Does liberalizing cannabis laws increase cannabis use?

Dr Peter Gates

Interest in research on the impact of liberalising or legalising cannabis use is mounting. Following almost a century of global prohibition on cannabis use and production (chiefly following the 1925 Geneva Convention on Opium and Other Drugs), we are now in what appears to be a changing political climate. In fact, cannabis use and production was recently legalised in Washington and Colorado in the United States, as well as in Uruguay in South America. Interestingly, the consequences of this change to legal cannabis are not yet understood but are fervently debated. Individuals who support legalisation cite probable savings related to reducing criminalisation expenses and that, given the prevalence of illicit use, rates of use are unlikely to increase dramatically. Individuals who oppose legalisation cite concerns that individuals will begin using cannabis at earlier ages (and be at greater risk of harm), that overall prevalence may increase, and that commercial production may lead to the next “Big Tobacco”. Other important changes from complete prohibition have taken place and some jurisdictions in Europe, the UK and Australia have decriminalised cannabis use. Unfortunately, research on the impact of decriminalisation is also scarce, however; Australia is in a significant position in that it has collected national prevalence information on cannabis use before and after this change to policy.

Williams and Bretteville-Jensen (2014) provide a concise history of cannabis policy in Australia. Decriminalisation of cannabis use was first introduced in South Australia in 1987, which meant that being caught with small quantities of cannabis for personal use an offence punishable by payment of a fine without criminal conviction. Other states and territories followed suit after much political debate and cannabis was decriminalised in the Australian Capital Territory in 1992, the Northern Territory in 1995, and Western Australia in 2004. In the other states of Australia any cannabis offence is considered a criminal offence, however; it is unlikely that first time offenders would receive conviction as, depending on the discretion of the police involved, most individuals would instead be diverted to receive mandatory education and treatment.

Using data from the 1998 – 2010 Australian National Drug Strategy Household Survey, Williams and Bretteville-Jensen (2014) were able to use the retrospective recall of participants aged 20-40 years to determine the average ages of initiation to cannabis use across the calendar time period of 1970 – 2010. Participants were aged 30.9 years on average and 41% were male. Interestingly, lifetime use of cannabis was more prevalent in those states and territories where cannabis was decriminalised (63% compared to 55%), as was lifetime use by age 18 (47% compared to 37% reported use before turning 19) and by age 40 (64% compared to 55% reported use before turning 41). To try to better understand the impact of decriminalisation the authors were able to use statistical methods to account for the fixed effects of the time the policy was introduced in separate states and territories and different aspects of possible measurement error. As a result of their sophisticated analysis, the authors found that, following the first five years from policy change, minors who lived under decriminalisation regimes were 12% more likely to initiate cannabis use compared to an otherwise similar minor in states were cannabis use is a criminal offence. Also, the peak age of uptake shifted from 18 years to 16 years in states that decriminalised cannabis. Notably there was no significant difference in the uptake of cannabis by age 40 years between the two policy regimes, indicating that decriminalisation does not affect whether an individual ever uses cannabis.

Although these effects of introducing decriminalisation were significant only during the first handful of years following the policy change, it is important to consider the impact of any change that reduces the age at which individuals begin to use cannabis. This is because there is a significant body of literature that shows an association between early initiation and increased likelihood of developing mental health concerns such as psychosis, developing behavioural issues, and leaving school early.

 

Reference:

Williams, J. & Bretteville-Jensen, A.L. (2014). Does liberalizing cannabis laws increase cannabis use? Journal of health economics 36, 20-32.