Full Article

Background and Aim: Understanding the experience of initiating injection drug use and its social contexts is crucial to inform efforts to prevent transitions into this mode of drug consumption and support harm reduction. We reviewed and synthesized existing qualitative scientific literature systematically to identify the socio-structural contexts for, and experiences of, the initiation of injection drug use.

Methods: We searched six databases (Medline, Embase, PsychINFO, CINAHL, IBSS and SSCI) systematically, along with a manual search, including key journals and subject experts. Peer-reviewed studies were included if they qualitatively explored experiences of or socio-structural contexts for injection drug use initiation. A thematic synthesis approach was used to identify descriptive and analytical themes throughout studies.

Results: From 1731 initial results, 41 studies reporting data from 1996 participants were included. We developed eight descriptive themes and two analytical (higher-order) themes. The first analytical theme focused on injecting initiation resulting from a social process enabled and constrained by socio-structural factors: social networks and individual interactions, socialization into drug-using identities and choices enabled and constrained by social context all combine to produce processes of injection initiation. The second analytical theme addressed pathways that explore varying meanings attached to injection initiation and how they link to social context: seeking pleasure, responses to increasing tolerance to drugs, securing belonging and identity and coping with pain and trauma.

Conclusions: Qualitative research shows that injection drug use initiation has varying and distinct meanings for individuals involved and is a dynamic process shaped by social and structural factors. Interventions should therefore respond to the socio-structural influences on injecting drug use initiation by seeking to modify the contexts for initiation, rather than solely prioritizing the reduction of individual harms through behavior change.

Topiramate for cocaine dependence: A systematic review and meta‐analysis of randomized controlled trials
Singh M, Keer D, Klimas J, Wood E, Werb D

Abstract | Full Article

Aims: To assess the efficacy of topiramate in treating cocaine use disorder (i.e. retention, efficacy, safety and craving reduction) through a systematic review and meta-analysis.

Methods: We searched six scientific databases from inception to 23 December 2014 with no date limits. Data were reviewed, extracted and analysed systematically. Studies were included if they were peer-reviewed randomized control trials with participants meeting diagnostic criteria for cocaine dependence or cocaine use disorder, with the treatment arm involving topiramate with or without psychosocial intervention, and the control arm involving no intervention or psychosocial intervention with or without placebo. A random-effects meta-analytical model was computed.

Results: Five studies met inclusion criteria (n = 518). Topiramate was compared with placebo (four studies) and no medication (one study). In a meta-analysis, we observed no significant differences between topiramate and placebo in improving treatment retention risk ratio (RR) = 0.85; 95% confidence interval (CI) = 0.60-1.22, P = 0.38. However, compared with a placebo, use of topiramate was associated with increased continuous abstinence in two of five studies (RR = 2.43; 95% CI = 1.31-4.53, P = 0.005). No differences were observed in frequency of adverse effects reported between topiramate and placebo (RR = 1.06; 95% CI = 0.91-1.23, P = 0.48). Topiramate was associated significantly (P < 0.05) with a reduction in craving in only one of five studies.

Conclusions: Evidence does not currently support the use of topiramate to improve treatment retention for cocaine use disorder, although it may extend cocaine abstinence with a similar risk of adverse events compared with placebo.

The effectiveness of compulsory drug treatment: A systematic review
Werb D, Kamarulzaman A, Meacham MC, Rafful C, Fischer B, Strathdee SA, Wood E

Abstract | Full Article | One-Page Fact Sheet

Background: Despite widespread implementation of compulsory treatment modalities for drug dependence, there has been no systematic evaluation of the scientific evidence on the effectiveness of compulsory drug treatment.

Methods: We conducted a systematic review of studies assessing the outcomes of compulsory treatment. We conducted a search in duplicate of all relevant peer-reviewed scientific literature evaluating compulsory treatment modalities. The following academic databases were searched: PubMed, PAIS International, Proquest, PsycINFO, Web of Science, Soc Abstracts, JSTOR, EBSCO/Academic Search Complete, REDALYC, SciELO Brazil. We also searched the Internet, and article reference lists, from database inception to July 15th, 2015. Eligibility criteria are as follows: peer-reviewed scientific studies presenting original data. Primary outcome of interest was post-treatment drug use. Secondary outcome of interest was post-treatment criminal recidivism.

Results: Of an initial 430 potential studies identified, nine quantitative studies met the inclusion criteria. Studies evaluated compulsory treatment options including drug detention facilities, short (i.e., 21-day) and long-term (i.e., 6 months) inpatient treatment, community-based treatment, group-based outpatient treatment, and prison-based treatment. Three studies (33%) reported no significant impacts of compulsory treatment compared with control interventions. Two studies (22%) found equivocal results but did not compare against a control condition. Two studies (22%) observed negative impacts of compulsory treatment on criminal recidivism. Two studies (22%) observed positive impacts of compulsory inpatient treatment on criminal recidivism and drug use.

Conclusions: There is limited scientific literature evaluating compulsory drug treatment. Evidence does not, on the whole, suggest improved outcomes related to compulsory treatment approaches, with some studies suggesting potential harms. Given the potential for human rights abuses within compulsory treatment settings, non-compulsory treatment modalities should be prioritized by policymakers seeking to reduce drug-related harms.

Interventions to prevent the initiation of injection drug use: A systematic review
Werb D, Buxton J, Shoveller J, Richardson C, Rowell G, Wood E

Abstract | Full Article

Background: Injection drug use has been identified as a key source of morbidity and mortality, primarily from overdose and the transmission of blood-borne diseases such as HIV. Experts have therefore called for the prioritization of resources toward the prevention of injection drug use. However, these strategies have not been systematically assessed.

