Findings from the DUMA program: The influence of cannabis dependency and use on criminal offending, through the eyes of police detainees.

Dr Susan Goldsmid


Cannabis is the most widely used illicit drug in Australia. One in ten Australians report using cannabis, with prevalence rates highest among males and Indigenous Australians (AIHW, 2011). A recent meta-analysis conducted by Bennett, Holloway and Farrington (2008) reported that a positive relationship exists between cannabis use and offending. Based on a synthesis of results from 10 studies, Bennett and colleagues reported that the odds of cannabis users offending were 1.5 times higher (in terms of an increased odds ratio) than the odds of non-cannabis users offending. When the prevalence of cannabis use in the general population is considered, even a small rise in odds of offending for cannabis users could translate into a notable contribution to crime rates.

The mechanism through which cannabis use may be associated with criminal offending is a complex issue. Theories aimed at explaining such relationships generally fall into one of the following categories: 1) causal (i.e., illicit drug consumption leads to criminal offending, or vice versa); 2) indirect causation (i.e., another variable or set of variables cause both illicit drug consumption and criminal offending); and 3) non-casual (i.e., the association is a result of general associations between delinquency, antisocial behaviour or other such factors) (Bennett, et al. 2008). In 2012, Payne and Gaffney examined perceptions of the role of cannabis use on offending in a sample of Australian police detainees (N= 1,884). Thirteen percent of detainees (n= 120) nominated cannabis use as contributing to their current criminal offending. The most common reasons reported were being high at the time of the offence (36%) or hanging out for cannabis (i.e., experiencing withdrawal symptoms) at the time of the offence (15%). If this relationship is a causal relationship, then it would be expected that at higher levels of cannabis use cannabis would be more likely to contribute to criminal offending, than at lower levels of use. If the underlying relationship is through indirect causation this pattern of association may still be present, if the variable(s) that influence cannabis use and offending do so at a commensurate rate. However, it would not be anticipated that offenders would identify cannabis use as a contributing factor to their criminal offending behaviour. If the underlying relationship is non-causal then an association between higher cannabis use and detainee attributions of cannabis as a causal factor in offending would be unlikely, as under this theory cannabis has no direct association with offending.

The Australian Institute of Criminology s (AIC) Drug Use Monitoring in Australia (DUMA) program is the longest running monitoring program of drug use and crime trends in the Australia police detainee population. On a quarterly basis, detainees held at selected watch-houses across Australia are invited to participate in the DUMA program. This involves completion of an interviewer-assisted self-report questionnaire aimed at gathering information about the detainee s drug use, patterns of offending and related issues. Detainee participation in the DUMA program is voluntary and anonymous. In 2013, DUMA data was collected at East Perth, Brisbane, Adelaide, Kings Cross and Surry Hills police stations.

Demographic information, cannabis use and cannabis dependency were assessed through a series of self-report questionnaire items. Detainees who reported cannabis use in the 30 days prior to detention were asked to indicate the extent to which they thought cannabis use contributed to their current criminal offending. Response options were Not at all , A little , A lot and Don t know . The response options of A little and A lot were combined to provide an affirmative response to cannabis as a contributing factor to offending.

Cannabis use among Australian detainees
Of the 1,149 detainees interviewed as part of the DUMA program in 2013, 50.3 percent (n=578) self-reported cannabis use in the previous 30 days and 31.0 percent (n=356) of detainees reported use in the 48 hours prior to detention by police. Cannabis was on average consumed on 13.4 (SD=12.5) days out of the previous 30 days, with 12.4 percent of cannabis using detainees (n=142) reporting daily use. Cannabis was on average consumed 3.2 (SD= 3.7) times per day.
Of the 685 detainees who reported cannabis use in the previous 12 months, 37.1 percent (n=254) reported that they felt that they were dependent on cannabis. Of concern, 94.9 percent (n=241) of detainees who reported dependence also reported cannabis use in the previous 30 days, suggesting an unmet need for treatment.

