Do police arrestees substitute legal highs for other drugs? (2016)

Background: Some commentators have suggested legal highs (LH) might reduce existing illegal drug use and contribute to lower drug-related harm. However, no studies have specifically investigated substitution between LH and other drugs.
Aims: To explore the extent to which police detainees substitute LH for illegal drugs. Method A total of 848 detainees at four central police stations were interviewed about their drug and LH use. Detainees were asked what impact their LH use had on their other drug use (i.e., 'no change', 'more', 'less' or 'stopped'). The detainees were placed into four groups: (i) no LH use; (ii) LH use and 'no change' in drug use; (iii) LH use and 'more' drug use; (iv) LH use and 'less' or 'stopped' drug use. Demographics and levels of drug use in the past month were compared between groups.
Results: Ninety-six percent of the LH using detainees had used synthetic cannabinoids (SC), and, of those who reported substituting a drug, 94% had substituted (natural) cannabis. Overall, 54% of the detainee sample had not used SC, 34% had used SC but not changed their cannabis use, 9% had used SC and used 'less' or 'stopped' cannabis use, and 3% had used SC and used 'more' cannabis. The SC users were more likely to have recently been in drug treatment. All those who used SC had higher cannabis consumption regardless of substitution behaviour. The SC users who used 'more' cannabis also used more methamphetamine and ecstasy.
Conclusion: Twenty percent of those who used SC and cannabis reported reducing or stopping their cannabis use while 6% increased their cannabis use, suggesting a modest overall reduction in cannabis use. Further research is required to quantify the magnitude of substitution changes, the impact on drug-related harm, and extent to which substitution occurs for other LH and other populations.