Methods: PRISMA guidelines were used to systematically review and extract findings from the peer-reviewed literature evaluating the effectiveness of interventions to prevent injecting initiation. We searched 10 English language electronic databases (PubMed, PsycINFO, EMBASE, Cochrane CENTRAL, CINAHL, Web of Science, TOXNET, AIDSLINE, AMED and ERIC), the Internet (Google, Google Scholar), and article reference lists, from database inception to June 1st, 2012.

Results: Overall, out of 384 studies identified in the initial search, eight met the inclusion criteria. Studies evaluated four different types of interventions: social marketing, peer-based behavior modification, treatment, and drug law enforcement. Four studies observed a significant effect of the intervention on reducing rates of injecting initiation. Peer-based behavior modification and addiction treatment interventions were found to be most effective. Two of three studies assessing the impact of drug law enforcement on patterns of injecting initiation found no impact on injecting initiation, while one study reported inconclusive results.

Conclusion: There exists a limited scientific literature on strategies to prevent injecting initiation. Resources should be allocated toward increased research and development of effective interventions to prevent this phenomenon.

The effectiveness of anti-illicit-drug public-service announcements: A systematic review and meta-analysis
Werb D, Mills EJ, DeBeck K, Kerr T, Montaner JSG, Wood E

Abstract | Full Article

Background: Anti-illicit-drug public-service announcements (PSAs) have become a cornerstone of drug policy in the USA. However, studies of the effectiveness of these interventions have not been subjected to a systematic evaluation.

Methods: The authors searched 10 electronic databases along with major conference abstract databases (from inception until 15 February 2010) for all articles and abstracts that evaluated the effectiveness of anti-illicit-drug PSAs. The authors evaluated all studies that assessed intention to use illicit drugs and/or levels of illicit-drug use after exposure to PSAs, and conducted meta-analyses of these studies.

Results: The authors identified seven randomised trials (n=5428) and four observational trials (n=17 404). Only one randomised trial showed a statistically significant benefit of PSAs on intention to use illicit drugs, and two found evidence that PSAs significantly increased intention to use drugs. A meta-analysis of eligible randomised trials demonstrated no significant effect. Observational studies showed evidence of both harmful and beneficial effects.

Conclusion: Existing evidence suggests that the dissemination of anti-illicit-drug PSAs may have a limited impact on the intention to use illicit drugs or the patterns of illicit-drug use among target populations.

Effect of drug law enforcement on drug market violence: A systematic review
Werb D, Rowell G, Guyatt G, Kerr T, Montaner J, Wood E

Abstract | Full Article

Violence is amongst the primary concerns of communities around the world and research has demonstrated links between violence and the illicit drug trade, particularly in urban settings. Given the growing emphasis on evidence-based policy-making, and the ongoing severe drug market violence in Mexico and other settings, we conducted a systematic review to examine the impacts of drug law enforcement on drug market violence. We conducted a systematic review using Preferred Reporting Items for Systematic Reviews and Meta Analyses (PRISMA) guidelines. Specifically, we undertook a search of English language electronic databases (Academic Search Complete, PubMed, PsycINFO, EMBASE, Web of Science, Sociological Abstracts, Social Service Abstracts, PAIS International and Lexis-Nexis), the Internet (Google, Google Scholar), and article reference lists, from database inception to January 24, 2011. Overall, 15 studies were identified that evaluated the impact of drug law enforcement on drug market violence, including 11 (73%) longitudinal analyses using linear regression, 2 (13%) mathematical drug market models, and 2 (13%) qualitative studies. Fourteen (93%) studies reported an adverse impact of drug law enforcement on levels of violence. Ten of the 11 (91%) studies employing longitudinal qualitative analyses found a significant association between drug law enforcement and drug market violence. Our findings suggest that increasing drug law enforcement is unlikely to reduce drug market violence. Instead, the existing evidence base suggests that gun violence and high homicide rates may be an inevitable consequence of drug prohibition and that disrupting drug markets can paradoxically increase violence. In this context, and since drug prohibition has not meaningfully reduced drug supply, alternative regulatory models will be required if drug supply and drug market violence are to be meaningfully reduced.

Health outcomes associated with methamphetamine use among young people: A systematic review
Marshall BD, Werb D

Abstract | Full Article

Objectives: Methamphetamine (MA) use among young people is of significant social, economic and public health concern to affected communities and policy makers. While responses have focused upon various perceived severe harms of MA use, effective public health interventions require a strong scientific evidence base.

Methods: We conducted a systematic review to identify scientific studies investigating health outcomes associated with MA use among young people aged 10-24 years. The International Classification of Diseases (ICD-10) was used to categorize outcomes and determine the level of evidence for each series of harms.

Results: We identified 47 eligible studies for review. Consistent associations were observed between MA use and several mental health outcomes, including depression, suicidal ideation and psychosis. Suicide and overdose appear to be significant sources of morbidity and mortality among young MA users. Evidence for a strong association between MA use and increased risk of human immunodeficiency virus (HIV) and other sexually transmitted infections is equivocal. Finally, we identified only weak evidence of an association between MA use and dental diseases among young people.

Conclusions: Available evidence indicates a consistent relationship between MA use and mental health outcomes (e.g. depression, psychosis) and an increased risk of mortality due to suicide and overdose. We found insufficient evidence of an association between MA use and other previously cited harms, including infectious diseases and dental outcomes. As such, future research of higher methodological quality is required to further investigate possible associations. Current interventions should focus attention upon MA-related health outcomes for which sound scientific evidence is available.

Financial Supporters 

Canadian Institutes of Health Research | Canadian Research Initiative in Substance Misuse | Government of Ontario: Ministry of Research, Innovation and Science | MAC AIDS Fund | Open Society Foundations

Project Contact

Dr. Ayden Scheim