Cannabis supply and consumption of other drugs

Dr Susan Goldsmid

Introduction

In 2012-13, Australian cannabis seizures, in terms of number and weight, were the highest recorded in the last decade, with 21.5 kilograms of cannabis detected at the border, the majority of which was cannabis seeds (ACC, 2014). Evidence suggests supply-side drug law enforcement can positively contribute to harm reduction (Weatherburn, Jones, Freeman & Makkai, 2003). However, such benefits can be mitigated by unintended adverse outcomes, such as increased consumption of other illicit drugs (Weatherburn, et al. 2003). The aim of this report is to examine the effect that reductions in cannabis availability has on cannabis, alcohol and other illicit drug consumption.

In 2001, the responses of cannabis users to hypothetical scenarios of reduced cannabis supply or a doubling in the price of cannabis were examined in a sample of New South Wales (NSW) residents between 18 and 29 years of age (N = 223) who reported use of cannabis in the previous 12 months (Jones & Weatherburn, 2001). If confronted by a reduction in supply, 48.5% of users stated that they would either reduce (22.9%) or stop (25.6%) their consumption of cannabis. If the price of cannabis was to double, 26.9% and 31.8% of users stated they would reduce or stop their use of cannabis, respectively. However, 31.6% of users stated that under these scenarios they would drink more alcohol and 8.4% of users stated that they would switch to using other illicit drugs. This suggests there would be a minimal, if any, net gain in terms of harm minimisation. A limitation of these findings is that they represent cannabis users’ intentions which may or may not correspond to actual behaviour during periods of reduced cannabis supply.

Using data from the Australian Institute of Criminology’s Drug Use Monitoring in Australia (DUMA) program, an examination is presented of retrospective self-reports from cannabis users of the impact that periods of reduced cannabis supply had on their consumption of cannabis, alcohol and other illicit drugs.

Since 1999, the Australian Institute of Criminology (AIC) has monitored drug use and crime trends across Australia through DUMA. Each quarter, detainees held in watch-houses at various sites across Australia are asked to complete an interviewer-assisted self-report questionnaire and provide a urine sample. This data allows monitoring of the availability of illicit substances, including cannabis, and examinations of crime and drug usage behaviours. In quarter 3 of 2013, detainees who had indicated cannabis use in the previous 12 months, were presented with additional questions to assess whether the detainee had previously experienced a period when cannabis was hard to get and if they had, how this had affected their use of cannabis, alcohol and other illicit drugs.

Cannabis consumption during periods of reduced cannabis supply

Of the 549 detainees interviewed in the third quarter of 2013 DUMA data collection (conducted at East Perth, Brisbane, Adelaide and Kings Cross watch-houses), 60.3% reported using cannabis in the previous 12 months. The majority of detainees were male (80.7%); the over representation of males in the sample is consistent with the male to female ratio in the detainee population. Detainees had an average age of 32 years.

Cannabis is the illicit substance most commonly used by Australian detainees. In quarter 3 of 2013, of the 375 detainees who voluntarily supplied a urine sample, 51.5% tested positive for cannabis. This rate is considerably higher than that recorded for amphetamines (36.0%; 135 of 375) and opiates (21.3%; 80 of 375). There was a high rate of poly-drug use among detainees, with 26.0% of samples testing positive to two or more drugs. In 75.5% of poly-drug use cases, cannabis was one of the drugs used.

Detainee reports on the current state of the cannabis market indicated that across Australia there had been little movement in cannabis availability in the three months prior to interview. Of those detainees who reported market changes, the number that reported an increase was almost equal to those who reported a decrease in availability (Table 1). Based on a scale of 1 (extremely hard to get) to 10 (readily available), detainees across Australia consistently reported ease in accessing cannabis. On average, Brisbane detainees reported ease at 8.1; East Perth detainees, 7.9; Kings Cross detainees, 7.4; and Adelaide detainees, 7.2.

Fluctuations in the price of cannabis can be in response to a number of different changes in market conditions, including a change in level of supply or a change in demand. When asked about recent changes in the price of cannabis, 27.2% of detainees reported the price of cannabis had become more expensive; 57.0% reported it had stayed the same; 2.5% reported it had become less expensive; 4.2% the price fluctuated; and 9.2% reported that they didn’t know.

Detainees were then asked to consider the last time cannabis was hard to get and the impact the reduction in supply had on their use of cannabis (Table 2). Of those detainees who reported experiencing a period of reduced cannabis availability (N = 140), the majority reported in times of reduced supply they consumed less cannabis either by reducing the quantity they consumed (32.1%) or by abstaining (47.9%). There was a consistent pattern of reduced consumption across all geographical regions.

Alcohol and other illicit drug (non-cannabis) consumption during periods of reduced cannabis supply

The reported impact of a reduction in the supply of cannabis on detainee’s use of alcohol and illicit drugs other than cannabis is presented in Table 3. Only a minority of detainees self-reported an increased consumption of alcohol (20.9%; 28 of 134 detainees) or other illicit drugs (12.7%; 17 of 135) during periods of reduced cannabis supply. Given a sizable percentage of detainees (26.0%) are poly drug users (users of two or more substances), the data can be interpreted as suggesting that during periods of reduced cannabis supply the majority of detainees continued to use alcohol and other illicit drugs at rates commensurate with periods in which cannabis is readily available, rather than a switch to using new substances.

Conclusion

In terms of harm minimisation, supply-reduction approaches to cannabis appear to have merit. The majority of cannabis-using detainees reported when periods of reduced cannabis supply have been experienced they either reduced consumption or abstained from cannabis. For the majority this occurred without an increase in the consumption of alcohol or other illicit drugs.

A limitation of this study is it relies on retrospective self-reports of drug use. Retrospective reports of behaviour are considered to be a valid method of assessment, but in the detainee population low education levels and the impact of drug use on cognitive function may undermine the reliability of this measurement technique. To overcome this, future studies may consider examining trends in detainee use of alcohol and illicit substances, measured via self-reports and urinalysis, in periods where contemporaneous detainee reports indicate reduced cannabis supply. Caution should be taken in generalising these findings to non-detainee cannabis-using populations, as they are likely to substantially differ in terms of socioeconomic status and exposure to the drug market.

If replicated, the current findings have two clear implications. First, the findings suggest policy and policing efforts aimed at reducing cannabis supply may result in reductions in harm among cannabis users. Second, periods of reduced cannabis supply may present valuable opportunities for the implementation of demand reduction measures, such as treatment or education initiatives. The efficacy of such initiatives may be enhanced during periods of reduced supply, due to users self-initiating abstinence or reduced cannabis consumption.

References

Australian Crime Commission 2014. 2012-13 Illicit Drug Data Report. Canberra: ACC

Jones C & Weatherburn D. 2001. Reducing Cannabis Consumption. Crime and Justice Bulletin no. 60. Sydney: NSW Bureau of Crime Statistics and Research.

Weatherburn, D., Jones, C., Freeman, K. & Makkai, T. 2003. Supply control and harm reduction: lessons from the Australian heroin ‘drought’. Addiction, 98, 83-91.