Attribution of cannabis use to offending
Of the detainees who reported cannabis use in the 30 days prior to detention (n=571), 17.5 percent (n=100) stated that they thought that cannabis contributed a little or a lot to what happened to prompt their current detention by police.
When asked to describe the role that cannabis played in what happened, 30 detainees reported that they were high on cannabis at the time, 12 detainees reported that they needed money to buy cannabis, 9 detainees that they were hanging out for cannabis and 55 detainees cited other reasons . Detainees could provide multiple responses. Of those detainees that cited other reasons (n= 55), the reasons included being detained for cannabis related charges such as possession or supply (n=36), mental health related issues connected to cannabis use (n=6) and behaviour or cognitive changes attributed to intoxication (n=7).
Self-reported dependence on cannabis was significantly related to identifying cannabis use as contributing to current criminal offending, X2(1) = 39.5, p<.05. Twenty-six percent of dependent versus eight percent of non-dependent cannabis users identified cannabis as contributing to current offending.

Detainees who attributed their criminal offending to cannabis use (M=22.2, SD=1.1) reported a higher number of days of use in the previous 30 days than did cannabis using detainees who did not attribute offending to cannabis use (M=14.6, SD=0.6), t(569)=-5.9, p<.05. Cannabis users who reported that cannabis contributed to current offending (M=3.9, SD=0.4) also reported higher frequency of cannabis use per day than detainees who did not report cannabis use as a contributing factor (M=3.0, SD=0.2), t(556)=-2.2, p<.05.

Detainees with cannabis dependency and those who use cannabis at higher frequencies were more likely to identify cannabis use as contributing to their current criminal offending. Detainees most commonly reported that it was the psychological and behavioural impact of intoxication or withdrawal from cannabis that contributed to offending. Detainee perceptions suggest a direct causal link, through intoxication effects. Only 20.5% of detainees who reported cannabis use in the 48 hours prior to detention reported cannabis as a contributing factor. Thus, the contribution of cannabis to offending may have been under-estimated by detainees. Alternatively, it may be that it is frequency of cannabis use and not proximity of consumption to offending that determines the contributing role that cannabis use plays in engagement in criminal behaviour.
Indigenous detainees reported a significantly higher number of days of cannabis use and slightly higher frequency of use per day, in the previous 30 days, than non-Indigenous detainees. This is consistent with higher prevalence rates of cannabis use among Indigenous persons reported within general community samples (AIHW, 2011). There was no difference between Indigenous and non-Indigenous detainees in terms of self-reported cannabis dependency. This issue would benefit from further research as it would be anticipated that higher usage rates would be associated with higher self-reported dependency. The apparent disparity in the findings may reflect less ability or less willingness among Indigenous persons to self-identify cannabis dependency. If this is the case, it may be adversely impacting upon help-seeking behaviours within this population.
Detainee reports of cannabis use and its role in criminal offending may have been adversely influenced by a number of factors. Detainees may have over-inflated the role that cannabis use played in offending in order to mitigate responsibility for their criminal behaviour. Under-reporting may have also occurred due to stigma associated with illicit drug use and with offending, or in an attempt to avoid implicating themselves in further offences. The anonymous and confidential nature of the survey was structured to minimise the influence of these factors on reporting. A further limitation of the study is that heavily intoxicated offenders are excluded from participating.
There were no gender differences in cannabis dependency and frequency of cannabis use in this study. This is contrary to gender differences observed in general community samples (AIHW, 2011). The findings need to be interpreted with caution due to the over representation of males within the sample. There is a much higher ratio of males to females in the police detainee population from which this sample was derived.

There appears to be a high degree of unmet need for treatment for cannabis dependency among Australian detainees. Almost all detainees who self-reported cannabis dependency also reported recent cannabis use. The adverse impact of cannabis dependency on the mental and physical health of users is well documented. The current study illustrates the added social cost of this unmet need for treatment in terms of criminal offending. Detainees who reported that cannabis use contributed to their offending were more likely to be dependent on cannabis and to use cannabis at a higher frequency, than detainees who reported no such contribution to their offending.

Australian Institute of Health and Welfare. (2011). 2010 National Drug Strategy Household Survey report. Drug statistics series no. 25. Cat. no. PHE 145. Canberra: AIHW.
Bennett, T., Holloway, K., & Farrington, D. (2008). The statistical association between drug misuse and crime: A meta-analysis. Aggression and Violent Behavior,13, 107-118.
Payne, J. & Gaffney, A. 2012. How much crime is drug or alcohol related? Self-reported attributions of police detainees. Trends & Issues in Crime and Criminal Justice no. 439. Canberra: The Australian Institute of Criminology.