Drugs policy over the last two decades in the UK, and other countries, such as the US and Australia, has been very strongly influenced by the assumed link between drugs and crime (HM Government, 2010; Home Office, 2011, 2016) and the idea that tackling drug use will affect crime. Existing evidence suggests a strong link between illicit drug use and involvement in crime (Bennett, Holloway, & Farrington, 2008), especially incomegenerating, acquisitive crime (Bukten et al., 2011b). The association has been observed primarily among arrestees (Pierce et al.,2015b), prisoners (Johnson, 2006) and people entering drug treatment (Darke et al., 2009). However, these groups may not be representative of the wider drug-using population as offending rates can be atypical in the period immediately prior to arrest, imprisonment or treatment (McGlothlin, Anglin, & Wilson, 1978); and drug-using offenders may be more likely than non-using offenders to be apprehended (Bond & Sheridan, 2007).

The drug-crime link appears particularly compelling among individuals with frequent and problematic use of opiates, such as heroin (Kaye, Darke, & Finlay-Jones, 1998), and/or crack cocaine (Bennett et al., 2008; Comiskey, Stapleton, & Kelly, 2012). Evidence synthesis concludes that the odds of offending are six times greater for crack users than non-crack users and three times greater for heroin users than non-heroin users (Bennett et al., 2008). Opiate/ crack users comprise 81% of those in receipt of structured drugtreatment services in England and are the group predominantly targeted by policy initiatives to divert drug-using offenders into treatment (Home Office, 2011; PHE, 2014). For these reasons, our review focuses on opiate/crack users.

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