Cannabis is the cutting-edge drug for reform, the only politically plausible candidate for major legal change, at least decriminalisation (removal of criminal penalties for possession) and perhaps even outright legalisation (permitting production and sale). Compared with other drugs, the harms, physiological or behavioural, are less severe and the drug is better integrated into the culture. Throughout Western Europe and in the Antipodes there is pressure for reductions in the punitiveness of the marijuana regime.

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This paper attempts to project the likely consequences of substantial changes in the basic legal regime for cannabis and to offer an assessment of those consequences. The best evidence on the effects of liberalising marijuana policy comes from The Netherlands which has experienced both decriminalisation and commercialisation, though without ever changing formal law. In this paper, we summarise and extend our analysis of the Dutch cannabis policy (MacCoun & Reuter, 1997).

The Dutch experience, together with those of a few other countries with more modest policy changes, provides a moderately good empirical case that removal of criminal prohibitions on cannabis possession (decriminalisation) will not increase the prevalence of marijuana or any other illicit drug; the argument for decriminalisation is thus strong. Making cannabis fully legal is likely to increase its use substantially because of promotion, particularly in the USA with its peculiar dedication to commercial free speech; that is possibly undesirable. An intermediate model can be devised which may be preferable to either legalisation or simple decriminalisation.

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Results: The available evidence indicates that depenalisation of the possession of small quantities of cannabis does not increase cannabis prevalence. The Dutch experience suggests that commercial promotion and sales may significantly increase cannabis prevalence.

Conclusions: Alternatives to an aggressively enforced cannabis prohibition are feasible and merit serious consideration. A model of depenalised possession and personal cultivation has many of the advantages of outright legalisation with few of its risks.

The basis for continued cannabis prohibition

The case for continued prohibition of nonmedical uses of marijuana rests primarily on four possible harms: (a) marijuana's role as a gateway to other drugs of known dangerousness, a role generally believed to be unrelated to its legal status; (b ) the health consequences and impact on adolescent development; (c ) behaviour when intoxicated; and (d) the difficulty of quiting. We think none of these turns out to be very substantial; in particular, the gateway effect (which has seven possible interpretations) has probably been greatly overstated.

Our judgement, based on review of the research literature, is that at present the primary harms of marijuana use (including those borne by non-users) come from criminalisation: expensive and intrusive enforcement, inequity, shock to the conscience from disproportionate sentence and a substantial (though generally non-violent) black market. Certainly the drug itself causes damage: it generates accidents causing harm to both the user and others; regular use by adolescents may adversely affect development; it may have some substantial impact on the prevalence of cancer among frequent users; a non-trivial share of users has difficulty quitting when they wish to and see their lives as somewhat harmed because of their dependence. But the adverse consequences of criminalisation, at least with current US enforcement, seem more substantial.

The available evidence suggests that removal of the prohibition against possession itself (decriminalisation) does not increase cannabis use. In addition to the Dutch experience from 1976 to 1983, we have similar findings from analysis of weaker decriminalisations (with fines retained for the offence of simple possession of small quantities) in 12 US states (Single, 1989) and South Australia and the Australian Capital Territory (Hall, 1997; McGeorge & Aitken, 1997). The fact that Italy and Spain, which have decriminalised possession for all psychoactive drugs, have marijuana use rates comparable to those of neighbouring countries provides further support. This prohibition inflicts harms directly and is costly. Unless it can be shown that the removal of criminal penalties will increase use of other more harmful drugs, perhaps because of the signal of lessened disapproval, it is difficult to see what society gains.

Decriminalisation is normatively flawed (why does sale remain illegal?) and still leaves the harms of black markets. However, the removal of the sales prohibition has more complex effects. We believe that it would generate larger increases in marijuana use as a result of promotion by the legal suppliers. Promotion could not be effectively limited in the US commercial marketplace for a product which, with no therapeutic goal, would be provided in conventional commerce rather than through doctors and pharmacies. Recent experience with legalised gambling, as well as the difficulty of suppressing cigarette promotion, added to the post-World War II erosion of repeal's liquor controls, all suggest that legal commercial interests are likely to weaken regulatory efforts. This is especially plausible for marijuana, whose harms are relatively slight, hence complicating the task of defending stringent regulation against the efforts of a legal industry. If, even with relatively tight regulation, The Netherlands saw a large increase in marijuana prevalence, US legalisation might lead to very high prevalence rates indeed. The increase in marijuana use would have to be weighed against the reduced intrusiveness of the state, reduction of black markets and possible substitution of marijuana for alcohol, which might be net health enhancing.

Other regimes between decriminalisation and commercialisation are possible. For example, the state of Alaska permits home production for own consumption and gifts to others. The impact on prevalence is difficult to determine (Segal, 1990) but it may be an appropriate compromise between the excess of commercialisation and the barren rights of decriminalisation. Our purpose here is not to choose an optimal regime but only to suggest that available evidence provides a basis for a reasonable debate about the likely consequences of regime changes.