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Matters of Substance

Cannabis policy challenges

Wednesday, October 31, 2007

In an ideal world, public policies towards cannabis would be informed by both evidence on the personal harms it causes and social and economic evaluations of the costs and benefits of alternative policies in minimising these harms. A paucity of both types of evidence is a major challenge to the development of such “evidence-based” policies towards cannabis use.


There is a limited quantity and quality of research into the health effects of cannabis, but it is nonetheless possible to identify its most probable adverse health effects. These include: an increased risk of motor vehicle crashes if users drive while intoxicated; the development of dependence; increased respiratory symptoms; poorer mental health, including increased risks of psychosis and possibility of depression; and poorer adolescent development, including early school leaving and increased risk of using other illicit drugs.

There is less research into costs and benefits of cannabis policies because, internationally, a narrow range of policy approaches is available for evaluation. These generally involve marginal differences in penalties for cannabis use and possession (for example, imposing fines or counselling rather than imprisonment). The effects of these changes in penalties are likely to be small, and none has been detected in evaluations to date. Evaluations of the more controversial Netherlands cannabis policy – decriminalising personal cannabis use and small-scale retail sales in coffee shops – have come to different conclusions about its effects on rates of use.

Public debate about cannabis policy has often been radically simplified by the media. The public has been invited to believe either that cannabis use is harmless, and hence should be decriminalised (if not legalised), or that cannabis is harmful to health, and so its use should continue to be prohibited. As a consequence, public debate often presents highly polarised evaluations of the health effects of cannabis, with any rational discussion of its health risks the first casualty.

Proponents of prohibition have taken evidence of harms found among cannabis users at face value, ignoring any alternative explanations. Proponents of reform of the existing laws, by contrast, have discounted evidence of harm caused by cannabis use, while emphasising the social costs of enforcing cannabis prohibition.

Discussions of public policy towards cannabis should use consistent standards in appraising evidence of harm from cannabis use and cannabis policies. Good public policy on cannabis requires investments in epidemiological research on the long-term health consequences of its use and social science research on the costs and benefits of current and alternative policy options.

The epidemiological research need not be expensive if cannabis use is routinely asked about in prospective studies of adolescent development, as has been done in New Zealand or in longitudinal studies of adult health such as those in the USA. Another critical ingredient for policy progress is a wider public involvement in the debate. A more realistic understanding of the health effects of cannabis and the impact of cannabis policies requires less partisan appraisals than usually dominate media debates.

Better evidence on the harms of use and cannabis policies is important, but it cannot determine what cannabis policy we should have. In pluralistic social democracies like New Zealand and Australia, social policies in controversial areas like cannabis use must involve a search for a societal compromise that is the most acceptable to the most people (or least objectionable to the fewest). This is because cannabis policy must balance competing social values that are in conflict, namely, the individual freedom of adults to use cannabis, protecting the health of young people, reducing crime, minimising the societal costs of enforcing widely broken laws, and so on.

There is no consensus on what priority these competing social values should be given, so policy debates in democratic societies are and ought to be resolved by a deliberative political process. The political process should take into account evidence on both the harms caused by cannabis use and those that arise from the social policies we implement to prevent its use and resulting harm. This holds the greatest prospect of producing a cannabis policy that enjoys broad community support and best reduces related harm.