1 Introduction

In most, perhaps all, areas of public policy, interventions designed to achieve one goal have effects on other goals as well; some of these unintended consequences are undesirable, others are desirable. For example, an effort to improve social protections for workers by raising mandatory retirement contributions may lead to less formal sector employment and more workers moving to the less protected informal sector jobs (a negative consequence). Or raising the minimum schooling age in order to improve productivity may lead to less crime because a high risk group of youth spends more time in school rather than on the streets (a positive consequence). Systematic evaluation of public policy, for example through cost benefit analysis, routinely takes such effects into account by requiring a listing of all the consequences of the intervention being evaluated, not just of the intended effects (e.g. Gramlich, 1990). The European Commission now requires any ex-ante impact assessments for major policy initiatives identify the potential unintended effects as well as the intended effects.

What is distinctive about policies aimed at illicit drugs is that to many observers, particularly those critical of prohibition or of highly punitive implementation of prohibition, the negative unintended consequences appear more substantial than the intended main effects (e.g. Nadelmann, 1989). For example some claim that tough enforcement of criminal laws against the possession of marijuana, intended to reduce the number of people who use marijuana, has little consequence for the prevalence of marijuana use1 but large consequences in reducing the employment prospects of the arbitrarily selected set of marijuana users who end up convicted of a criminal offense.2 Similarly it is asserted that the spraying of coca fields in Colombia does little if anything to lower the availability or raise the price of cocaine in the United States but causes considerable environmental damage in the areas subject to spraying. There may be unintended positive consequences; these rarely get mentioned.

There is an asymmetry here. The intended consequences, lower rates of use and harm, are almost by definition difficult to observe; they are events that did not occur. To estimate them requires the specification and measurement of a counter-factual, namely what use or harm would have been, absent the interventions. On the other hand the unintended consequences are conspicuous and readily traced to their source.

In the debate about prohibition, these unintended consequences of enforcement policies play a major role, particularly for civil society.3 Even for the leading international drug control official, the Executive Director of the UN Office of Drugs and Crime, the unintended consequences are highly significant. In a recent much cited paper, the Executive Director identifies five broad classes of unintended consequences that should play a role in discussions of policy: creation of huge criminal black markets, policy displacement (from health to enforcement against those markets), geographic displacement, substance displacement (to less controllable drugs) and change in the way we perceive and deal with the users of illicit drugs (Costa, 2008).

The purpose of this report is to provide a systematic discussion of unintended consequences of policies aimed at reducing drug use and related problems, focused on the mechanisms that generate these consequences. There is no claim to completeness or quantitative precision, simply because the topic is not well explored, being employed primarily for debating or rhetorical purposes to date.

Chapter 1 deals with terminological issues. The following chapter presents a taxonomy of mechanisms generating the unintended consequences, which should help in integrating them into analysis of drug policy interventions. Chapter 3 relates this taxonomy to the concepts presented by Costa. Chapter 4 briefly discusses positive unintended consequences while Chapter 5
then considers the implications of the analysis for policy purposes.

1 For a review of the effects of enforcement on marijuana use, see Room et al., 2008.
2 This was an important element of the argument for removing criminal penalties for simple possession of marijuana in Western Australia in 2002. See, for example, Lenton et al., 2000.
3 An odd feature of the drug policy debate is that the unintended consequences are mostly raised by liberal critics of state policies. Hirschman (1991), in a widely cited book, argued