What data are available on the extent of illicit drug use and dependence globally? Results of four systematic reviews

Abstract

Background

We systematically reviewed availability and quality of data on the prevalence of use and dependence on meth/amphetamine, cannabis, cocaine and opioids.

Methods

Multiple search strategies: (a) peer-reviewed literature searches (1990–2008) using methods recommended by the Meta-analysis of Observational Studies in Epidemiology (MOOSE) group; (b) systematic searches of online databases; (c) Internet searches to find other published evidence of drug use; (d) repeated consultation and feedback from experts around the globe; (e) a viral email sent to lists of researchers in the illicit drug and HIV fields. Data were extracted and graded according to predefined variables reflecting quality of data source.

Results

Qualitative evidence of illicit drug use and dependence was found for most countries, which hold over 98% of the world's population aged 15–64 years. Countries where use was identified but prevalence estimates had not been made (evidence of drug supply, trafficking, reports of use, treatment data) were mainly from Asia, Africa, the Middle East, and Oceania. Estimates of the prevalence of use were located in 77 countries for meth/amphetamine, 95 for cannabis, 86 for cocaine and 89 for opioids. Dependence prevalence estimates existed in very few countries; 9 meth/amphetamine dependence estimates, 7 cannabis dependence estimates, 5 cocaine dependence estimates, and 25 opioid dependence estimates were located.

Conclusions

Data on the extent of meth/amphetamine, cannabis, cocaine and opioid use and dependence must be improved in quality and coverage. Dependence estimates are lacking even in high income countries that have required resources. Responses to illicit drug dependence require better estimates of its scale.

Introduction

The illicit use of meth/amphetamine, cannabis, cocaine, and opioids has been documented in many countries, but large gaps remain in our knowledge of the extent of the use of these drugs, and especially the extent of problem or dependent use (United Nations Office on Drugs and Crime, 2009a). The problematic use of illicit drugs is associated with considerable mortality and morbidity. Meth/amphetamine use, for example, has been associated with: HIV infection and transmission, and negative impacts on people living with HIV (Degenhardt et al., 2010); acute psychotic episodes following heavy or “binge” use (Batki and Harris, 2004, Segal and Kuczenski, 1997, Srisurapanont et al., 2003); violent or aggressive behaviour during acute intoxication (Boles and Miotto, 2003, McKetin et al., 2006, Wright and Klee, 2001); and increased overdose mortality (De Letter et al., 2006). Cannabis use before the age of 15 years increases a person's risk of becoming dependent (Hall and Degenhardt, 2007); heavy cannabis use in turn appears to increase the risk of: motor vehicle accidents, psychosis and mood disorders (Calabria et al., 2010, Degenhardt et al., 2001, Hall and Degenhardt, 2009). Cocaine dependence has also been associated with paranoia (Mooney et al., 2006, Satel et al., 1991), suicide (Marzuk et al., 1992, Roy, 2001), overdose mortality (Degenhardt et al., 2011a), HIV infection (Mathers et al., 2008, Ribeiro et al., 2006), and poor health outcomes (Cornish and O’Brien, 1996, Cregler, 1989, Falck et al., 2003). Opioid users may struggle with dependence over many years, and suffer from poor health, elevated mortality (Bargagli et al., 2006, Degenhardt et al., 2011b, Lejckova and Mravcik, 2007, Vlahov et al., 2008, Wall et al., 2000, World Health Organization, 2004, Zhang et al., 2005) particularly overdose (Degenhardt et al., 2006, Degenhardt et al., 2004), and HIV and HCV infection (World Health Organization, 2004). These drug-related problems are particularly common in people who use high doses of these drugs frequently, and who qualify for a diagnosis of dependence. Drug dependence can cause considerable harm to the individual, the community, and has important implications for public health and social policy (Greater London Alcohol and Drug Alliance, 2004, United, 2008a, United, 2009b).

It is important to carefully review and describe the nature of data on the extent of drug use and dependence in each country and globally: if not, it is difficult to accurately inform the nature and scale of public health responses. It is also important to highlight what is – and what is not – known about the extent of drug use and dependence. This is important, because illicit drug use makes a substantial contribution to the global burden of disease: in 2000, it was estimated that illicit drug use (broadly defined as “problem” or injecting use of opioids, cocaine, or amphetamines) explained 0.8% of the global burden of disease (Degenhardt et al., 2004); it is likely to be an underestimate of total burden today because it excludes cannabis, some important consequences of injecting drug use (e.g. hepatitis B and C), and there have been significant shifts in drug markets over the past decade (Reuter and Trautmann, 2009, United, 2009b). Ten years on, there was a need to review our knowledge of the extent of illicit drug use to update and revise estimates of the global burden of disease attributable to illicit drug use (Degenhardt et al., 2009d).

The World Drug Report (WDR), which is produced annually by the United Nations Office on Drugs and Crime (UNODC), is the only global review of drug use, seizures, trafficking and cultivation of illicit drugs. The WDR relies on each member state completing an Annual Reports Questionnaire (ARQ), and depends upon a wide range of data of varying quality. In many cases, the evidence on which these estimates are based is not reported by Member States; UNODC is further limited in its capacity (due to resource and time restrictions) to systematically review the peer reviewed and grey literature. There are large data gaps within the WDR, particularly in Africa, Asia and Oceania.

To date, there has never been a systematic multistage review of the global coverage of illicit drug dependence estimates, nor any assessment of qualitative evidence of illicit drug use when there are no prevalence estimates. This paper aims to fill these gaps by presenting the findings of a systematic review of the global coverage of illicit drug use and dependence estimates. The aims of this paper are to:

• describe the availability of country-level data on the prevalence of meth/amphetamine, cannabis, cocaine and opioid use and dependence; and

• identify research priorities for improving the quality and coverage of such estimates.