Co-using drugs-what do we need to know?

Abstract

Increasing co-use of cannabis and tobacco constitutes not only a warning about potentially increased drug use harms, but also directs attention to social and economic changes leading to a wider range of patterns of polydrug use. There is a need for research on these changes and many less common patterns of drug use and their consequences. The co-use of substances (often involving combinations of licit and illicit drugs) is emerging as a major health concern linked to overdosing and other adverse health outcomes [1]. It is in this context that the paper by Hindoch and McClure [2] argues that one pattern of substance use involving the co-use of cannabis and tobacco raises particular concerns that need to be addressed. Hindocha and McClure's [2] argument is largely in three parts. First, the concurrent administration of more than one substance (co-use), in this instance tobacco and cannabis, may lead to specific harms. Second, that there have been substantial recent changes with tobacco use declining whereas cannabis use has been increasing. The legalisation of cannabis in many jurisdictions and the move to competitive commercial cultivation of cannabis products possibly involving a greater concentration of active ingredients are contributing to an emerging public health problem. Third, tobacco industry support for the vaping of nicotine presents new opportunities for the co-administration of cannabis, namely in a liquid form that may be mixed with nicotine. The co-use of substances is associated with significant gaps in knowledge that should be interpreted in the context of (i) societal changes that challenge current prevention strategies, (ii) other commonly co-used drugs, (iii) and methodological challenges that involve research on statistically rare and societally disapproved behaviours that may attract community disapproval. Innovations in illicit drug development (e.g. new forms of synthetic cannabis), communication, transportation and patterns of use are having an impact on drug markets. New drugs are being developed at an extraordinary rate, often with little known about their effects [3]. Using the internet and social media to communication about drugs means that previously unusual combinations of drugs are supported [4]. The use of the ‘dark web’ to sell drugs increases availability of a wider range of drugs [5]. Newer technologies for the administration of drugs (e.g. vaping) make possible new combinations of co-use. Together these advances direct attention to the emerging problem of a more drug informed population able to access a wider range of drugs and drug use options. Although population studies are consistent in suggesting that polydrug use (effectively consecutive use of various drugs) is common, the population data on concurrent use (co-use) is limited or absent. This is not to deny that data on some patterns of co-use are available, but many combinations are poorly documented (e.g. alcohol and amphetamines [6], alcohol and cannabis [7], heroin and cocaine [8]). Although a specific pattern of co-use may be rare, the simultaneous use of various combinations of drugs is not uncommon [9] and warrants attention as an emerging public health concern. The methodological demands associated with the study of statistically rare and surreptitious behaviours are substantial. The suggestion that this be addressed in studies of patient (affected) population's places severe limitations on the generalisability of findings [2]. At a population level there is a need to know what combinations are being used and the frequency and quantity of use as well as the proportions of those using particular combinations of drugs that experience adverse outcomes. Some of these adverse outcomes (e.g. severe mental illnesses) may be predicted by the social and environmental background of the affected person, a possibility that cannot be effectively addressed in a patient only sample. Further, there is a need to know whether some adverse life experiences or outcomes may precede and lead to the use of particular drug co-use, again, not able to be addressed in a selected patient sample. Representative population based research is difficult when large samples are needed, and the behaviours of interest are rare. Some possible solutions present themselves. In some countries there are records of whole populations. These records would need to be linked to behavioural data on patterns of use but could provide population estimates of rare behaviours and their consequences. A second possibility would be to screen large samples for patterns of drug use and only follow-up those with a particular pattern of use and a comparison, non-using group. Neither of these solutions is simple or without challenges, however, the changing nature of drug use and the health concerns such use raises demands a more creative response from the research community. Hindocha and McClure [2] have alerted us to one pattern of co-use that demands attention and also to the changing nature of drug markets and the changing practices of drug users. None.